Version: 261.2.4

83ad6042a7 & b267cd6fb4

Does not include test code to avoid risking merge conflicts.

(cherry picked from commit 415585a30d74fcae61f581808220a7aaeca3eaf5)
(cherry picked from commit e36628a6d436ea08d6d31441c101a88a5504c515)

MSBuild/Robust.Engine.Version.props

@@ -1,4 +1,4 @@
 <Project>
 
-    <!-- This file automatically reset by Tools/version.py -->
+    <!-- This file automatically reset by Tools/version.py -->
 

MSBuild/XamlIL.targets

@@ -71,6 +71,6 @@
     </PropertyGroup>
     <Exec
       Condition="'$(_RobustUseExternalMSBuild)' == 'true'"
-      Command="&quot;$(DOTNET_HOST_PATH)&quot; msbuild /nodereuse:false $(MSBuildProjectFile) /t:CompileRobustXaml /p:_RobustForceInternalMSBuild=true /p:Configuration=$(Configuration) /p:RuntimeIdentifier=$(RuntimeIdentifier) /p:TargetFramework=$(TargetFramework) /p:BuildProjectReferences=false"/>
+      Command="&quot;$(DOTNET_HOST_PATH)&quot; msbuild /nodereuse:false $(MSBuildProjectFile) /t:CompileRobustXaml /p:_RobustForceInternalMSBuild=true /p:Configuration=$(Configuration) /p:RuntimeIdentifier=$(RuntimeIdentifier) /p:TargetFramework=$(TargetFramework) /p:BuildProjectReferences=false /p:IntermediateOutputPath=&quot;$(IntermediateOutputPath.TrimEnd('\'))/&quot;"/>
   </Target>
 </Project>

RELEASE-NOTES.md

@@ -54,13 +54,252 @@ END TEMPLATE-->
 *None yet*
 
 
-## 255.0.3
+## 261.2.4
 
 
-## 255.0.2
+## 261.2.3
 
 
-## 255.0.1
+## 261.2.2
+
+
+## 261.2.1
+
+
+## 261.2.0
+
+### New features
+
+* Implement IEquatable for ResolvedPathSpecifier & ResolvedCollectionSpecifier.
+* Add NearestChunkEnumerator.
+
+### Bugfixes
+
+* Fix static entities not having the center of mass updated.
+* Fix TryQueueDelete.
+* Fix tpto potentially parenting grids to non-map entities.
+
+### Other
+
+* TileChangedEvent is now raised once in clientside grid state handling rather than per tile.
+* Removed ITileDefinition.ID as it was redundant.
+* Change the lifestage checks on predicted entity deletion to check for terminating.
+
+### Internal
+
+* Update some `GetComponentName<T>` uses to generic.
+
+
+## 261.1.0
+
+### New features
+
+* Automatically create logger sawmills for `UIController`s similar to `EntitySystem`s.
+
+### Bugfixes
+
+* Fix physics forces not auto-clearing / respecting the cvar.
+
+### Internal
+
+* Cleanup more compiler warnings in unit tests.
+
+
+## 261.0.0
+
+### Breaking changes
+
+* Remove unused TryGetContainingContainer override.
+* Stop recursive FrameUpdates for controls that are not visible.
+* Initialize LocMgr earlier in the callstack for GameController.
+* Fix FastNoiseLise fractal bounding and remove its DataField property as it should be derived on other properties updating.
+* Make RaiseMoveEvent internal.
+* MovedGridsComponent and PhysicsMapComponent are now purged and properties on `SharedPhysicsSystem`. Additionally the TransformComponent for Awake entities is stored alongside the PhysicsComponent for them.
+* TransformComponent is now stored on physics contacts.
+* Gravity2DComponent and Gravity2DController were moved to SharedPhysicsSystem.
+
+### New features
+
+* `IFileDialogManager` now allows specifying `FileAccess` and `FileShare` modes.
+* Add Intersects and Enlarged to Box2i in line with Box2.
+* Make `KeyFrame`s on `AnimationTrackProperty` public settable.
+* Add the spawned entities to a returned array from `SpawnEntitiesAttachedTo`.
+
+### Bugfixes
+
+* Fixed SDL3 file dialog implementation having a memory leak and not opening files read-write.
+* Fix GetMapLinearVelocity.
+
+### Other
+
+* `uploadfile` and `loadprototype` commands now only open files with read access.
+* Optimize `ToMapCoordinates`.
+
+### Internal
+
+* Cleanup on internals of `IFileDialogManager`, removing duplicate code.
+* Fix Contacts not correctly being marked as `Touching` while contact is ongoing.
+
+
+## 260.2.0
+
+### New features
+
+* Add `StringBuilder.Insert(int, string)` to sandbox.
+* Add the WorldNormal to the StartCollideEvent.
+
+
+## 260.1.0
+
+### New features
+
+* `ComponentFactory` is now exposed to `EntitySystem` as `Factory`
+
+### Other
+
+* Cleanup warnings in PLacementManager
+* Cleanup warnings in Clide.Sprite
+
+## 260.0.0
+
+### Breaking changes
+
+* Fix / change `StartCollideEvent.WorldPoint` to return all points for the collision which may be up to 2 instead of 1.
+
+### New features
+
+* Add SpriteSystem dependency to VisualizerSystem.
+* Add Vertical property to progress bars
+* Add some `EntProtoId` overloads for group entity spawn methods.
+
+
+## 259.0.0
+
+### Breaking changes
+
+* TileChangedEvent now has an array of tile changed entries rather than raising an individual event for every single tile changed.
+
+### Other
+
+* `Entity<T>` methods were marked as `readonly` as appropriate.
+
+
+## 258.0.1
+
+### Bugfixes
+
+* Fix static physics bodies not generating contacts if they spawn onto sleeping bodies.
+
+
+## 258.0.0
+
+### Breaking changes
+
+* `IMarkupTag` and related methods in `MarkupTagManager` have been obsoleted and should be replaced with the new `IMarkupTagHandler` interface. Various engine tags (e.g., `BoldTag`, `ColorTag`, etc) no longer implement the old interface.
+
+### New features
+
+* Add IsValidPath to ResPath and make some minor performance improvements.
+
+### Bugfixes
+
+* OutputPanel and RichTextLabel now remove controls associated with rich text tags when the text is updated.
+* Fix `SpriteComponent.Visible` datafield not being read from yaml.
+* Fix container state handling not forcing inserts.
+
+### Other
+
+* `SpriteSystem.LayerMapReserve()` no longer throws an exception if the specified layer already exists. This makes it behave like the obsoleted `SpriteComponent.LayerMapReserveBlank()`.
+
+
+## 257.0.2
+
+### Bugfixes
+
+* Fix unshaded sprite layers not rendering correctly.
+
+
+## 257.0.1
+
+### Bugfixes
+
+* Fix sprite layer bounding box calculations. This was causing various sprite rendering & render-tree lookup issues.
+
+
+## 257.0.0
+
+### Breaking changes
+
+* The client will now automatically pause any entities that leave their PVS range.
+* Contacts for terminating entities no longer raise wake events.
+
+### New features
+
+* Added `IPrototypeManager.IsIgnored()` for checking whether a given prototype kind has been marked as ignored via `RegisterIgnore()`.
+* Added `PoolManager` & `TestPair` classes to `Robust.UnitTesting`. These classes make it easier to create & use pooled server/client instance pairs in integration tests.
+* Catch NotYamlSerializable DataFields with an analyzer.
+* Optimized RSI preloading and texture atlas creation.
+
+### Bugfixes
+
+* Fix clients unintentionally un-pausing paused entities that re-enter pvs range
+
+### Other
+
+* The yaml prototype id serialiser now provides better feedback when trying to validate an id for a prototype kind that has been ignored via `IPrototypeManager.RegisterIgnore()`
+* Several SpriteComponent methods have been marked as obsolete, and should be replaced with new methods in SpriteSystem.
+* Rotation events no longer check for grid traversal.
+
+
+## 256.0.0
+
+### Breaking changes
+
+* `ITypeReaderWriter<TType, TNode>` has been removed due to being unused. Implement `ITypeSerializer<TType, TNode>` instead
+* Moved AsNullable extension methods to the Entity struct.
+
+### New features
+
+* Add DevWindow tab to show all loaded textures.
+* Add Vector2i / bitmask converfsion helpers.
+* Allow texture preload to be skipped for some textures.
+* Check audio file signatures instead of extensions.
+* Add CancellationTokenRegistration to sandbox.
+* Add the ability to serialize TimeSpan from text.
+* Add support for rotated / mirrored tiles.
+
+### Bugfixes
+
+* Fix yaml hot reloading.
+* Fix a linear dictionary lookup in PlacementManager.
+
+### Other
+
+* Make ItemList not run deselection callback on all items if they aren't selected.
+* Cleanup warnings for CS0649 & CS0414.
+
+### Internal
+
+* Move PointLight component states to shared.
+
+
+## 255.1.0
+
+### New features
+
+* The client localisation manager now supports hot-reloading ftl files.
+* TransformSystem can now raise `GridUidChangedEvent` and `MapUidChangedEvent` when a entity's grid or map changes. This event is only raised if the `ExtraTransformEvents` metadata flag is enabled.
+
+### Bugfixes
+
+* Fixed a server crash due to a `NullReferenceException` in PVS system when a player's local entity is also one of their view subscriptions.
+* Fix CompileRobustXamlTask for benchmarks.
+* .ftl files will now hot reload.
+* Fix placementmanager sometimes not clearing.
+
+### Other
+
+* Container events are now documented.
 
 
 ## 255.0.0

Resources/Locale/en-US/custom-controls.ftl

@@ -9,6 +9,7 @@ entity-spawn-window-override-menu-tooltip = Override placement
 ## TileSpawnWindow
 
 tile-spawn-window-title = Place Tiles
+tile-spawn-window-mirror-button-text = Mirror Tiles
 
 ## Console
 

Resources/Locale/en-US/dev-window.ftl

@@ -0,0 +1,10 @@
+## "Textures" dev window tab
+
+dev-window-tab-textures-title = Textures
+dev-window-tab-textures-reload = Reload
+dev-window-tab-textures-filter = Filter
+dev-window-tab-textures-summary = Total (est): { $bytes }
+dev-window-tab-textures-info = Width: { $width } Height: { $height }
+    PixelType: { $pixelType } sRGB: { $srgb }
+    Name: { $name }
+    Est. memory usage: { $bytes }

Robust.Analyzers.Tests/DataDefinitionAnalyzerTest.cs

@@ -21,47 +21,53 @@ public sealed class DataDefinitionAnalyzerTest
             },
         };
 
+        test.TestState.Sources.Add(("TestTypeDefs.cs", TestTypeDefs));
+
         // ExpectedDiagnostics cannot be set, so we need to AddRange here...
         test.TestState.ExpectedDiagnostics.AddRange(expected);
 
         return test.RunAsync();
     }
 
+    private const string TestTypeDefs = """
+        using System;
+
+        namespace Robust.Shared.ViewVariables
+        {
+            public sealed class ViewVariablesAttribute : Attribute
+            {
+                public readonly VVAccess Access = VVAccess.ReadOnly;
+
+                public ViewVariablesAttribute() { }
+
+                public ViewVariablesAttribute(VVAccess access)
+                {
+                    Access = access;
+                }
+            }
+            public enum VVAccess : byte
+            {
+                ReadOnly = 0,
+                ReadWrite = 1,
+            }
+        }
+
+        namespace Robust.Shared.Serialization.Manager.Attributes
+        {
+            public class DataFieldBaseAttribute : Attribute;
+            public class DataFieldAttribute : DataFieldBaseAttribute;
+            public sealed class DataDefinitionAttribute : Attribute;
+            public sealed class NotYamlSerializableAttribute : Attribute;
+        }
+    """;
+
     [Test]
-    public async Task Test()
+    public async Task NoVVReadOnlyTest()
     {
         const string code = """
-            using System;
             using Robust.Shared.ViewVariables;
             using Robust.Shared.Serialization.Manager.Attributes;
 
-            namespace Robust.Shared.ViewVariables
-            {
-                public sealed class ViewVariablesAttribute : Attribute
-                {
-                    public readonly VVAccess Access = VVAccess.ReadOnly;
-
-                    public ViewVariablesAttribute() { }
-
-                    public ViewVariablesAttribute(VVAccess access)
-                    {
-                        Access = access;
-                    }
-                }
-                public enum VVAccess : byte
-                {
-                    ReadOnly = 0,
-                    ReadWrite = 1,
-                }
-            }
-
-            namespace Robust.Shared.Serialization.Manager.Attributes
-            {
-                public class DataFieldBaseAttribute : Attribute;
-                public class DataFieldAttribute : DataFieldBaseAttribute;
-                public sealed class DataDefinitionAttribute : Attribute;
-            }
-
             [DataDefinition]
             public sealed partial class Foo
             {
@@ -83,8 +89,8 @@ public sealed class DataDefinitionAnalyzerTest
             """;
 
         await Verifier(code,
-            // /0/Test0.cs(35,17): info RA0028: Data field Bad in data definition Foo has ViewVariables attribute with ReadWrite access, which is redundant
-            VerifyCS.Diagnostic(DataDefinitionAnalyzer.DataFieldNoVVReadWriteRule).WithSpan(35, 17, 35, 50).WithArguments("Bad", "Foo")
+            // /0/Test0.cs(7,17): info RA0028: Data field Bad in data definition Foo has ViewVariables attribute with ReadWrite access, which is redundant
+            VerifyCS.Diagnostic(DataDefinitionAnalyzer.DataFieldNoVVReadWriteRule).WithSpan(7, 17, 7, 50).WithArguments("Bad", "Foo")
         );
     }
 
@@ -92,16 +98,8 @@ public sealed class DataDefinitionAnalyzerTest
     public async Task ReadOnlyFieldTest()
     {
         const string code = """
-            using System;
             using Robust.Shared.Serialization.Manager.Attributes;
 
-            namespace Robust.Shared.Serialization.Manager.Attributes
-            {
-                public class DataFieldBaseAttribute : Attribute;
-                public class DataFieldAttribute : DataFieldBaseAttribute;
-                public sealed class DataDefinitionAttribute : Attribute;
-            }
-
             [DataDefinition]
             public sealed partial class Foo
             {
@@ -114,8 +112,8 @@ public sealed class DataDefinitionAnalyzerTest
             """;
 
         await Verifier(code,
-            // /0/Test0.cs(15,12): error RA0019: Data field Bad in data definition Foo is readonly
-            VerifyCS.Diagnostic(DataDefinitionAnalyzer.DataFieldWritableRule).WithSpan(15, 12, 15, 20).WithArguments("Bad", "Foo")
+            // /0/Test0.cs(7,12): error RA0019: Data field Bad in data definition Foo is readonly
+            VerifyCS.Diagnostic(DataDefinitionAnalyzer.DataFieldWritableRule).WithSpan(7, 12, 7, 20).WithArguments("Bad", "Foo")
         );
     }
 
@@ -123,16 +121,8 @@ public sealed class DataDefinitionAnalyzerTest
     public async Task ReadOnlyPropertyTest()
     {
         const string code = """
-            using System;
             using Robust.Shared.Serialization.Manager.Attributes;
 
-            namespace Robust.Shared.Serialization.Manager.Attributes
-            {
-                public class DataFieldBaseAttribute : Attribute;
-                public class DataFieldAttribute : DataFieldBaseAttribute;
-                public sealed class DataDefinitionAttribute : Attribute;
-            }
-
             [DataDefinition]
             public sealed partial class Foo
             {
@@ -145,8 +135,40 @@ public sealed class DataDefinitionAnalyzerTest
             """;
 
         await Verifier(code,
-            // /0/Test0.cs(15,20): error RA0020: Data field property Bad in data definition Foo does not have a setter
-            VerifyCS.Diagnostic(DataDefinitionAnalyzer.DataFieldPropertyWritableRule).WithSpan(15, 20, 15, 28).WithArguments("Bad", "Foo")
+            // /0/Test0.cs(7,20): error RA0020: Data field property Bad in data definition Foo does not have a setter
+            VerifyCS.Diagnostic(DataDefinitionAnalyzer.DataFieldPropertyWritableRule).WithSpan(7, 20, 7, 28).WithArguments("Bad", "Foo")
+        );
+    }
+
+    [Test]
+    public async Task NotYamlSerializableTest()
+    {
+        const string code = """
+            using Robust.Shared.Serialization.Manager.Attributes;
+
+            [NotYamlSerializable]
+            public sealed class NotSerializableClass { }
+
+            [DataDefinition]
+            public sealed partial class Foo
+            {
+                [DataField]
+                public NotSerializableClass BadField;
+
+                [DataField]
+                public NotSerializableClass BadProperty { get; set; }
+
+                public NotSerializableClass GoodField; // Not a DataField, not a problem
+
+                public NotSerializableClass GoodProperty { get; set; } // Not a DataField, not a problem
+            }
+            """;
+
+        await Verifier(code,
+            // /0/Test0.cs(10,12): error RA0033: Data field BadField in data definition Foo is type NotSerializableClass, which is not YAML serializable
+            VerifyCS.Diagnostic(DataDefinitionAnalyzer.DataFieldYamlSerializableRule).WithSpan(10, 12, 10, 32).WithArguments("BadField", "Foo", "NotSerializableClass"),
+            // /0/Test0.cs(13,12): error RA0033: Data field BadProperty in data definition Foo is type NotSerializableClass, which is not YAML serializable
+            VerifyCS.Diagnostic(DataDefinitionAnalyzer.DataFieldYamlSerializableRule).WithSpan(13, 12, 13, 32).WithArguments("BadProperty", "Foo", "NotSerializableClass")
         );
     }
 }

Robust.Analyzers/DataDefinitionAnalyzer.cs

@@ -18,6 +18,7 @@ public sealed class DataDefinitionAnalyzer : DiagnosticAnalyzer
     private const string ImplicitDataDefinitionNamespace = "Robust.Shared.Serialization.Manager.Attributes.ImplicitDataDefinitionForInheritorsAttribute";
     private const string DataFieldBaseNamespace = "Robust.Shared.Serialization.Manager.Attributes.DataFieldBaseAttribute";
     private const string ViewVariablesNamespace = "Robust.Shared.ViewVariables.ViewVariablesAttribute";
+    private const string NotYamlSerializableName = "Robust.Shared.Serialization.Manager.Attributes.NotYamlSerializableAttribute";
     private const string DataFieldAttributeName = "DataField";
     private const string ViewVariablesAttributeName = "ViewVariables";
 
@@ -81,9 +82,19 @@ public sealed class DataDefinitionAnalyzer : DiagnosticAnalyzer
         "Make sure to remove the ViewVariables attribute."
     );
 
+    public static readonly DiagnosticDescriptor DataFieldYamlSerializableRule = new(
+        Diagnostics.IdDataFieldYamlSerializable,
+        "Data field type is not YAML serializable",
+        "Data field {0} in data definition {1} is type {2}, which is not YAML serializable",
+        "Usage",
+        DiagnosticSeverity.Error,
+        true,
+        "Make sure to use a type that is YAML serializable."
+    );
+
     public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create(
         DataDefinitionPartialRule, NestedDataDefinitionPartialRule, DataFieldWritableRule, DataFieldPropertyWritableRule,
-        DataFieldRedundantTagRule, DataFieldNoVVReadWriteRule
+        DataFieldRedundantTagRule, DataFieldNoVVReadWriteRule, DataFieldYamlSerializableRule
     );
 
     public override void Initialize(AnalysisContext context)
@@ -164,6 +175,19 @@ public sealed class DataDefinitionAnalyzer : DiagnosticAnalyzer
                 TryGetAttributeLocation(field, ViewVariablesAttributeName, out var location);
                 context.ReportDiagnostic(Diagnostic.Create(DataFieldNoVVReadWriteRule, location, fieldSymbol.Name, type.Name));
             }
+
+            if (context.SemanticModel.GetSymbolInfo(field.Declaration.Type).Symbol is not ITypeSymbol fieldTypeSymbol)
+                continue;
+
+            if (IsNotYamlSerializable(fieldSymbol, fieldTypeSymbol))
+            {
+                context.ReportDiagnostic(Diagnostic.Create(DataFieldYamlSerializableRule,
+                    (context.Node as FieldDeclarationSyntax)?.Declaration.Type.GetLocation(),
+                    fieldSymbol.Name,
+                    type.Name,
+                    fieldTypeSymbol.MetadataName
+                ));
+            }
         }
     }
 
@@ -201,6 +225,19 @@ public sealed class DataDefinitionAnalyzer : DiagnosticAnalyzer
             TryGetAttributeLocation(property, ViewVariablesAttributeName, out var location);
             context.ReportDiagnostic(Diagnostic.Create(DataFieldNoVVReadWriteRule, location, propertySymbol.Name, type.Name));
         }
+
+        if (context.SemanticModel.GetSymbolInfo(property.Type).Symbol is not ITypeSymbol propertyTypeSymbol)
+            return;
+
+        if (IsNotYamlSerializable(propertySymbol, propertyTypeSymbol))
+        {
+            context.ReportDiagnostic(Diagnostic.Create(DataFieldYamlSerializableRule,
+                (context.Node as PropertyDeclarationSyntax)?.Type.GetLocation(),
+                propertySymbol.Name,
+                type.Name,
+                propertyTypeSymbol.Name
+            ));
+        }
     }
 
     private static bool IsReadOnlyDataField(ITypeSymbol type, ISymbol field)
@@ -383,6 +420,14 @@ public sealed class DataDefinitionAnalyzer : DiagnosticAnalyzer
         return (VVAccess)accessByte == VVAccess.ReadWrite;
     }
 
+    private static bool IsNotYamlSerializable(ISymbol field, ITypeSymbol type)
+    {
+        if (!IsDataField(field, out _, out _))
+            return false;
+
+        return HasAttribute(type, NotYamlSerializableName);
+    }
+
     private static bool IsImplicitDataDefinition(ITypeSymbol type)
     {
         if (HasAttribute(type, ImplicitDataDefinitionNamespace))

Robust.Client/Animations/AnimationTrackProperty.cs

@@ -13,7 +13,7 @@ namespace Robust.Client.Animations
     /// </summary>
     public abstract class AnimationTrackProperty : AnimationTrack
     {
-        public List<KeyFrame> KeyFrames { get; protected set; } = new();
+        public List<KeyFrame> KeyFrames { get; set; } = new();
 
         /// <summary>
         ///     How to interpolate values when between two keyframes.

Robust.Client/ClientIoC.cs

@@ -10,6 +10,7 @@ using Robust.Client.Graphics;
 using Robust.Client.Graphics.Clyde;
 using Robust.Client.HWId;
 using Robust.Client.Input;
+using Robust.Client.Localization;
 using Robust.Client.Map;
 using Robust.Client.Placement;
 using Robust.Client.Player;
@@ -36,6 +37,7 @@ using Robust.Shared.Console;
 using Robust.Shared.ContentPack;
 using Robust.Shared.GameObjects;
 using Robust.Shared.IoC;
+using Robust.Shared.Localization;
 using Robust.Shared.Map;
 using Robust.Shared.Network;
 using Robust.Shared.Physics;
@@ -104,6 +106,8 @@ namespace Robust.Client
             deps.Register<IGamePrototypeLoadManager, GamePrototypeLoadManager>();
             deps.Register<NetworkResourceManager>();
             deps.Register<IReloadManager, ReloadManager>();
+            deps.Register<ILocalizationManager, ClientLocalizationManager>();
+            deps.Register<ILocalizationManagerInternal, ClientLocalizationManager>();
 
             switch (mode)
             {

Robust.Client/ComponentTrees/SpriteTreeSystem.cs

@@ -2,6 +2,7 @@ using System.Numerics;
 using Robust.Client.GameObjects;
 using Robust.Shared.ComponentTrees;
 using Robust.Shared.GameObjects;
+using Robust.Shared.IoC;
 using Robust.Shared.Maths;
 using Robust.Shared.Physics;
 
@@ -9,25 +10,7 @@ namespace Robust.Client.ComponentTrees;
 
 public sealed class SpriteTreeSystem : ComponentTreeSystem<SpriteTreeComponent, SpriteComponent>
 {
-    public override void Initialize()
-    {
-        base.Initialize();
-        SubscribeLocalEvent<SpriteComponent, QueueSpriteTreeUpdateEvent>(OnQueueUpdate);
-    }
-
-    private void OnQueueUpdate(EntityUid uid, SpriteComponent component, ref QueueSpriteTreeUpdateEvent args)
-        => QueueTreeUpdate(uid, component, args.Xform);
-
-    // TODO remove this when finally ECSing sprite components
-    [ByRefEvent]
-    internal readonly struct QueueSpriteTreeUpdateEvent
-    {
-        public readonly TransformComponent Xform;
-        public QueueSpriteTreeUpdateEvent(TransformComponent xform)
-        {
-            Xform = xform;
-        }
-    }
+    [Dependency] private readonly SpriteSystem _sprite = default!;
 
     #region Component Tree Overrides
     protected override bool DoFrameUpdate => true;
@@ -36,6 +19,11 @@ public sealed class SpriteTreeSystem : ComponentTreeSystem<SpriteTreeComponent,
     protected override int InitialCapacity => 1024;
 
     protected override Box2 ExtractAabb(in ComponentTreeEntry<SpriteComponent> entry, Vector2 pos, Angle rot)
-        => entry.Component.CalculateRotatedBoundingBox(pos, rot, default).CalcBoundingBox();
+    {
+        // TODO SPRITE optimize this
+        // Because the just take the BB of the rotated BB, I'mt pretty sure we do a lot of unnecessary maths.
+        return _sprite.CalculateBounds((entry.Uid, entry.Component), pos, rot, default).CalcBoundingBox();
+    }
+
     #endregion
 }

Robust.Client/GameController/GameController.cs

@@ -31,6 +31,7 @@ using Robust.Shared.Configuration;
 using Robust.Shared.ContentPack;
 using Robust.Shared.Exceptions;
 using Robust.Shared.IoC;
+using Robust.Shared.Localization;
 using Robust.Shared.Log;
 using Robust.Shared.Map;
 using Robust.Shared.Network;
@@ -94,6 +95,7 @@ namespace Robust.Client
         [Dependency] private readonly IReplayRecordingManagerInternal _replayRecording = default!;
         [Dependency] private readonly IReflectionManager _reflectionManager = default!;
         [Dependency] private readonly IReloadManager _reload = default!;
+        [Dependency] private readonly ILocalizationManager _loc = default!;
 
         private IWebViewManagerHook? _webViewHook;
 
@@ -158,6 +160,7 @@ namespace Robust.Client
             }
 
             _serializationManager.Initialize();
+            _loc.Initialize();
 
             // Call Init in game assemblies.
             _modLoader.BroadcastRunLevel(ModRunLevel.PreInit);

Robust.Client/GameObjects/ClientEntityManager.cs

@@ -296,7 +296,7 @@ namespace Robust.Client.GameObjects
         public override void PredictedDeleteEntity(Entity<MetaDataComponent?, TransformComponent?> ent)
         {
             if (!MetaQuery.Resolve(ent.Owner, ref ent.Comp1)
-                || ent.Comp1.EntityDeleted
+                || ent.Comp1.EntityLifeStage >= EntityLifeStage.Terminating
                 || !TransformQuery.Resolve(ent.Owner, ref ent.Comp2))
             {
                 return;
@@ -322,7 +322,7 @@ namespace Robust.Client.GameObjects
         {
             if (IsQueuedForDeletion(ent.Owner)
                 || !MetaQuery.Resolve(ent.Owner, ref ent.Comp1)
-                || ent.Comp1.EntityDeleted
+                || ent.Comp1.EntityLifeStage >= EntityLifeStage.Terminating
                 || !TransformQuery.Resolve(ent.Owner, ref ent.Comp2))
             {
                 return;

Robust.Client/GameObjects/Components/Renderable/IRenderableComponent.cs

@@ -1,9 +1,11 @@
-using Robust.Shared.GameObjects;
+using System;
+using Robust.Shared.GameObjects;
 using Robust.Shared.Map;
 using Robust.Shared.Maths;
 
 namespace Robust.Client.GameObjects
 {
+    [Obsolete]
     public partial interface IRenderableComponent : IComponent
     {
         int DrawDepth { get; set; }

Robust.Client/GameObjects/Components/Renderable/ISpriteLayer.cs

@@ -1,6 +1,5 @@
 using System.Numerics;
 using Robust.Client.Graphics;
-using Robust.Shared.Graphics;
 using Robust.Shared.Graphics.RSI;
 using Robust.Shared.Maths;
 

Robust.Client/GameObjects/Components/Renderable/SpriteBoundsOverlay.cs

@@ -24,9 +24,7 @@ namespace Robust.Client.GameObjects
 
     public sealed class SpriteBoundsSystem : EntitySystem
     {
-        [Dependency] private readonly SharedTransformSystem _xformSystem = default!;
         [Dependency] private readonly IOverlayManager _overlayManager = default!;
-        [Dependency] private readonly SpriteTreeSystem _spriteTree = default!;
 
         private SpriteBoundsOverlay? _overlay;
 
@@ -42,7 +40,7 @@ namespace Robust.Client.GameObjects
                 if (_enabled)
                 {
                     DebugTools.AssertNull(_overlay);
-                    _overlay = new SpriteBoundsOverlay(_spriteTree, _xformSystem);
+                    _overlay = new SpriteBoundsOverlay(EntityManager);
                     _overlayManager.AddOverlay(_overlay);
                 }
                 else
@@ -57,18 +55,13 @@ namespace Robust.Client.GameObjects
         private bool _enabled;
     }
 
-    public sealed class SpriteBoundsOverlay : Overlay
+    public sealed class SpriteBoundsOverlay(IEntityManager entMan) : Overlay
     {
         public override OverlaySpace Space => OverlaySpace.WorldSpace;
 
-        private readonly SharedTransformSystem _xformSystem;
-        private SpriteTreeSystem _renderTree;
-
-        public SpriteBoundsOverlay(SpriteTreeSystem renderTree, SharedTransformSystem xformSystem)
-        {
-            _renderTree = renderTree;
-            _xformSystem = xformSystem;
-        }
+        private readonly SharedTransformSystem _xformSystem = entMan.System<SharedTransformSystem>();
+        private readonly SpriteSystem _spriteSystem = entMan.System<SpriteSystem>();
+        private readonly SpriteTreeSystem _renderTree = entMan.System<SpriteTreeSystem>();
 
         protected internal override void Draw(in OverlayDrawArgs args)
         {
@@ -76,10 +69,11 @@ namespace Robust.Client.GameObjects
             var currentMap = args.MapId;
             var viewport = args.WorldBounds;
 
-            foreach (var (sprite, xform) in _renderTree.QueryAabb(currentMap, viewport))
+            foreach (var entry in _renderTree.QueryAabb(currentMap, viewport))
             {
+                var (sprite, xform) = entry;
                 var (worldPos, worldRot) = _xformSystem.GetWorldPositionRotation(xform);
-                var bounds = sprite.CalculateRotatedBoundingBox(worldPos, worldRot, args.Viewport.Eye?.Rotation ?? default);
+                var bounds = _spriteSystem.CalculateBounds((entry.Uid, sprite), worldPos, worldRot, args.Viewport.Eye?.Rotation ?? default);
 
                 // Get scaled down bounds used to indicate the "south" of a sprite.
                 var localBound = bounds.Box;

Robust.Client/GameObjects/EntitySystems/AnimationPlayerSystem.cs

@@ -14,7 +14,9 @@ namespace Robust.Client.GameObjects
         private EntityQuery<AnimationPlayerComponent> _playerQuery;
         private EntityQuery<MetaDataComponent> _metaQuery;
 
+#pragma warning disable CS0414
         [Dependency] private readonly IComponentFactory _compFact = default!;
+#pragma warning restore CS0414
 
         public override void Initialize()
         {

Robust.Client/GameObjects/EntitySystems/ContainerSystem.cs

@@ -1,15 +1,14 @@
-using System;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
 using Robust.Shared.Collections;
 using Robust.Shared.Containers;
 using Robust.Shared.GameObjects;
 using Robust.Shared.GameStates;
 using Robust.Shared.IoC;
 using Robust.Shared.Map;
-using Robust.Shared.Utility;
-using System.Collections.Generic;
-using System.Diagnostics.CodeAnalysis;
-using System.Linq;
 using Robust.Shared.Serialization;
+using Robust.Shared.Utility;
 using static Robust.Shared.Containers.ContainerManagerComponent;
 
 namespace Robust.Client.GameObjects
@@ -58,7 +57,7 @@ namespace Robust.Client.GameObjects
             if (!RemoveExpectedEntity(meta.NetEntity, out var container))
                 return;
 
-            Insert((uid, TransformQuery.GetComponent(uid), MetaQuery.GetComponent(uid), null), container);
+            Insert((uid, TransformQuery.GetComponent(uid), MetaQuery.GetComponent(uid), null), container, force: true);
         }
 
         public override void ShutdownContainer(BaseContainer container)
@@ -232,7 +231,7 @@ namespace Robust.Client.GameObjects
                 return;
             }
 
-            Insert(message.Entity, container);
+            Insert(message.Entity, container, force: true);
         }
 
         public void AddExpectedEntity(NetEntity netEntity, BaseContainer container)

Robust.Client/GameObjects/EntitySystems/PointLightSystem.cs

@@ -16,6 +16,7 @@ namespace Robust.Client.GameObjects
         public override void Initialize()
         {
             base.Initialize();
+            SubscribeLocalEvent<PointLightComponent, ComponentGetState>(OnLightGetState);
             SubscribeLocalEvent<PointLightComponent, ComponentInit>(HandleInit);
             SubscribeLocalEvent<PointLightComponent, ComponentHandleState>(OnLightHandleState);
         }

Robust.Client/GameObjects/EntitySystems/SpriteSystem.Bounds.cs

@@ -0,0 +1,149 @@
+using System;
+using System.Linq;
+using System.Numerics;
+using Robust.Client.Graphics;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Graphics.RSI;
+using Robust.Shared.Maths;
+using Robust.Shared.Utility;
+using static Robust.Client.GameObjects.SpriteComponent;
+
+namespace Robust.Client.GameObjects;
+
+// This partial class contains code related to updating a sprites bounding boxes and its position in the sprite tree.
+public sealed partial class SpriteSystem
+{
+    /// <summary>
+    /// Get a sprite's local bounding box. The returned bounds do factor in the sprite's scale but not the rotation or
+    /// offset.
+    /// </summary>
+    public Box2 GetLocalBounds(Entity<SpriteComponent> sprite)
+    {
+        if (!sprite.Comp.BoundsDirty)
+        {
+            DebugTools.Assert(sprite.Comp.Layers.All(x => !x.BoundsDirty || !x.Drawn));
+            return sprite.Comp._bounds;
+        }
+
+        var bounds = new Box2();
+        foreach (var layer in sprite.Comp.Layers)
+        {
+            if (layer.Drawn)
+                bounds = bounds.Union(GetLocalBounds(layer));
+        }
+
+        sprite.Comp._bounds = bounds;
+        sprite.Comp.BoundsDirty = false;
+        return sprite.Comp._bounds;
+    }
+
+    /// <summary>
+    /// Get a layer's local bounding box relative to its owning sprite. Unlike the sprite variant of this method, this
+    /// does account for the layer's rotation and offset.
+    /// </summary>
+    public Box2 GetLocalBounds(Layer layer)
+    {
+        if (!layer.BoundsDirty)
+        {
+            DebugTools.Assert(layer.Bounds.EqualsApprox(CalculateLocalBounds(layer)));
+            return layer.Bounds;
+        }
+
+        layer.Bounds = CalculateLocalBounds(layer);
+        layer.BoundsDirty = false;
+        return layer.Bounds;
+    }
+
+    internal Box2 CalculateLocalBounds(Layer layer)
+    {
+        var textureSize = (Vector2) layer.PixelSize / EyeManager.PixelsPerMeter;
+        var longestSide = MathF.Max(textureSize.X, textureSize.Y);
+        var longestRotatedSide = Math.Max(longestSide, (textureSize.X + textureSize.Y) / MathF.Sqrt(2));
+
+        Vector2 size;
+        var sprite = layer.Owner.Comp;
+
+        // If this layer has any form of arbitrary rotation, return a bounding box big enough to cover
+        // any possible rotation.
+        if (layer._rotation != 0)
+        {
+            size = new Vector2(longestRotatedSide, longestRotatedSide);
+            return Box2.CenteredAround(layer.Offset, size * layer._scale);
+        }
+
+        var snapToCardinals = sprite.SnapCardinals;
+        if (sprite.GranularLayersRendering && layer.RenderingStrategy != LayerRenderingStrategy.UseSpriteStrategy)
+        {
+            snapToCardinals = layer.RenderingStrategy == LayerRenderingStrategy.SnapToCardinals;
+        }
+
+        if (snapToCardinals)
+        {
+            // Snapping to cardinals only makes sense for 1-directional layers/sprites
+            DebugTools.Assert(layer._actualState == null || layer._actualState.RsiDirections == RsiDirectionType.Dir1);
+
+            // We won't know the actual direction it snaps to, so we ahve to assume the box is given by the longest side.
+            size = new Vector2(longestSide, longestSide);
+            return Box2.CenteredAround(layer.Offset, size * layer._scale);
+        }
+
+        // Build the bounding box based on how many directions the sprite has
+        size = (layer._actualState?.RsiDirections) switch
+        {
+            RsiDirectionType.Dir4 => new Vector2(longestSide, longestSide),
+            RsiDirectionType.Dir8 => new Vector2(longestRotatedSide, longestRotatedSide),
+            _ => textureSize
+        };
+
+        return Box2.CenteredAround(layer.Offset, size * layer._scale);
+    }
+
+    /// <summary>
+    /// Gets a sprite's bounding box in world coordinates.
+    /// </summary>
+    public Box2Rotated CalculateBounds(Entity<SpriteComponent> sprite, Vector2 worldPos, Angle worldRot, Angle eyeRot)
+    {
+        // fast check for invisible sprites
+        if (!sprite.Comp.Visible || sprite.Comp.Layers.Count == 0)
+            return new Box2Rotated(new Box2(worldPos, worldPos), Angle.Zero, worldPos);
+
+        // We need to modify world rotation so that it lies between 0 and 2pi.
+        // This matters for 4 or 8 directional sprites deciding which quadrant (octant?) they lie in.
+        // the 0->2pi convention is set by the sprite-rendering code that selects the layers.
+        // See RenderInternal().
+
+        worldRot = worldRot.Reduced();
+        if (worldRot.Theta < 0)
+            worldRot = new Angle(worldRot.Theta + Math.Tau);
+
+        // Next, what we do is take the box2 and apply the sprite's transform, and then the entity's transform. We
+        // could do this via Matrix3.TransformBox, but that only yields bounding boxes. So instead we manually
+        // transform our box by the combination of these matrices:
+
+        var finalRotation = sprite.Comp.NoRotation
+            ? sprite.Comp.Rotation - eyeRot
+            : sprite.Comp.Rotation + worldRot;
+
+        var bounds = GetLocalBounds(sprite);
+
+        // slightly faster path if offset == 0 (true for 99.9% of sprites)
+        if (sprite.Comp.Offset == Vector2.Zero)
+            return new Box2Rotated(bounds.Translated(worldPos), finalRotation, worldPos);
+
+        var adjustedOffset = sprite.Comp.NoRotation
+            ? (-eyeRot).RotateVec(sprite.Comp.Offset)
+            : worldRot.RotateVec(sprite.Comp.Offset);
+
+        var position = adjustedOffset + worldPos;
+        return new Box2Rotated(bounds.Translated(position), finalRotation, position);
+    }
+
+    private void DirtyBounds(Entity<SpriteComponent> sprite)
+    {
+        sprite.Comp.BoundsDirty = true;
+        foreach (var layer in sprite.Comp.Layers)
+        {
+            layer.BoundsDirty = true;
+        }
+    }
+}

Robust.Client/GameObjects/EntitySystems/SpriteSystem.Component.cs

@@ -1,4 +1,8 @@
-using System.Linq;
+using System;
+using System.Collections.Generic;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Maths;
+using Robust.Shared.Utility;
 
 namespace Robust.Client.GameObjects;
 
@@ -41,4 +45,66 @@ public sealed partial class SpriteSystem
         layer.AnimationTimeLeft = (float) -(time % state.TotalDelay);
         layer.AnimationFrame = 0;
     }
+
+    public void CopySprite(Entity<SpriteComponent?> source, Entity<SpriteComponent?> target)
+    {
+        if (!Resolve(source.Owner, ref source.Comp))
+            return;
+
+        if (!Resolve(target.Owner, ref target.Comp))
+            return;
+
+        target.Comp._baseRsi = source.Comp._baseRsi;
+        target.Comp._bounds = source.Comp._bounds;
+        target.Comp._visible = source.Comp._visible;
+        target.Comp.color = source.Comp.color;
+        target.Comp.offset = source.Comp.offset;
+        target.Comp.rotation = source.Comp.rotation;
+        target.Comp.scale = source.Comp.scale;
+        target.Comp.LocalMatrix = Matrix3Helpers.CreateTransform(
+            in target.Comp.offset,
+            in target.Comp.rotation,
+            in target
+            .Comp.scale);
+
+        target.Comp.drawDepth = source.Comp.drawDepth;
+        target.Comp.NoRotation = source.Comp.NoRotation;
+        target.Comp.DirectionOverride = source.Comp.DirectionOverride;
+        target.Comp.EnableDirectionOverride = source.Comp.EnableDirectionOverride;
+        target.Comp.Layers = new List<SpriteComponent.Layer>(source.Comp.Layers.Count);
+        foreach (var otherLayer in source.Comp.Layers)
+        {
+            var layer = new SpriteComponent.Layer(otherLayer, target.Comp);
+            layer.Index = target.Comp.Layers.Count;
+            layer.Owner = target!;
+            target.Comp.Layers.Add(layer);
+        }
+
+        target.Comp.IsInert = source.Comp.IsInert;
+        target.Comp.LayerMap = source.Comp.LayerMap.ShallowClone();
+        target.Comp.PostShader = source.Comp.PostShader is {Mutable: true}
+            ? source.Comp.PostShader.Duplicate()
+            : source.Comp.PostShader;
+
+        target.Comp.RenderOrder = source.Comp.RenderOrder;
+        target.Comp.GranularLayersRendering = source.Comp.GranularLayersRendering;
+
+        DirtyBounds(target!);
+        _tree.QueueTreeUpdate(target!);
+    }
+
+    /// <summary>
+    /// Adds a sprite to a queue that will update <see cref="SpriteComponent.IsInert"/> next frame.
+    /// </summary>
+    public void QueueUpdateIsInert(Entity<SpriteComponent> sprite)
+    {
+        if (sprite.Comp._inertUpdateQueued)
+            return;
+
+        sprite.Comp._inertUpdateQueued = true;
+        _inertUpdateQueue.Enqueue(sprite);
+    }
+
+    [Obsolete("Use QueueUpdateIsInert")]
+    public void QueueUpdateInert(EntityUid uid, SpriteComponent sprite) => QueueUpdateIsInert(new (uid, sprite));
 }

Robust.Client/GameObjects/EntitySystems/SpriteSystem.Helpers.cs

@@ -1,11 +1,153 @@
+using System;
+using System.Collections.Generic;
 using System.Numerics;
+using JetBrains.Annotations;
+using Robust.Client.Graphics;
+using Robust.Client.ResourceManagement;
 using Robust.Shared.GameObjects;
 using Robust.Shared.Map;
+using Robust.Shared.Prototypes;
+using Robust.Shared.Utility;
 
 namespace Robust.Client.GameObjects;
 
+// This partial class contains various public helper methods, including methods for extracting textures/icons from
+// sprite specifiers and entity prototypes.
 public sealed partial class SpriteSystem
 {
+    private readonly Dictionary<string, IRsiStateLike> _cachedPrototypeIcons = new();
+
+    public Texture Frame0(EntityPrototype prototype)
+    {
+        return GetPrototypeIcon(prototype).Default;
+    }
+
+    public Texture Frame0(SpriteSpecifier specifier)
+    {
+        return RsiStateLike(specifier).Default;
+    }
+
+    public IRsiStateLike RsiStateLike(SpriteSpecifier specifier)
+    {
+        switch (specifier)
+        {
+            case SpriteSpecifier.Texture tex:
+                return GetTexture(tex);
+
+            case SpriteSpecifier.Rsi rsi:
+                return GetState(rsi);
+
+            case SpriteSpecifier.EntityPrototype prototypeIcon:
+                return GetPrototypeIcon(prototypeIcon.EntityPrototypeId);
+
+            default:
+                throw new NotSupportedException();
+        }
+    }
+
+    public Texture GetIcon(IconComponent icon)
+    {
+        return GetState(icon.Icon).Frame0;
+    }
+
+    /// <summary>
+    ///     Returns an icon for a given <see cref="EntityPrototype"/> ID, or a fallback in case of an error.
+    ///     This method caches the result based on the prototype identifier.
+    /// </summary>
+    public IRsiStateLike GetPrototypeIcon(string prototype)
+    {
+        // Check if this prototype has been cached before, and if so return the result.
+        if (_cachedPrototypeIcons.TryGetValue(prototype, out var cachedResult))
+            return cachedResult;
+
+        if (!_proto.TryIndex<EntityPrototype>(prototype, out var entityPrototype))
+        {
+            // The specified prototype doesn't exist, return the fallback "error" sprite.
+            _sawmill.Error("Failed to load PrototypeIcon {0}", prototype);
+            return GetFallbackState();
+        }
+
+        // Generate the icon and cache it in case it's ever needed again.
+        var result = GetPrototypeIcon(entityPrototype);
+        _cachedPrototypeIcons[prototype] = result;
+
+        return result;
+    }
+
+    /// <summary>
+    ///     Returns an icon for a given <see cref="EntityPrototype"/> ID, or a fallback in case of an error.
+    ///     This method does NOT cache the result.
+    /// </summary>
+    public IRsiStateLike GetPrototypeIcon(EntityPrototype prototype)
+    {
+        // IconComponent takes precedence. If it has a valid icon, return that. Otherwise, continue as normal.
+        if (prototype.Components.TryGetValue("Icon", out var compData)
+            && compData.Component is IconComponent icon)
+        {
+            return GetIcon(icon);
+        }
+
+        // If the prototype doesn't have a SpriteComponent, then there's nothing we can do but return the fallback.
+        if (!prototype.Components.ContainsKey("Sprite"))
+        {
+            return GetFallbackState();
+        }
+
+        // Finally, we use spawn a dummy entity to get its icon.
+        var dummy = Spawn(prototype.ID, MapCoordinates.Nullspace);
+        var spriteComponent = EnsureComp<SpriteComponent>(dummy);
+        var result = spriteComponent.Icon ?? GetFallbackState();
+        Del(dummy);
+
+        return result;
+    }
+
+    [Pure]
+    public RSI.State GetFallbackState()
+    {
+        return _resourceCache.GetFallback<RSIResource>().RSI["error"];
+    }
+
+    public Texture GetFallbackTexture()
+    {
+        return _resourceCache.GetFallback<TextureResource>().Texture;
+    }
+
+    [Pure]
+    public RSI.State GetState(SpriteSpecifier.Rsi rsiSpecifier)
+    {
+        if (_resourceCache.TryGetResource<RSIResource>(
+                TextureRoot / rsiSpecifier.RsiPath,
+                out var theRsi) &&
+            theRsi.RSI.TryGetState(rsiSpecifier.RsiState, out var state))
+        {
+            return state;
+        }
+
+        _sawmill.Error("Failed to load RSI {0}", rsiSpecifier.RsiPath);
+        return GetFallbackState();
+    }
+
+    public Texture GetTexture(SpriteSpecifier.Texture texSpecifier)
+    {
+        return _resourceCache
+            .GetResource<TextureResource>(TextureRoot / texSpecifier.TexturePath)
+            .Texture;
+    }
+
+    private void OnPrototypesReloaded(PrototypesReloadedEventArgs args)
+    {
+        if (!args.TryGetModified<EntityPrototype>(out var modified))
+            return;
+
+        // Remove all changed prototypes from the cache, if they're there.
+        foreach (var prototype in modified)
+        {
+            // Let's be lazy and not regenerate them until something needs them again.
+            _cachedPrototypeIcons.Remove(prototype);
+        }
+    }
+
     /// <summary>
     /// Gets an entity's sprite position in world terms.
     /// </summary>

Robust.Client/GameObjects/EntitySystems/SpriteSystem.Layer.cs

@@ -0,0 +1,257 @@
+using System;
+using System.Diagnostics.CodeAnalysis;
+using Robust.Client.Graphics;
+using Robust.Client.ResourceManagement;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Utility;
+using static Robust.Client.GameObjects.SpriteComponent;
+
+namespace Robust.Client.GameObjects;
+
+// This partial class contains various public methods for managing a sprite's layers.
+// This setter methods for modifying a layer's properties are in a separate file.
+public sealed partial class SpriteSystem
+{
+    public bool LayerExists(Entity<SpriteComponent?> sprite, int index)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return false;
+
+        return index > 0 && index < sprite.Comp.Layers.Count;
+    }
+
+    public bool TryGetLayer(
+        Entity<SpriteComponent?> sprite,
+        int index,
+        [NotNullWhen(true)] out Layer? layer,
+        bool logMissing)
+    {
+        layer = null;
+
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp, logMissing))
+            return false;
+
+        if (index >= 0 && index < sprite.Comp.Layers.Count)
+        {
+            layer = sprite.Comp.Layers[index];
+            DebugTools.AssertEqual(layer.Owner, sprite!);
+            DebugTools.AssertEqual(layer.Index, index);
+            return true;
+        }
+
+        if (logMissing)
+            Log.Error($"Layer index '{index}' on entity {ToPrettyString(sprite)} does not exist! Trace:\n{Environment.StackTrace}");
+
+        return false;
+    }
+
+    public bool RemoveLayer(Entity<SpriteComponent?> sprite, int index, bool logMissing = true)
+    {
+        return RemoveLayer(sprite.Owner, index, out _, logMissing);
+    }
+
+    public bool RemoveLayer(
+        Entity<SpriteComponent?> sprite,
+        int index,
+        [NotNullWhen(true)] out Layer? layer,
+        bool logMissing = true)
+    {
+        layer = null;
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp, logMissing))
+            return false;
+
+        if (!TryGetLayer(sprite, index, out layer, logMissing))
+            return false;
+
+        sprite.Comp.Layers.RemoveAt(index);
+
+        foreach (var otherLayer in sprite.Comp.Layers[index..])
+        {
+            otherLayer.Index--;
+        }
+
+        // TODO SPRITE track inverse-mapping?
+        foreach (var (key, value) in sprite.Comp.LayerMap)
+        {
+            if (value == index)
+                sprite.Comp.LayerMap.Remove(key);
+            else if (value > index)
+            {
+                sprite.Comp.LayerMap[key]--;
+            }
+        }
+
+        layer.Owner = default;
+        layer.Index = -1;
+
+#if DEBUG
+        foreach (var otherLayer in sprite.Comp.Layers)
+        {
+            DebugTools.AssertEqual(otherLayer, sprite.Comp.Layers[otherLayer.Index]);
+        }
+#endif
+
+        sprite.Comp.BoundsDirty = true;
+        _tree.QueueTreeUpdate(sprite!);
+        QueueUpdateIsInert(sprite!);
+        return true;
+    }
+
+    #region AddLayer
+
+    /// <summary>
+    /// Add the given sprite layer. If an index is specified, this will insert the layer with the given index, resulting
+    /// in all other layers being reshuffled.
+    /// </summary>
+    public int AddLayer(Entity<SpriteComponent?> sprite, Layer layer, int? index = null)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+        {
+            layer.Index = -1;
+            layer.Owner = default;
+            return -1;
+        }
+
+        layer.Owner = sprite!;
+
+        if (index is { } i && i != sprite.Comp.Layers.Count)
+        {
+            foreach (var otherLayer in sprite.Comp.Layers[i..])
+            {
+                otherLayer.Index++;
+            }
+
+            // TODO SPRITE track inverse-mapping?
+            sprite.Comp.Layers.Insert(i, layer);
+            layer.Index = i;
+
+            foreach (var (key, value) in sprite.Comp.LayerMap)
+            {
+                if (value >= i)
+                    sprite.Comp.LayerMap[key]++;
+            }
+        }
+        else
+        {
+            layer.Index = sprite.Comp.Layers.Count;
+            sprite.Comp.Layers.Add(layer);
+        }
+
+#if DEBUG
+        foreach (var otherLayer in sprite.Comp.Layers)
+        {
+            DebugTools.AssertEqual(otherLayer, sprite.Comp.Layers[otherLayer.Index]);
+        }
+#endif
+
+        layer.BoundsDirty = true;
+        if (!layer.Blank)
+        {
+            sprite.Comp.BoundsDirty = true;
+            _tree.QueueTreeUpdate(sprite!);
+            QueueUpdateIsInert(sprite!);
+        }
+        return layer.Index;
+    }
+
+    /// <summary>
+    /// Add a layer corresponding to the given RSI state.
+    /// </summary>
+    /// <param name="sprite">The sprite</param>
+    /// <param name="stateId">The RSI state</param>
+    /// <param name="rsi">The RSI to use. If not specified, it will default to using <see cref="SpriteComponent.BaseRSI"/></param>
+    /// <param name="index">The layer index to use for the new sprite.</param>
+    /// <returns></returns>
+    public int AddRsiLayer(Entity<SpriteComponent?> sprite, RSI.StateId stateId, RSI? rsi = null, int? index = null)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return -1;
+
+        var layer = AddBlankLayer(sprite!, index);
+
+        if (rsi != null)
+            LayerSetRsi(layer, rsi, stateId);
+        else
+            LayerSetRsiState(layer, stateId);
+
+        return layer.Index;
+    }
+
+    /// <summary>
+    /// Add a layer corresponding to the given RSI state.
+    /// </summary>
+    /// <param name="sprite">The sprite</param>
+    /// <param name="state">The RSI state</param>
+    /// <param name="path">The path to the RSI.</param>
+    /// <param name="index">The layer index to use for the new sprite.</param>
+    /// <returns></returns>
+    public int AddRsiLayer(Entity<SpriteComponent?> sprite, RSI.StateId state, ResPath path, int? index = null)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return -1;
+
+        if (!_resourceCache.TryGetResource<RSIResource>(TextureRoot / path, out var res))
+            Log.Error($"Unable to load RSI '{path}'. Trace:\n{Environment.StackTrace}");
+
+        if (path.Extension != "rsi")
+            Log.Error($"Expected rsi path but got '{path}'?");
+
+        return AddRsiLayer(sprite, state, res?.RSI, index);
+    }
+
+    public int AddTextureLayer(Entity<SpriteComponent?> sprite, ResPath path, int? index = null)
+    {
+        if (_resourceCache.TryGetResource<TextureResource>(TextureRoot / path, out var texture))
+            return AddTextureLayer(sprite, texture?.Texture, index);
+
+        if (path.Extension == "rsi")
+            Log.Error($"Expected texture but got rsi '{path}', did you mean 'sprite:' instead of 'texture:'?");
+
+        Log.Error($"Unable to load texture '{path}'. Trace:\n{Environment.StackTrace}");
+        return AddTextureLayer(sprite, texture?.Texture, index);
+    }
+
+    public int AddTextureLayer(Entity<SpriteComponent?> sprite, Texture? texture, int? index = null)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return -1;
+
+        var layer = new Layer {Texture = texture};
+        return AddLayer(sprite, layer, index);
+    }
+
+    public int AddLayer(Entity<SpriteComponent?> sprite, SpriteSpecifier specifier, int? newIndex = null)
+    {
+        return specifier switch
+        {
+            SpriteSpecifier.Texture tex => AddTextureLayer(sprite, tex.TexturePath, newIndex),
+            SpriteSpecifier.Rsi rsi => AddRsiLayer(sprite, rsi.RsiState, rsi.RsiPath, newIndex),
+            _ => throw new NotImplementedException()
+        };
+    }
+
+    /// <summary>
+    /// Add a new sprite layer and populate it using the provided layer data.
+    /// </summary>
+    public int AddLayer(Entity<SpriteComponent?> sprite, PrototypeLayerData layerDatum, int? index)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return -1;
+
+        var layer = AddBlankLayer(sprite!, index);
+        LayerSetData(layer, layerDatum);
+        return layer.Index;
+    }
+
+    /// <summary>
+    /// Add a blank sprite layer.
+    /// </summary>
+    public Layer AddBlankLayer(Entity<SpriteComponent> sprite, int? index = null)
+    {
+        var layer = new Layer();
+        AddLayer(sprite!, layer, index);
+        return layer;
+    }
+
+    #endregion
+}

Robust.Client/GameObjects/EntitySystems/SpriteSystem.LayerGetters.cs

@@ -0,0 +1,150 @@
+using System;
+using Robust.Client.Graphics;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Graphics.RSI;
+using static Robust.Client.GameObjects.SpriteComponent;
+using static Robust.Client.Graphics.RSI;
+
+namespace Robust.Client.GameObjects;
+
+// This partial class contains various public methods for reading a layer's properties
+public sealed partial class SpriteSystem
+{
+    #region RsiState
+
+    /// <summary>
+    /// Get the RSI state being used by the current layer. Note that the return value may be an invalid state. E.g.,
+    /// this might be a texture layer that does not use RSIs.
+    /// </summary>
+    public StateId LayerGetRsiState(Entity<SpriteComponent?> sprite, int index)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            return layer.StateId;
+
+        return StateId.Invalid;
+    }
+
+    /// <summary>
+    /// Get the RSI state being used by the current layer. Note that the return value may be an invalid state. E.g.,
+    /// this might be a texture layer that does not use RSIs.
+    /// </summary>
+    public StateId LayerGetRsiState(Entity<SpriteComponent?> sprite, string key, StateId state)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            return layer.StateId;
+
+        return StateId.Invalid;
+    }
+
+    /// <summary>
+    /// Get the RSI state being used by the current layer. Note that the return value may be an invalid state. E.g.,
+    /// this might be a texture layer that does not use RSIs.
+    /// </summary>
+    public StateId LayerGetRsiState(Entity<SpriteComponent?> sprite, Enum key, StateId state)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            return layer.StateId;
+
+        return StateId.Invalid;
+    }
+
+    #endregion
+
+    #region RsiState
+
+    /// <summary>
+    /// Returns the RSI being used by the layer to resolve it's RSI state. If the layer does not specify an RSI, this
+    /// will just be the base RSI of the owning sprite (<see cref="SpriteComponent.BaseRSI"/>).
+    /// </summary>
+    public RSI? LayerGetEffectiveRsi(Entity<SpriteComponent?> sprite, int index)
+    {
+        TryGetLayer(sprite, index, out var layer, true);
+        return layer?.ActualRsi;
+    }
+
+    /// <summary>
+    /// Returns the RSI being used by the layer to resolve it's RSI state. If the layer does not specify an RSI, this
+    /// will just be the base RSI of the owning sprite (<see cref="SpriteComponent.BaseRSI"/>).
+    /// </summary>
+    public RSI? LayerGetEffectiveRsi(Entity<SpriteComponent?> sprite, string key, StateId state)
+    {
+        TryGetLayer(sprite, key, out var layer, true);
+        return layer?.ActualRsi;
+    }
+
+    /// <summary>
+    /// Returns the RSI being used by the layer to resolve it's RSI state. If the layer does not specify an RSI, this
+    /// will just be the base RSI of the owning sprite (<see cref="SpriteComponent.BaseRSI"/>).
+    /// </summary>
+    public RSI? LayerGetEffectiveRsi(Entity<SpriteComponent?> sprite, Enum key, StateId state)
+    {
+        TryGetLayer(sprite, key, out var layer, true);
+        return layer?.ActualRsi;
+    }
+
+    #endregion
+
+    #region Directions
+
+    public RsiDirectionType LayerGetDirections(Entity<SpriteComponent?> sprite, int index)
+    {
+        return TryGetLayer(sprite, index, out var layer, true)
+            ? LayerGetDirections(layer)
+            : RsiDirectionType.Dir1;
+    }
+
+
+    public RsiDirectionType LayerGetDirections(Entity<SpriteComponent?> sprite, Enum key)
+    {
+        return TryGetLayer(sprite, key, out var layer, true)
+            ? LayerGetDirections(layer)
+            : RsiDirectionType.Dir1;
+    }
+
+    public RsiDirectionType LayerGetDirections(Entity<SpriteComponent?> sprite, string key)
+    {
+        return TryGetLayer(sprite, key, out var layer, true)
+            ? LayerGetDirections(layer)
+            : RsiDirectionType.Dir1;
+    }
+
+    public RsiDirectionType LayerGetDirections(Layer layer)
+    {
+        if (!layer.StateId.IsValid)
+            return RsiDirectionType.Dir1;
+
+        // Pull texture from RSI state instead.
+        if (layer.ActualRsi is not {} rsi || !rsi.TryGetState(layer.StateId, out var state))
+            return RsiDirectionType.Dir1;
+
+        return state.RsiDirections;
+    }
+
+    public int LayerGetDirectionCount(Entity<SpriteComponent?> sprite, int index)
+    {
+        return TryGetLayer(sprite, index, out var layer, true) ? LayerGetDirectionCount(layer) : 1;
+    }
+
+    public int LayerGetDirectionCount(Entity<SpriteComponent?> sprite, Enum key)
+    {
+        return TryGetLayer(sprite, key, out var layer, true) ? LayerGetDirectionCount(layer) : 1;
+    }
+
+    public int LayerGetDirectionCount(Entity<SpriteComponent?> sprite, string key)
+    {
+        return TryGetLayer(sprite, key, out var layer, true) ? LayerGetDirectionCount(layer) : 1;
+    }
+
+    public int LayerGetDirectionCount(Layer layer)
+    {
+        return LayerGetDirections(layer) switch
+        {
+            RsiDirectionType.Dir1 => 1,
+            RsiDirectionType.Dir4 => 4,
+            RsiDirectionType.Dir8 => 8,
+            _ => throw new ArgumentOutOfRangeException()
+        };
+    }
+
+    #endregion
+}

Robust.Client/GameObjects/EntitySystems/SpriteSystem.LayerMap.cs

@@ -0,0 +1,299 @@
+using System;
+using System.Diagnostics.CodeAnalysis;
+using Robust.Shared.GameObjects;
+using static Robust.Client.GameObjects.SpriteComponent;
+
+namespace Robust.Client.GameObjects;
+
+// This partial class contains various public methods for manipulating layer mappings.
+public sealed partial class SpriteSystem
+{
+    /// <summary>
+    /// Map an enum to a layer index.
+    /// </summary>
+    public void LayerMapSet(Entity<SpriteComponent?> sprite, Enum key, int index)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return;
+
+        if (index < 0 || index >= sprite.Comp.Layers.Count)
+            throw new ArgumentOutOfRangeException(nameof(index));
+
+        sprite.Comp.LayerMap[key] = index;
+    }
+
+    /// <summary>
+    /// Map string to a layer index. If possible, it is preferred to use an enum key.
+    /// string keys mainly exist to make it easier to define custom layer keys in yaml.
+    /// </summary>
+    public void LayerMapSet(Entity<SpriteComponent?> sprite, string key, int index)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return;
+
+        if (index < 0 || index >= sprite.Comp.Layers.Count)
+            throw new ArgumentOutOfRangeException(nameof(index));
+
+        sprite.Comp.LayerMap[key] = index;
+    }
+
+    /// <summary>
+    /// Map an enum to a layer index.
+    /// </summary>
+    public void LayerMapAdd(Entity<SpriteComponent?> sprite, Enum key, int index)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return;
+
+        if (index < 0 || index >= sprite.Comp.Layers.Count)
+            throw new ArgumentOutOfRangeException(nameof(index));
+
+        sprite.Comp.LayerMap.Add(key, index);
+    }
+
+    /// <summary>
+    /// Map a string to a layer index. If possible, it is preferred to use an enum key.
+    /// string keys mainly exist to make it easier to define custom layer keys in yaml.
+    /// </summary>
+    public void LayerMapAdd(Entity<SpriteComponent?> sprite, string key, int index)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return;
+
+        if (index < 0 || index >= sprite.Comp.Layers.Count)
+            throw new ArgumentOutOfRangeException(nameof(index));
+
+        sprite.Comp.LayerMap.Add(key, index);
+    }
+
+    /// <summary>
+    /// Remove an enum mapping.
+    /// </summary>
+    public bool LayerMapRemove(Entity<SpriteComponent?> sprite, Enum key)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return false;
+
+        return sprite.Comp.LayerMap.Remove(key);
+    }
+
+    /// <summary>
+    /// Remove a string mapping.
+    /// </summary>
+    public bool LayerMapRemove(Entity<SpriteComponent?> sprite, string key)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return false;
+
+        return sprite.Comp.LayerMap.Remove(key);
+    }
+
+    /// <summary>
+    /// Remove an enum mapping.
+    /// </summary>
+    public bool LayerMapRemove(Entity<SpriteComponent?> sprite, Enum key, out int index)
+    {
+        if (_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return sprite.Comp.LayerMap.Remove(key, out index);
+
+        index = 0;
+        return false;
+    }
+
+    /// <summary>
+    /// Remove a string mapping.
+    /// </summary>
+    public bool LayerMapRemove(Entity<SpriteComponent?> sprite, string key, out int index)
+    {
+        if (_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return sprite.Comp.LayerMap.Remove(key, out index);
+
+        index = 0;
+        return false;
+    }
+
+    /// <summary>
+    /// Attempt to resolve an enum mapping.
+    /// </summary>
+    public bool LayerMapTryGet(Entity<SpriteComponent?> sprite, Enum key, out int index, bool logMissing)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp, logMissing))
+        {
+            index = 0;
+            return false;
+        }
+
+        if (sprite.Comp.LayerMap.TryGetValue(key, out index))
+            return true;
+
+        if (logMissing)
+            Log.Error($"Layer with key '{key}' does not exist on entity {ToPrettyString(sprite)}! Trace:\n{Environment.StackTrace}");
+
+        return false;
+    }
+
+    /// <summary>
+    /// Attempt to resolve a string mapping.
+    /// </summary>
+    public bool LayerMapTryGet(Entity<SpriteComponent?> sprite, string key, out int index, bool logMissing)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp, logMissing))
+        {
+            index = 0;
+            return false;
+        }
+
+        if (sprite.Comp.LayerMap.TryGetValue(key, out index))
+            return true;
+
+        if (logMissing)
+            Log.Error($"Layer with key '{key}' does not exist on entity {ToPrettyString(sprite)}! Trace:\n{Environment.StackTrace}");
+
+        return false;
+    }
+
+    /// <summary>
+    /// Attempt to resolve an enum mapping.
+    /// </summary>
+    public bool TryGetLayer(Entity<SpriteComponent?> sprite, Enum key, [NotNullWhen(true)] out Layer? layer, bool logMissing)
+    {
+        layer = null;
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp, logMissing))
+            return false;
+
+        return LayerMapTryGet(sprite, key, out var index, logMissing)
+               && TryGetLayer(sprite, index, out layer, logMissing);
+    }
+
+    /// <summary>
+    /// Attempt to resolve a string mapping.
+    /// </summary>
+    public bool TryGetLayer(Entity<SpriteComponent?> sprite, string key, [NotNullWhen(true)] out Layer? layer, bool logMissing)
+    {
+        layer = null;
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp, logMissing))
+            return false;
+
+        return LayerMapTryGet(sprite, key, out var index, logMissing)
+               && TryGetLayer(sprite, index, out layer, logMissing);
+    }
+
+    public int LayerMapGet(Entity<SpriteComponent?> sprite, Enum key)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return -1;
+
+        return sprite.Comp.LayerMap[key];
+    }
+
+    public int LayerMapGet(Entity<SpriteComponent?> sprite, string key)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return -1;
+
+        return sprite.Comp.LayerMap[key];
+    }
+
+    public bool LayerExists(Entity<SpriteComponent?> sprite, string key)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return false;
+
+        return sprite.Comp.LayerMap.TryGetValue(key, out var index)
+               && LayerExists(sprite, index);
+    }
+
+    public bool LayerExists(Entity<SpriteComponent?> sprite, Enum key)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return false;
+
+        return sprite.Comp.LayerMap.TryGetValue(key, out var index)
+               && LayerExists(sprite, index);
+    }
+
+    /// <summary>
+    /// Ensures that a layer with the given key exists and return the layer's index.
+    /// If the layer does not yet exist, this will create and add a blank layer.
+    /// </summary>
+    public int LayerMapReserve(Entity<SpriteComponent?> sprite, Enum key)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return -1;
+
+        if (LayerMapTryGet(sprite, key, out var layerIndex, false))
+            return layerIndex;
+
+        var layer = AddBlankLayer(sprite!);
+        LayerMapSet(sprite, key, layer.Index);
+        return layer.Index;
+    }
+
+    /// <inheritdoc cref="LayerMapReserve(Entity{SpriteComponent?},System.Enum)"/>
+    public int LayerMapReserve(Entity<SpriteComponent?> sprite, string key)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return -1;
+
+        if (LayerMapTryGet(sprite, key, out var layerIndex, false))
+            return layerIndex;
+
+        var layer = AddBlankLayer(sprite!);
+        LayerMapSet(sprite, key, layer.Index);
+        return layer.Index;
+    }
+
+    public bool RemoveLayer(Entity<SpriteComponent?> sprite, string key, bool logMissing = true)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp, logMissing))
+            return false;
+
+        if (!LayerMapTryGet(sprite, key, out var index, logMissing))
+            return false;
+
+        return RemoveLayer(sprite, index, logMissing);
+    }
+
+    public bool RemoveLayer(Entity<SpriteComponent?> sprite, Enum key, bool logMissing = true)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp, logMissing))
+            return false;
+
+        if (!LayerMapTryGet(sprite, key, out var index, logMissing))
+            return false;
+
+        return RemoveLayer(sprite, index, logMissing);
+    }
+
+    public bool RemoveLayer(
+        Entity<SpriteComponent?> sprite,
+        string key,
+        [NotNullWhen(true)] out Layer? layer,
+        bool logMissing = true)
+    {
+        layer = null;
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp, logMissing))
+            return false;
+
+        if (!LayerMapTryGet(sprite, key, out var index, logMissing))
+            return false;
+
+        return RemoveLayer(sprite, index, out layer, logMissing);
+    }
+
+    public bool RemoveLayer(
+        Entity<SpriteComponent?> sprite,
+        Enum key,
+        [NotNullWhen(true)] out Layer? layer,
+        bool logMissing = true)
+    {
+        layer = null;
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp, logMissing))
+            return false;
+
+        if (!LayerMapTryGet(sprite, key, out var index, logMissing))
+            return false;
+
+        return RemoveLayer(sprite, index, out layer, logMissing);
+    }
+}

Robust.Client/GameObjects/EntitySystems/SpriteSystem.LayerSetters.cs

@@ -0,0 +1,605 @@
+using System;
+using System.Numerics;
+using Robust.Client.Graphics;
+using Robust.Client.ResourceManagement;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Maths;
+using Robust.Shared.Utility;
+using static Robust.Client.GameObjects.SpriteComponent;
+using static Robust.Client.Graphics.RSI;
+
+#pragma warning disable CS0618 // Type or member is obsolete
+
+namespace Robust.Client.GameObjects;
+
+// This partial class contains various public methods for modifying a layer's properties.
+public sealed partial class SpriteSystem
+{
+    #region SetData
+
+    public void LayerSetData(Entity<SpriteComponent?> sprite, int index, PrototypeLayerData data)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetData(layer, data);
+    }
+
+    public void LayerSetData(Entity<SpriteComponent?> sprite, string key, PrototypeLayerData data)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetData(layer, data);
+    }
+
+    public void LayerSetData(Entity<SpriteComponent?> sprite, Enum key, PrototypeLayerData data)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetData(layer, data);
+    }
+
+    public void LayerSetData(Layer layer, PrototypeLayerData data)
+    {
+        DebugTools.Assert(layer.Owner != default);
+        DebugTools.AssertNotNull(layer.Owner.Comp);
+        DebugTools.AssertEqual(layer.Owner.Comp.Layers[layer.Index], layer);
+        // TODO SPRITE ECS
+        layer._parent.LayerSetData(layer, data);
+    }
+
+    #endregion
+
+    #region SpriteSpecifier
+
+    public void LayerSetSprite(Entity<SpriteComponent?> sprite, int index, SpriteSpecifier specifier)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetSprite(layer, specifier);
+    }
+
+    public void LayerSetSprite(Entity<SpriteComponent?> sprite, string key, SpriteSpecifier specifier)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetSprite(layer, specifier);
+    }
+
+    public void LayerSetSprite(Entity<SpriteComponent?> sprite, Enum key, SpriteSpecifier specifier)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetSprite(layer, specifier);
+    }
+
+    public void LayerSetSprite(Layer layer, SpriteSpecifier specifier)
+    {
+        switch (specifier)
+        {
+            case SpriteSpecifier.Texture tex:
+                LayerSetTexture(layer, tex.TexturePath);
+                break;
+
+            case SpriteSpecifier.Rsi rsi:
+                LayerSetRsi(layer, rsi.RsiPath, rsi.RsiState);
+                break;
+
+            default:
+                throw new NotImplementedException();
+        }
+    }
+
+    #endregion
+
+    #region Texture
+
+    public void LayerSetTexture(Entity<SpriteComponent?> sprite, int index, Texture? texture)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetTexture(layer, texture);
+    }
+
+    public void LayerSetTexture(Entity<SpriteComponent?> sprite, string key, Texture? texture)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetTexture(layer, texture);
+    }
+
+    public void LayerSetTexture(Entity<SpriteComponent?> sprite, Enum key, Texture? texture)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetTexture(layer, texture);
+    }
+
+    public void LayerSetTexture(Layer layer, Texture? texture)
+    {
+        LayerSetRsiState(layer, StateId.Invalid, refresh: true);
+        layer.Texture = texture;
+    }
+
+    public void LayerSetTexture(Entity<SpriteComponent?> sprite, int index, ResPath path)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetTexture(layer, path);
+    }
+
+    public void LayerSetTexture(Entity<SpriteComponent?> sprite, string key, ResPath path)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetTexture(layer, path);
+    }
+
+    public void LayerSetTexture(Entity<SpriteComponent?> sprite, Enum key, ResPath path)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetTexture(layer, path);
+    }
+
+    private void LayerSetTexture(Layer layer, ResPath path)
+    {
+        if (!_resourceCache.TryGetResource<TextureResource>(TextureRoot / path, out var texture))
+        {
+            if (path.Extension == "rsi")
+                Log.Error($"Expected texture but got rsi '{path}', did you mean 'sprite:' instead of 'texture:'?");
+            Log.Error($"Unable to load texture '{path}'. Trace:\n{Environment.StackTrace}");
+        }
+
+        LayerSetTexture(layer, texture?.Texture);
+    }
+
+    #endregion
+
+    #region RsiState
+
+    public void LayerSetRsiState(Entity<SpriteComponent?> sprite, int index, StateId state)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetRsiState(layer, state);
+    }
+
+    public void LayerSetRsiState(Entity<SpriteComponent?> sprite, string key, StateId state)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetRsiState(layer, state);
+    }
+
+    public void LayerSetRsiState(Entity<SpriteComponent?> sprite, Enum key, StateId state)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetRsiState(layer, state);
+    }
+
+    public void LayerSetRsiState(Layer layer, StateId state, bool refresh = false)
+    {
+        DebugTools.Assert(layer.Owner != default);
+        DebugTools.AssertNotNull(layer.Owner.Comp);
+        DebugTools.AssertEqual(layer.Owner.Comp.Layers[layer.Index], layer);
+
+        if (layer.StateId == state && !refresh)
+            return;
+
+        layer.StateId = state;
+        RefreshCachedState(layer, true, null);
+        _tree.QueueTreeUpdate(layer.Owner);
+        QueueUpdateIsInert(layer.Owner);
+        layer.BoundsDirty = true;
+        layer.Owner.Comp.BoundsDirty = true;
+    }
+
+    #endregion
+
+    #region Rsi
+
+    public void LayerSetRsi(Entity<SpriteComponent?> sprite, int index, RSI? rsi, StateId? state = null)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetRsi(layer, rsi, state);
+    }
+
+    public void LayerSetRsi(Entity<SpriteComponent?> sprite, string key, RSI? rsi, StateId? state = null)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetRsi(layer, rsi, state);
+    }
+
+    public void LayerSetRsi(Entity<SpriteComponent?> sprite, Enum key, RSI? rsi, StateId? state = null)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetRsi(layer, rsi, state);
+    }
+
+    public void LayerSetRsi(Layer layer, RSI? rsi, StateId? state = null)
+    {
+        layer._rsi = rsi;
+        LayerSetRsiState(layer, state ?? layer.StateId, refresh: true);
+    }
+
+    public void LayerSetRsi(Entity<SpriteComponent?> sprite, int index, ResPath rsi, StateId? state = null)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetRsi(layer, rsi, state);
+    }
+
+    public void LayerSetRsi(Entity<SpriteComponent?> sprite, string key, ResPath rsi, StateId? state = null)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetRsi(layer, rsi, state);
+    }
+
+    public void LayerSetRsi(Entity<SpriteComponent?> sprite, Enum key, ResPath rsi, StateId? state = null)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetRsi(layer, rsi, state);
+    }
+
+    public void LayerSetRsi(Layer layer, ResPath rsi, StateId? state = null)
+    {
+        if (!_resourceCache.TryGetResource<RSIResource>(TextureRoot / rsi, out var res))
+            Log.Error($"Unable to load RSI '{rsi}' for entity {ToPrettyString(layer.Owner)}. Trace:\n{Environment.StackTrace}");
+
+        LayerSetRsi(layer, res?.RSI, state);
+    }
+
+    #endregion
+
+    #region Scale
+
+    public void LayerSetScale(Entity<SpriteComponent?> sprite, int index, Vector2 value)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetScale(layer, value);
+    }
+
+    public void LayerSetScale(Entity<SpriteComponent?> sprite, string key, Vector2 value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetScale(layer, value);
+    }
+
+    public void LayerSetScale(Entity<SpriteComponent?> sprite, Enum key, Vector2 value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetScale(layer, value);
+    }
+
+    public void LayerSetScale(Layer layer, Vector2 value)
+    {
+        DebugTools.Assert(layer.Owner != default);
+        DebugTools.AssertNotNull(layer.Owner.Comp);
+        DebugTools.AssertEqual(layer.Owner.Comp.Layers[layer.Index], layer);
+
+        if (layer._scale.EqualsApprox(value))
+            return;
+
+        if (!ValidateScale(layer.Owner, value))
+            return;
+
+        layer._scale = value;
+        layer.UpdateLocalMatrix();
+        _tree.QueueTreeUpdate(layer.Owner);
+        layer.BoundsDirty = true;
+        layer.Owner.Comp.BoundsDirty = true;
+    }
+
+    #endregion
+
+    #region Rotation
+
+    public void LayerSetRotation(Entity<SpriteComponent?> sprite, int index, Angle value)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetRotation(layer, value);
+    }
+
+    public void LayerSetRotation(Entity<SpriteComponent?> sprite, string key, Angle value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetRotation(layer, value);
+    }
+
+    public void LayerSetRotation(Entity<SpriteComponent?> sprite, Enum key, Angle value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetRotation(layer, value);
+    }
+
+    public void LayerSetRotation(Layer layer, Angle value)
+    {
+        DebugTools.Assert(layer.Owner != default);
+        DebugTools.AssertNotNull(layer.Owner.Comp);
+        DebugTools.AssertEqual(layer.Owner.Comp.Layers[layer.Index], layer);
+
+        if (layer._rotation.EqualsApprox(value))
+            return;
+
+        layer._rotation = value;
+        layer.UpdateLocalMatrix();
+        _tree.QueueTreeUpdate(layer.Owner);
+        layer.BoundsDirty = true;
+        layer.Owner.Comp.BoundsDirty = true;
+    }
+
+    #endregion
+
+    #region Offset
+
+    public void LayerSetOffset(Entity<SpriteComponent?> sprite, int index, Vector2 value)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetOffset(layer, value);
+    }
+
+    public void LayerSetOffset(Entity<SpriteComponent?> sprite, string key, Vector2 value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetOffset(layer, value);
+    }
+
+    public void LayerSetOffset(Entity<SpriteComponent?> sprite, Enum key, Vector2 value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetOffset(layer, value);
+    }
+
+    public void LayerSetOffset(Layer layer, Vector2 value)
+    {
+        DebugTools.Assert(layer.Owner != default);
+        DebugTools.AssertNotNull(layer.Owner.Comp);
+        DebugTools.AssertEqual(layer.Owner.Comp.Layers[layer.Index], layer);
+
+        if (layer._offset.EqualsApprox(value))
+            return;
+
+        layer._offset = value;
+        layer.UpdateLocalMatrix();
+        _tree.QueueTreeUpdate(layer.Owner);
+        layer.BoundsDirty = true;
+        layer.Owner.Comp.BoundsDirty = true;
+    }
+
+    #endregion
+
+    #region Visible
+
+    public void LayerSetVisible(Entity<SpriteComponent?> sprite, int index, bool value)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetVisible(layer, value);
+    }
+
+    public void LayerSetVisible(Entity<SpriteComponent?> sprite, string key, bool value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetVisible(layer, value);
+    }
+
+    public void LayerSetVisible(Entity<SpriteComponent?> sprite, Enum key, bool value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetVisible(layer, value);
+    }
+
+    public void LayerSetVisible(Layer layer, bool value)
+    {
+        DebugTools.Assert(layer.Owner != default);
+        DebugTools.AssertNotNull(layer.Owner.Comp);
+        DebugTools.AssertEqual(layer.Owner.Comp.Layers[layer.Index], layer);
+
+        if (layer._visible == value)
+            return;
+
+        layer._visible = value;
+        QueueUpdateIsInert(layer.Owner);
+        _tree.QueueTreeUpdate(layer.Owner);
+        layer.Owner.Comp.BoundsDirty = true;
+    }
+
+    #endregion
+
+    #region Color
+
+    public void LayerSetColor(Entity<SpriteComponent?> sprite, int index, Color value)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetColor(layer, value);
+    }
+
+    public void LayerSetColor(Entity<SpriteComponent?> sprite, string key, Color value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetColor(layer, value);
+    }
+
+    public void LayerSetColor(Entity<SpriteComponent?> sprite, Enum key, Color value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetColor(layer, value);
+    }
+
+    public void LayerSetColor(Layer layer, Color value)
+    {
+        DebugTools.Assert(layer.Owner != default);
+        DebugTools.AssertNotNull(layer.Owner.Comp);
+        DebugTools.AssertEqual(layer.Owner.Comp.Layers[layer.Index], layer);
+
+        layer.Color = value;
+    }
+
+    #endregion
+
+    #region DirOffset
+
+    public void LayerSetDirOffset(Entity<SpriteComponent?> sprite, int index, DirectionOffset value)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetDirOffset(layer, value);
+    }
+
+    public void LayerSetDirOffset(Entity<SpriteComponent?> sprite, string key, DirectionOffset value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetDirOffset(layer, value);
+    }
+
+    public void LayerSetDirOffset(Entity<SpriteComponent?> sprite, Enum key, DirectionOffset value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetDirOffset(layer, value);
+    }
+
+    public void LayerSetDirOffset(Layer layer, DirectionOffset value)
+    {
+        DebugTools.Assert(layer.Owner != default);
+        DebugTools.AssertNotNull(layer.Owner.Comp);
+        DebugTools.AssertEqual(layer.Owner.Comp.Layers[layer.Index], layer);
+
+        layer.DirOffset = value;
+    }
+
+    #endregion
+
+    #region AnimationTime
+
+    public void LayerSetAnimationTime(Entity<SpriteComponent?> sprite, int index, float value)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetAnimationTime(layer, value);
+    }
+
+    public void LayerSetAnimationTime(Entity<SpriteComponent?> sprite, string key, float value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetAnimationTime(layer, value);
+    }
+
+    public void LayerSetAnimationTime(Entity<SpriteComponent?> sprite, Enum key, float value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetAnimationTime(layer, value);
+    }
+
+    public void LayerSetAnimationTime(Layer layer, float value)
+    {
+        DebugTools.Assert(layer.Owner != default);
+        DebugTools.AssertNotNull(layer.Owner.Comp);
+        DebugTools.AssertEqual(layer.Owner.Comp.Layers[layer.Index], layer);
+
+        if (!layer.StateId.IsValid)
+            return;
+
+        if (layer.ActualRsi is not { } rsi)
+            return;
+
+        var state = rsi[layer.StateId];
+        if (value > layer.AnimationTime)
+        {
+            // Handle advancing differently from going backwards.
+            layer.AnimationTimeLeft -= (value - layer.AnimationTime);
+        }
+        else
+        {
+            // Going backwards we re-calculate from zero.
+            // Definitely possible to optimize this for going backwards but I'm too lazy to figure that out.
+            layer.AnimationTimeLeft = -value + state.GetDelay(0);
+            layer.AnimationFrame = 0;
+        }
+
+        layer.AnimationTime = value;
+        layer.AdvanceFrameAnimation(state);
+        layer.SetAnimationTime(value);
+    }
+
+    #endregion
+
+    #region AutoAnimated
+
+    public void LayerSetAutoAnimated(Entity<SpriteComponent?> sprite, int index, bool value)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetAutoAnimated(layer, value);
+    }
+
+    public void LayerSetAutoAnimated(Entity<SpriteComponent?> sprite, string key, bool value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetAutoAnimated(layer, value);
+    }
+
+    public void LayerSetAutoAnimated(Entity<SpriteComponent?> sprite, Enum key, bool value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetAutoAnimated(layer, value);
+    }
+
+    public void LayerSetAutoAnimated(Layer layer, bool value)
+    {
+        DebugTools.Assert(layer.Owner != default);
+        DebugTools.AssertNotNull(layer.Owner.Comp);
+        DebugTools.AssertEqual(layer.Owner.Comp.Layers[layer.Index], layer);
+
+        if (layer._autoAnimated == value)
+            return;
+
+        layer._autoAnimated = value;
+        QueueUpdateIsInert(layer.Owner);
+    }
+
+    #endregion
+
+    #region LayerSetRenderingStrategy
+
+    public void LayerSetRenderingStrategy(Entity<SpriteComponent?> sprite, int index, LayerRenderingStrategy value)
+    {
+        if (TryGetLayer(sprite, index, out var layer, true))
+            LayerSetRenderingStrategy(layer, value);
+    }
+
+    public void LayerSetRenderingStrategy(Entity<SpriteComponent?> sprite, string key, LayerRenderingStrategy value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetRenderingStrategy(layer, value);
+    }
+
+    public void LayerSetRenderingStrategy(Entity<SpriteComponent?> sprite, Enum key, LayerRenderingStrategy value)
+    {
+        if (TryGetLayer(sprite, key, out var layer, true))
+            LayerSetRenderingStrategy(layer, value);
+    }
+
+    public void LayerSetRenderingStrategy(Layer layer, LayerRenderingStrategy value)
+    {
+        DebugTools.Assert(layer.Owner != default);
+        DebugTools.AssertNotNull(layer.Owner.Comp);
+        DebugTools.AssertEqual(layer.Owner.Comp.Layers[layer.Index], layer);
+
+        layer.RenderingStrategy = value;
+        layer.BoundsDirty = true;
+        layer.Owner.Comp.BoundsDirty = true;
+        _tree.QueueTreeUpdate(layer.Owner);
+    }
+
+    #endregion
+
+    /// <summary>
+    /// Refreshes an RSI layer's cached RSI state.
+    /// </summary>
+    private void RefreshCachedState(Layer layer, bool logErrors, RSI.State? fallback)
+    {
+        if (!layer.StateId.IsValid)
+        {
+            layer._actualState = null;
+        }
+        else if (layer.ActualRsi is not { } rsi)
+        {
+            layer._actualState = fallback ?? GetFallbackState();
+            if (logErrors)
+                Log.Error(
+                    $"{ToPrettyString(layer.Owner)} has no RSI to pull new state from! Trace:\n{Environment.StackTrace}");
+        }
+        else if (!rsi.TryGetState(layer.StateId, out layer._actualState))
+        {
+            layer._actualState = fallback ?? GetFallbackState();
+            if (logErrors)
+                Log.Error(
+                    $"{ToPrettyString(layer.Owner)}'s state '{layer.StateId}' does not exist in RSI {rsi.Path}. Trace:\n{Environment.StackTrace}");
+        }
+
+        layer.AnimationFrame = 0;
+        layer.AnimationTime = 0;
+        layer.AnimationTimeLeft = layer._actualState?.GetDelay(0) ?? 0f;
+    }
+}

Robust.Client/GameObjects/EntitySystems/SpriteSystem.Render.cs

@@ -0,0 +1,196 @@
+using System.Numerics;
+using Robust.Client.Graphics;
+using Robust.Client.Graphics.Clyde;
+using Robust.Client.Utility;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Graphics.RSI;
+using Robust.Shared.Maths;
+using Robust.Shared.Utility;
+using static Robust.Client.GameObjects.SpriteComponent;
+using Vector4 = Robust.Shared.Maths.Vector4;
+using SysVec4 = System.Numerics.Vector4;
+
+namespace Robust.Client.GameObjects;
+
+// This partial class contains code related to actually rendering sprites.
+public sealed partial class SpriteSystem
+{
+    public void RenderSprite(
+        Entity<SpriteComponent> sprite,
+        DrawingHandleWorld drawingHandle,
+        Angle eyeRotation,
+        Angle worldRotation,
+        Vector2 worldPosition)
+    {
+        RenderSprite(sprite,
+            drawingHandle,
+            eyeRotation,
+            worldRotation,
+            worldPosition,
+            sprite.Comp.EnableDirectionOverride ? sprite.Comp.DirectionOverride : null);
+    }
+
+    public void RenderSprite(
+        Entity<SpriteComponent> sprite,
+        DrawingHandleWorld drawingHandle,
+        Angle eyeRotation,
+        Angle worldRotation,
+        Vector2 worldPosition,
+        Direction? overrideDirection)
+    {
+        // TODO SPRITE RENDERING
+        // Add fast path for simple sprites.
+        // I.e., when a sprite is modified, check if it is "simple". If it is. cache texture information in a struct
+        // and use a fast path here.
+        // E.g., simple 1-directional, 1-layer sprites can basically become a direct texture draw call. (most in game items).
+        // Similarly, 1-directional multi-layer sprites can become a sequence of direct draw calls (most in game walls).
+
+        if (!sprite.Comp.IsInert)
+            _queuedFrameUpdate.Add(sprite);
+
+        var angle = worldRotation + eyeRotation; // angle on-screen. Used to decide the direction of 4/8 directional RSIs
+        angle = angle.Reduced().FlipPositive();  // Reduce the angles to fix math shenanigans
+
+        var cardinal = Angle.Zero;
+
+        // If we have a 1-directional sprite then snap it to try and always face it south if applicable.
+        if (sprite.Comp is {NoRotation: false, SnapCardinals: true})
+            cardinal = angle.RoundToCardinalAngle();
+
+        // worldRotation + eyeRotation should be the angle of the entity on-screen. If no-rot is enabled this is just set to zero.
+        // However, at some point later the eye-matrix is applied separately, so we subtract -eye rotation for now:
+        var entityMatrix = Matrix3Helpers.CreateTransform(worldPosition, sprite.Comp.NoRotation ? -eyeRotation : worldRotation - cardinal);
+        var spriteMatrix = Matrix3x2.Multiply(sprite.Comp.LocalMatrix, entityMatrix);
+
+        // Fast path for when all sprites use the same transform matrix
+        if (!sprite.Comp.GranularLayersRendering)
+        {
+            foreach (var layer in sprite.Comp.Layers)
+            {
+                RenderLayer(layer, drawingHandle, ref spriteMatrix, angle, overrideDirection);
+            }
+            return;
+        }
+
+        //Default rendering (NoRotation = false)
+        entityMatrix = Matrix3Helpers.CreateTransform(worldPosition, worldRotation);
+        var transformDefault = Matrix3x2.Multiply(sprite.Comp.LocalMatrix, entityMatrix);
+
+        //Snap to cardinals
+        entityMatrix = Matrix3Helpers.CreateTransform(worldPosition, worldRotation - angle.RoundToCardinalAngle());
+        var transformSnap = Matrix3x2.Multiply(sprite.Comp.LocalMatrix, entityMatrix);
+
+        //No rotation
+        entityMatrix = Matrix3Helpers.CreateTransform(worldPosition, -eyeRotation);
+        var transformNoRot = Matrix3x2.Multiply(sprite.Comp.LocalMatrix, entityMatrix);
+
+        foreach (var layer in sprite.Comp.Layers)
+        {
+            switch (layer.RenderingStrategy)
+            {
+                case LayerRenderingStrategy.UseSpriteStrategy:
+                    RenderLayer(layer, drawingHandle, ref spriteMatrix, angle, overrideDirection);
+                    break;
+                case LayerRenderingStrategy.Default:
+                    RenderLayer(layer, drawingHandle, ref transformDefault, angle, overrideDirection);
+                    break;
+                case LayerRenderingStrategy.NoRotation:
+                    RenderLayer(layer, drawingHandle, ref transformNoRot, angle, overrideDirection);
+                    break;
+                case LayerRenderingStrategy.SnapToCardinals:
+                    RenderLayer(layer, drawingHandle, ref transformSnap, angle, overrideDirection);
+                    break;
+                default:
+                    Log.Error($"Tried to render a layer with unknown rendering stragegy: {layer.RenderingStrategy}");
+                    break;
+            }
+        }
+    }
+
+    /// <summary>
+    /// Render a layer. This assumes that the input angle is between 0 and 2pi.
+    /// </summary>
+    private void RenderLayer(Layer layer, DrawingHandleWorld drawingHandle, ref Matrix3x2 spriteMatrix, Angle angle, Direction? overrideDirection)
+    {
+        if (!layer.Visible || layer.Blank)
+            return;
+
+        var state = layer._actualState;
+        var dir = state == null ? RsiDirection.South : Layer.GetDirection(state.RsiDirections, angle);
+
+        // Set the drawing transform for this layer
+        layer.GetLayerDrawMatrix(dir, out var layerMatrix, layer.Owner.Comp.NoRotation);
+
+        // The direction used to draw the sprite can differ from the one that the angle would naively suggest,
+        // due to direction overrides or offsets.
+        if (overrideDirection != null && state != null)
+            dir = overrideDirection.Value.Convert(state.RsiDirections);
+        dir = dir.OffsetRsiDir(layer.DirOffset);
+
+        var texture = state?.GetFrame(dir, layer.AnimationFrame) ?? layer.Texture ?? GetFallbackTexture();
+
+        // TODO SPRITE
+        // Refactor shader-param-layers to a separate layer type after layers are split into types & collections.
+        // I.e., separate Layer -> RsiLayer, TextureLayer, LayerCollection, SpriteLayer, and ShaderLayer
+        if (layer.CopyToShaderParameters != null)
+        {
+            HandleShaderLayer(layer, texture, layer.CopyToShaderParameters);
+            return;
+        }
+
+        // Set the drawing transform for this layer
+        var transformMatrix = Matrix3x2.Multiply(layerMatrix, spriteMatrix);
+        drawingHandle.SetTransform(in transformMatrix);
+
+        if (layer.Shader != null)
+            drawingHandle.UseShader(layer.Shader);
+
+        var layerColor = layer.Owner.Comp.color * layer.Color;
+        var textureSize = texture.Size / (float) EyeManager.PixelsPerMeter;
+        var quad = Box2.FromDimensions(textureSize / -2, textureSize);
+
+        if (layer.UnShaded)
+        {
+            DebugTools.AssertNull(layer.Shader);
+            DebugTools.Assert(layerColor is {R: >= 0, G: >= 0, B: >= 0, A: >= 0}, "Default shader should not be used with negative color modulation.");
+
+            // Negative color modulation values are by the default shader to disable light shading.
+            // Specifically we set colour = - 1 - colour
+            // This is good enough to ensure that non-negative values become negative & is trivially invertible.
+            layerColor = new(new SysVec4(-1) - layerColor.RGBA);
+        }
+
+        drawingHandle.DrawTextureRectRegion(texture, quad, layerColor);
+
+        if (layer.Shader != null)
+            drawingHandle.UseShader(null);
+    }
+
+    /// <summary>
+    /// Handle a a "fake layer" that just exists to modify the parameters of a shader being used by some other
+    /// layer.
+    /// </summary>
+    private void HandleShaderLayer(Layer layer, Texture texture, CopyToShaderParameters @params)
+    {
+        // Multiple atrocities to god being committed right here.
+        var otherLayerIdx = layer._parent.LayerMap[@params.LayerKey!];
+        var otherLayer = layer._parent.Layers[otherLayerIdx];
+        if (otherLayer.Shader is not { } shader)
+            return;
+
+        if (!shader.Mutable)
+            otherLayer.Shader = shader = shader.Duplicate();
+
+        var clydeTexture = Clyde.RenderHandle.ExtractTexture(texture, null, out var csr);
+
+        if (@params.ParameterTexture is { } paramTexture)
+            shader.SetParameter(paramTexture, clydeTexture);
+
+        if (@params.ParameterUV is not { } paramUV)
+            return;
+
+        var sr = Clyde.RenderHandle.WorldTextureBoundsToUV(clydeTexture, csr);
+        var uv = new Vector4(sr.Left, sr.Bottom, sr.Right, sr.Top);
+        shader.SetParameter(paramUV, uv);
+    }
+}

Robust.Client/GameObjects/EntitySystems/SpriteSystem.Setters.cs

@@ -0,0 +1,166 @@
+using System;
+using System.Numerics;
+using Robust.Client.Graphics;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Maths;
+
+namespace Robust.Client.GameObjects;
+
+// This partial class contains various public methods for setting sprite component data.
+public sealed partial class SpriteSystem
+{
+    private bool ValidateScale(Entity<SpriteComponent> sprite, Vector2 scale)
+    {
+        if (!(MathF.Abs(scale.X) < 0.005f) && !(MathF.Abs(scale.Y) < 0.005f))
+            return true;
+
+        // Scales of ~0.0025 or lower can lead to singular matrices due to rounding errors.
+        Log.Error(
+            $"Attempted to set layer sprite scale to very small values. Entity: {ToPrettyString(sprite)}. Scale: {scale}");
+
+        return false;
+    }
+
+    #region Transform
+    public void SetScale(Entity<SpriteComponent?> sprite, Vector2 value)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return;
+
+        if (!ValidateScale(sprite!, value))
+            return;
+
+        sprite.Comp._bounds = sprite.Comp._bounds.Scale(value / sprite.Comp.scale);
+        sprite.Comp.scale = value;
+        sprite.Comp.LocalMatrix = Matrix3Helpers.CreateTransform(
+            in sprite.Comp.offset,
+            in sprite.Comp.rotation,
+            in sprite.Comp.scale);
+    }
+
+    public void SetRotation(Entity<SpriteComponent?> sprite, Angle value)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return;
+
+        sprite.Comp.rotation = value;
+        sprite.Comp.LocalMatrix = Matrix3Helpers.CreateTransform(
+            in sprite.Comp.offset,
+            in sprite.Comp.rotation,
+            in sprite.Comp.scale);
+    }
+
+    public void SetOffset(Entity<SpriteComponent?> sprite, Vector2 value)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return;
+
+        sprite.Comp.offset = value;
+        sprite.Comp.LocalMatrix = Matrix3Helpers.CreateTransform(
+            in sprite.Comp.offset,
+            in sprite.Comp.rotation,
+            in sprite.Comp.scale);
+    }
+    #endregion
+
+    public void SetVisible(Entity<SpriteComponent?> sprite, bool value)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return;
+
+        if (sprite.Comp.Visible == value)
+            return;
+
+        sprite.Comp._visible = value;
+        _tree.QueueTreeUpdate(sprite!);
+    }
+
+    public void SetDrawDepth(Entity<SpriteComponent?> sprite, int value)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return;
+
+        sprite.Comp.drawDepth = value;
+    }
+
+    public void SetColor(Entity<SpriteComponent?> sprite, Color value)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return;
+
+        sprite.Comp.color = value;
+    }
+
+    /// <summary>
+    /// Modify a sprites base RSI. This is the RSI that is used by any RSI layers that do not specify their own.
+    /// Note that changing the base RSI may result in existing layers having an invalid state. This will not log errors
+    /// under the assumption that the states of each layers will be updated after the base RSI has changed.
+    /// </summary>
+    public void SetBaseRsi(Entity<SpriteComponent?> sprite, RSI? value)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return;
+
+        if (value == sprite.Comp._baseRsi)
+            return;
+
+        sprite.Comp._baseRsi = value;
+        if (value == null)
+            return;
+
+        var fallback = GetFallbackState();
+        for (var i = 0; i < sprite.Comp.Layers.Count; i++)
+        {
+            var layer = sprite.Comp.Layers[i];
+            if (!layer.State.IsValid || layer.RSI != null)
+                continue;
+
+            RefreshCachedState(layer, logErrors: false, fallback);
+
+            if (value.TryGetState(layer.State, out var state))
+            {
+                layer.AnimationTimeLeft = state.GetDelay(0);
+            }
+            else
+            {
+                Log.Error($"Layer {i} no longer has state '{layer.State}' due to base RSI change. Trace:\n{Environment.StackTrace}");
+                layer.Texture = null;
+            }
+        }
+    }
+
+    public void SetContainerOccluded(Entity<SpriteComponent?> sprite, bool value)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return;
+
+        sprite.Comp._containerOccluded = value;
+        _tree.QueueTreeUpdate(sprite!);
+    }
+
+    public void SetSnapCardinals(Entity<SpriteComponent?> sprite, bool value)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return;
+
+        if (value == sprite.Comp._snapCardinals)
+            return;
+
+        sprite.Comp._snapCardinals = value;
+        _tree.QueueTreeUpdate(sprite!);
+        DirtyBounds(sprite!);
+    }
+
+    public void SetGranularLayersRendering(Entity<SpriteComponent?> sprite, bool value)
+    {
+        if (!_query.Resolve(sprite.Owner, ref sprite.Comp))
+            return;
+
+        if (value == sprite.Comp.GranularLayersRendering)
+            return;
+
+        sprite.Comp.GranularLayersRendering = value;
+        _tree.QueueTreeUpdate(sprite!);
+        DirtyBounds(sprite!);
+    }
+}

Robust.Client/GameObjects/EntitySystems/SpriteSystem.Specifier.cs

@@ -1,137 +0,0 @@
-using System;
-using System.Collections.Generic;
-using JetBrains.Annotations;
-using Robust.Client.Graphics;
-using Robust.Client.ResourceManagement;
-using Robust.Client.Utility;
-using Robust.Shared.Graphics;
-using Robust.Shared.Map;
-using Robust.Shared.Prototypes;
-using Robust.Shared.Serialization.TypeSerializers.Implementations;
-using Robust.Shared.Utility;
-
-namespace Robust.Client.GameObjects;
-
-public sealed partial class SpriteSystem
-{
-    private readonly Dictionary<string, IRsiStateLike> _cachedPrototypeIcons = new();
-
-    public Texture Frame0(EntityPrototype prototype)
-    {
-        return GetPrototypeIcon(prototype).Default;
-    }
-
-    public Texture Frame0(SpriteSpecifier specifier)
-    {
-        return RsiStateLike(specifier).Default;
-    }
-
-    public IRsiStateLike RsiStateLike(SpriteSpecifier specifier)
-    {
-        switch (specifier)
-        {
-            case SpriteSpecifier.Texture tex:
-                return tex.GetTexture(_resourceCache);
-
-            case SpriteSpecifier.Rsi rsi:
-                return GetState(rsi);
-
-            case SpriteSpecifier.EntityPrototype prototypeIcon:
-                return GetPrototypeIcon(prototypeIcon.EntityPrototypeId);
-
-            default:
-                throw new NotSupportedException();
-        }
-    }
-
-    public Texture GetIcon(IconComponent icon)
-    {
-        return GetState(icon.Icon).Frame0;
-    }
-
-    /// <summary>
-    ///     Returns an icon for a given <see cref="EntityPrototype"/> ID, or a fallback in case of an error.
-    ///     This method caches the result based on the prototype identifier.
-    /// </summary>
-    public IRsiStateLike GetPrototypeIcon(string prototype)
-    {
-        // Check if this prototype has been cached before, and if so return the result.
-        if (_cachedPrototypeIcons.TryGetValue(prototype, out var cachedResult))
-            return cachedResult;
-
-        if (!_proto.TryIndex<EntityPrototype>(prototype, out var entityPrototype))
-        {
-            // The specified prototype doesn't exist, return the fallback "error" sprite.
-            _sawmill.Error("Failed to load PrototypeIcon {0}", prototype);
-            return GetFallbackState();
-        }
-
-        // Generate the icon and cache it in case it's ever needed again.
-        var result = GetPrototypeIcon(entityPrototype);
-        _cachedPrototypeIcons[prototype] = result;
-
-        return result;
-    }
-
-    /// <summary>
-    ///     Returns an icon for a given <see cref="EntityPrototype"/> ID, or a fallback in case of an error.
-    ///     This method does NOT cache the result.
-    /// </summary>
-    public IRsiStateLike GetPrototypeIcon(EntityPrototype prototype)
-    {
-        // IconComponent takes precedence. If it has a valid icon, return that. Otherwise, continue as normal.
-        if (prototype.Components.TryGetValue("Icon", out var compData)
-            && compData.Component is IconComponent icon)
-        {
-            return GetIcon(icon);
-        }
-
-        // If the prototype doesn't have a SpriteComponent, then there's nothing we can do but return the fallback.
-        if (!prototype.Components.ContainsKey("Sprite"))
-        {
-            return GetFallbackState();
-        }
-
-        // Finally, we use spawn a dummy entity to get its icon.
-        var dummy = Spawn(prototype.ID, MapCoordinates.Nullspace);
-        var spriteComponent = EnsureComp<SpriteComponent>(dummy);
-        var result = spriteComponent.Icon ?? GetFallbackState();
-        Del(dummy);
-
-        return result;
-    }
-
-    [Pure]
-    public RSI.State GetFallbackState()
-    {
-        return _resourceCache.GetFallback<RSIResource>().RSI["error"];
-    }
-
-    [Pure]
-    public RSI.State GetState(SpriteSpecifier.Rsi rsiSpecifier)
-    {
-        if (_resourceCache.TryGetResource<RSIResource>(
-                SpriteSpecifierSerializer.TextureRoot / rsiSpecifier.RsiPath,
-                out var theRsi) &&
-            theRsi.RSI.TryGetState(rsiSpecifier.RsiState, out var state))
-        {
-            return state;
-        }
-
-        _sawmill.Error("Failed to load RSI {0}", rsiSpecifier.RsiPath);
-        return GetFallbackState();
-    }
-
-    private void OnPrototypesReloaded(PrototypesReloadedEventArgs args)
-    {
-        if (!args.TryGetModified<EntityPrototype>(out var modified))
-            return;
-
-        // Remove all changed prototypes from the cache, if they're there.
-        foreach (var prototype in modified)
-        {
-            // Let's be lazy and not regenerate them until something needs them again.
-            _cachedPrototypeIcons.Remove(prototype);
-        }
-    }
-}

Robust.Client/GameObjects/EntitySystems/SpriteSystem.cs

@@ -13,10 +13,9 @@ using Robust.Shared.GameObjects;
 using Robust.Shared.Graphics.RSI;
 using Robust.Shared.IoC;
 using Robust.Shared.Log;
-using Robust.Shared.Map;
 using Robust.Shared.Maths;
-using Robust.Shared.Physics;
 using Robust.Shared.Prototypes;
+using Robust.Shared.Serialization.TypeSerializers.Implementations;
 using Robust.Shared.Timing;
 using Robust.Shared.Utility;
 using static Robust.Client.GameObjects.SpriteComponent;
@@ -36,24 +35,20 @@ namespace Robust.Client.GameObjects
         [Dependency] private readonly IResourceCache _resourceCache = default!;
         [Dependency] private readonly ILogManager _logManager = default!;
         [Dependency] private readonly SharedTransformSystem _xforms = default!;
+        [Dependency] private readonly SpriteTreeSystem _tree = default!;
 
         public static readonly ProtoId<ShaderPrototype> UnshadedId = "unshaded";
         private readonly Queue<SpriteComponent> _inertUpdateQueue = new();
 
+        public static readonly ResPath TextureRoot = SpriteSpecifierSerializer.TextureRoot;
+
         /// <summary>
         ///     Entities that require a sprite frame update.
         /// </summary>
         private readonly HashSet<EntityUid> _queuedFrameUpdate = new();
 
         private ISawmill _sawmill = default!;
-
-        internal void Render(EntityUid uid, SpriteComponent sprite, DrawingHandleWorld drawingHandle, Angle eyeRotation, in Angle worldRotation, in Vector2 worldPosition)
-        {
-            if (!sprite.IsInert)
-                _queuedFrameUpdate.Add(uid);
-
-            sprite.RenderInternal(drawingHandle, eyeRotation, worldRotation, worldPosition, sprite.EnableDirectionOverride ? sprite.DirectionOverride : null);
-        }
+        private EntityQuery<SpriteComponent> _query;
 
         public override void Initialize()
         {
@@ -62,11 +57,11 @@ namespace Robust.Client.GameObjects
             UpdatesAfter.Add(typeof(SpriteTreeSystem));
 
             SubscribeLocalEvent<PrototypesReloadedEventArgs>(OnPrototypesReloaded);
-            SubscribeLocalEvent<SpriteComponent, SpriteUpdateInertEvent>(QueueUpdateInert);
             SubscribeLocalEvent<SpriteComponent, ComponentInit>(OnInit);
 
             Subs.CVar(_cfg, CVars.RenderSpriteDirectionBias, OnBiasChanged, true);
             _sawmill = _logManager.GetSawmill("sprite");
+            _query = GetEntityQuery<SpriteComponent>();
         }
 
         public bool IsVisible(Layer layer)
@@ -85,18 +80,6 @@ namespace Robust.Client.GameObjects
             SpriteComponent.DirectionBias = value;
         }
 
-        private void QueueUpdateInert(EntityUid uid, SpriteComponent sprite, ref SpriteUpdateInertEvent ev)
-            => QueueUpdateInert(uid, sprite);
-
-        public void QueueUpdateInert(EntityUid uid, SpriteComponent sprite)
-        {
-            if (sprite._inertUpdateQueued)
-                return;
-
-            sprite._inertUpdateQueued = true;
-            _inertUpdateQueue.Enqueue(sprite);
-        }
-
         private void DoUpdateIsInert(SpriteComponent component)
         {
             component._inertUpdateQueued = false;

Robust.Client/GameObjects/EntitySystems/VisualizerSystem.cs

@@ -11,6 +11,7 @@ public abstract class VisualizerSystem<T> : EntitySystem
 {
     [Dependency] protected readonly AppearanceSystem AppearanceSystem = default!;
     [Dependency] protected readonly AnimationPlayerSystem AnimationSystem = default!;
+    [Dependency] protected readonly SpriteSystem SpriteSystem = default!;
 
     public override void Initialize()
     {

Robust.Client/GameStates/ClientGameStateManager.cs

@@ -1306,6 +1306,11 @@ namespace Robust.Client.GameStates
                     meta.LastStateApplied = lastStateApplied.Value;
 
                 var xform = xforms.GetComponent(ent.Value);
+
+                // TODO PVS DETACH
+                // Why is this if block here again? If a null-space entity gets sent to a player via some PVS override,
+                // and then later on it gets removed, you would assume that the client marks it as detached?
+                // I.e., modifying the metadata flag & pausing the entity should probably happen outside of this block.
                 if (xform.ParentUid.IsValid())
                 {
                     lookupSys.RemoveFromEntityTree(ent.Value, xform);
@@ -1326,6 +1331,13 @@ namespace Robust.Client.GameStates
                     xformSys.DetachEntity(ent.Value, xform);
                     DebugTools.Assert((meta.Flags & MetaDataFlags.InContainer) == 0);
 
+                    // We mark the entity as paused, without raising a pause-event.
+                    // The entity gets un-paused when the metadata's comp-state is reapplied (which also does not raise
+                    // an un-pause event). The assumption is that game logic that has to handle the pausing should be
+                    // getting networked anyway. And if its some client-side timer on a networked entity, the timer
+                    // shouldn't actually be getting paused just because the entity has left the players view.
+                    meta.PauseTime = TimeSpan.Zero;
+
                     if (container != null)
                         containerSys.AddExpectedEntity(netEntity, container);
                 }

Robust.Client/Graphics/Clyde/Clyde.GridRendering.cs

@@ -254,7 +254,11 @@ namespace Robust.Client.Graphics.Clyde
                             region = regionMaybe[tile.Variant];
                         }
 
-                        WriteTileToBuffers(i, gridX, gridY, vertexBuffer, indexBuffer, region);
+                        var rotationMirroring = _tileDefinitionManager[tile.TypeId].AllowRotationMirror
+                            ? tile.RotationMirroring
+                            : 0;
+
+                        WriteTileToBuffers(i, gridX, gridY, vertexBuffer, indexBuffer, region, rotationMirroring);
                         i += 1;
                     }
                 }
@@ -325,7 +329,7 @@ namespace Robust.Client.Graphics.Clyde
                                 continue;
 
                             var region = regionMaybe[0];
-                            WriteTileToBuffers(i, gridX, gridY, vertexBuffer, indexBuffer, region);
+                            WriteTileToBuffers(i, gridX, gridY, vertexBuffer, indexBuffer, region, 0);
                             i += 1;
                         }
                     }
@@ -408,8 +412,11 @@ namespace Robust.Client.Graphics.Clyde
         private void _updateTileMapOnUpdate(ref TileChangedEvent args)
         {
             var gridData = _mapChunkData.GetOrNew(args.Entity);
-            if (gridData.TryGetValue(args.ChunkIndex, out var data))
-                data.Dirty = true;
+            foreach (var change in args.Changes)
+            {
+                if (gridData.TryGetValue(change.ChunkIndex, out var data))
+                    data.Dirty = true;
+            }
         }
 
         private void _updateOnGridCreated(GridStartupEvent ev)
@@ -445,13 +452,57 @@ namespace Robust.Client.Graphics.Clyde
             int gridY,
             Span<Vertex2D> vertexBuffer,
             Span<ushort> indexBuffer,
-            Box2 region)
+            Box2 region,
+            int rotationMirroring)
         {
+            var rLeftBottom = (region.Left, region.Bottom);
+            var rRightBottom = (region.Right, region.Bottom);
+            var rRightTop = (region.Right, region.Top);
+            var rLeftTop = (region.Left, region.Top);
+
+            // The vertices must be changed if there's any rotation or mirroring to the tile
+            if (rotationMirroring != 0)
+            {
+                // Rotate the tile
+                for (int r = 0; r < rotationMirroring % 4; r++)
+                {
+                    (rLeftBottom, rRightBottom, rRightTop, rLeftTop) =
+                        (rLeftTop, rLeftBottom, rRightBottom, rRightTop);
+                }
+
+                // Mirror on the x-axis
+                if (rotationMirroring >= 4)
+                {
+                    if (rotationMirroring % 2 == 0)
+                    {
+                        rLeftBottom = (rLeftBottom.Item1.Equals(region.Left) ? region.Right : region.Left,
+                            rLeftBottom.Item2);
+                        rRightBottom = (rRightBottom.Item1.Equals(region.Left) ? region.Right : region.Left,
+                            rRightBottom.Item2);
+                        rRightTop = (rRightTop.Item1.Equals(region.Left) ? region.Right : region.Left,
+                            rRightTop.Item2);
+                        rLeftTop = (rLeftTop.Item1.Equals(region.Left) ? region.Right : region.Left,
+                            rLeftTop.Item2);
+                    }
+                    else
+                    {
+                        rLeftBottom = (rLeftBottom.Item1,
+                            rLeftBottom.Item2.Equals(region.Bottom) ? region.Top : region.Bottom);
+                        rRightBottom = (rRightBottom.Item1,
+                            rRightBottom.Item2.Equals(region.Bottom) ? region.Top : region.Bottom);
+                        rRightTop = (rRightTop.Item1,
+                            rRightTop.Item2.Equals(region.Bottom) ? region.Top : region.Bottom);
+                        rLeftTop = (rLeftTop.Item1,
+                            rLeftTop.Item2.Equals(region.Bottom) ? region.Top : region.Bottom);
+                    }
+                }
+            }
+
             var vIdx = i * 4;
-            vertexBuffer[vIdx + 0] = new Vertex2D(gridX, gridY, region.Left, region.Bottom, Color.White);
-            vertexBuffer[vIdx + 1] = new Vertex2D(gridX + 1, gridY, region.Right, region.Bottom, Color.White);
-            vertexBuffer[vIdx + 2] = new Vertex2D(gridX + 1, gridY + 1, region.Right, region.Top, Color.White);
-            vertexBuffer[vIdx + 3] = new Vertex2D(gridX, gridY + 1, region.Left, region.Top, Color.White);
+            vertexBuffer[vIdx + 0] = new Vertex2D(gridX, gridY, rLeftBottom.Left, rLeftBottom.Bottom, Color.White);
+            vertexBuffer[vIdx + 1] = new Vertex2D(gridX + 1, gridY, rRightBottom.Right, rRightBottom.Bottom, Color.White);
+            vertexBuffer[vIdx + 2] = new Vertex2D(gridX + 1, gridY + 1, rRightTop.Right, rRightTop.Top, Color.White);
+            vertexBuffer[vIdx + 3] = new Vertex2D(gridX, gridY + 1, rLeftTop.Left, rLeftTop.Top, Color.White);
             var nIdx = i * GetQuadBatchIndexCount();
             var tIdx = (ushort)(i * 4);
             QuadBatchIndexWrite(indexBuffer, ref nIdx, tIdx);

Robust.Client/Graphics/Clyde/Clyde.HLR.cs

@@ -318,7 +318,7 @@ namespace Robust.Client.Graphics.Clyde
                         screenSpriteSize.Y++;
 
                     bool exit = false;
-                    if (entry.Sprite.GetScreenTexture)
+                    if (entry.Sprite.GetScreenTexture && entry.Sprite.PostShader != null)
                     {
                         FlushRenderQueue();
                         var tex = CopyScreenTexture(viewport.RenderTarget);
@@ -369,7 +369,7 @@ namespace Robust.Client.Graphics.Clyde
                     }
                 }
 
-                spriteSystem.Render(entry.Uid, entry.Sprite, _renderHandle.DrawingHandleWorld, eye.Rotation, in entry.WorldRot, in entry.WorldPos);
+                spriteSystem.RenderSprite(new(entry.Uid, entry.Sprite), _renderHandle.DrawingHandleWorld, eye.Rotation, entry.WorldRot, entry.WorldPos);
 
                 if (entry.Sprite.PostShader != null && entityPostRenderTarget != null)
                 {

Robust.Client/Graphics/Clyde/Clyde.Rendering.cs

@@ -613,6 +613,8 @@ namespace Robust.Client.Graphics.Clyde
             EnsureBatchSpaceAvailable(4, GetQuadBatchIndexCount());
             EnsureBatchState(texture, true, GetQuadBatchPrimitiveType(), _queuedShader);
 
+            // TODO RENDERING
+            // It's probably better to do this on the GPU.
             bl = Vector2.Transform(bl, _currentMatrixModel);
             br = Vector2.Transform(br, _currentMatrixModel);
             tr = Vector2.Transform(tr, _currentMatrixModel);

Robust.Client/Graphics/Clyde/Clyde.Sprite.cs

@@ -153,7 +153,7 @@ internal partial class Clyde
 
             // special casing angle = n*pi/2 to avoid box rotation & bounding calculations doesn't seem to give significant speedups.
             data.SpriteScreenBB = TransformCenteredBox(
-                data.Sprite.Bounds,
+                _spriteSystem.GetLocalBounds((data.Uid, data.Sprite)),
                 finalRotation,
                 pos + batch.PreScaleViewOffset,
                 batch.ViewScale);

Robust.Client/Graphics/Clyde/Clyde.Systems.cs

@@ -10,6 +10,7 @@ internal sealed partial class Clyde
     private MapSystem _mapSystem = default!;
     private LightTreeSystem _lightTreeSystem = default!;
     private TransformSystem _transformSystem = default!;
+    private SpriteSystem _spriteSystem = default!;
     private SpriteTreeSystem _spriteTreeSystem = default!;
     private ClientOccluderSystem _occluderSystem = default!;
 
@@ -24,6 +25,7 @@ internal sealed partial class Clyde
         _mapSystem = _entitySystemManager.GetEntitySystem<MapSystem>();
         _lightTreeSystem = _entitySystemManager.GetEntitySystem<LightTreeSystem>();
         _transformSystem = _entitySystemManager.GetEntitySystem<TransformSystem>();
+        _spriteSystem = _entitySystemManager.GetEntitySystem<SpriteSystem>();
         _spriteTreeSystem = _entitySystemManager.GetEntitySystem<SpriteTreeSystem>();
         _occluderSystem = _entitySystemManager.GetEntitySystem<ClientOccluderSystem>();
     }
@@ -33,6 +35,7 @@ internal sealed partial class Clyde
         _mapSystem = null!;
         _lightTreeSystem = null!;
         _transformSystem = null!;
+        _spriteSystem = null!;
         _spriteTreeSystem = null!;
         _occluderSystem = null!;
     }

Robust.Client/Graphics/Clyde/Clyde.Textures.cs

@@ -305,8 +305,8 @@ namespace Robust.Client.Graphics.Clyde
                 IsSrgb = srgb,
                 Name = name,
                 MemoryPressure = memoryPressure,
-                TexturePixelType = pixType
-                // TextureInstance = new WeakReference<ClydeTexture>(instance)
+                TexturePixelType = pixType,
+                TextureInstance = new WeakReference<ClydeTexture>(instance)
             };
 
             _loadedTextures.Add(id, loaded);
@@ -466,15 +466,15 @@ namespace Robust.Client.Graphics.Clyde
         {
             var white = new Image<Rgba32>(1, 1);
             white[0, 0] = new Rgba32(255, 255, 255, 255);
-            _stockTextureWhite = (ClydeTexture) Texture.LoadFromImage(white);
+            _stockTextureWhite = (ClydeTexture) Texture.LoadFromImage(white, name: "StockTextureWhite");
 
             var black = new Image<Rgba32>(1, 1);
             black[0, 0] = new Rgba32(0, 0, 0, 255);
-            _stockTextureBlack = (ClydeTexture) Texture.LoadFromImage(black);
+            _stockTextureBlack = (ClydeTexture) Texture.LoadFromImage(black, name: "StockTextureBlack");
 
             var blank = new Image<Rgba32>(1, 1);
             blank[0, 0] = new Rgba32(0, 0, 0, 0);
-            _stockTextureTransparent = (ClydeTexture) Texture.LoadFromImage(blank);
+            _stockTextureTransparent = (ClydeTexture) Texture.LoadFromImage(blank, name: "StockTextureTransparent");
         }
 
         /// <summary>
@@ -571,7 +571,7 @@ namespace Robust.Client.Graphics.Clyde
             }
         }
 
-        private sealed class LoadedTexture
+        internal sealed class LoadedTexture
         {
             public GLHandle OpenGLObject;
             public int Width;
@@ -582,10 +582,10 @@ namespace Robust.Client.Graphics.Clyde
             public TexturePixelType TexturePixelType;
 
             public Vector2i Size => (Width, Height);
-            // public WeakReference<ClydeTexture> TextureInstance;
+            public required WeakReference<ClydeTexture> TextureInstance;
         }
 
-        private enum TexturePixelType : byte
+        internal enum TexturePixelType : byte
         {
             RenderTarget = 0,
             Rgba32,
@@ -686,5 +686,16 @@ namespace Robust.Client.Graphics.Clyde
                 _ => throw new ArgumentException(nameof(stockTexture))
             };
         }
+
+        public IEnumerable<(ClydeTexture, LoadedTexture)> GetLoadedTextures()
+        {
+            foreach (var loaded in _loadedTextures.Values)
+            {
+                if (!loaded.TextureInstance.TryGetTarget(out var textureInstance))
+                    continue;
+
+                yield return (textureInstance, loaded);
+            }
+        }
     }
 }

Robust.Client/Graphics/Clyde/Clyde.Windowing.cs

@@ -467,7 +467,7 @@ namespace Robust.Client.Graphics.Clyde
             _windowing!.RunOnWindowThread(a);
         }
 
-        public IFileDialogManager? FileDialogImpl => _windowing as IFileDialogManager;
+        public IFileDialogManagerImplementation? FileDialogImpl => _windowing as IFileDialogManagerImplementation;
 
         private abstract class WindowReg
         {

Robust.Client/Graphics/Clyde/ClydeHeadless.cs

@@ -72,6 +72,11 @@ namespace Robust.Client.Graphics.Clyde
             return new DummyTexture((1, 1));
         }
 
+        public IEnumerable<(Clyde.ClydeTexture, Clyde.LoadedTexture)> GetLoadedTextures()
+        {
+            return [];
+        }
+
         public ClydeDebugLayers DebugLayers { get; set; }
 
         public string GetKeyName(Keyboard.Key key) => string.Empty;
@@ -302,7 +307,7 @@ namespace Robust.Client.Graphics.Clyde
             action();
         }
 
-        public IFileDialogManager? FileDialogImpl => null;
+        public IFileDialogManagerImplementation? FileDialogImpl => null;
 
         private sealed class DummyCursor : ICursor
         {

Robust.Client/Graphics/Clyde/GLObjects/Clyde.GLHandle.cs

@@ -11,7 +11,7 @@ namespace Robust.Client.Graphics.Clyde
         ///     Basically just a handle around the integer object handles returned by OpenGL.
         /// </summary>
         [PublicAPI]
-        private struct GLHandle : IEquatable<GLHandle>
+        internal struct GLHandle : IEquatable<GLHandle>
         {
             public readonly uint Handle;
 

Robust.Client/Graphics/Clyde/Windowing/Glfw.Cursors.cs

@@ -87,11 +87,13 @@ namespace Robust.Client.Graphics.Clyde
                 if (cmd.Cursor != default)
                     ptr = _winThreadCursors[cmd.Cursor].Ptr;
 
+#if DEBUG
                 if (_win32Experience)
                 {
                     // Based on a true story.
                     Thread.Sleep(15);
                 }
+#endif
 
                 GLFW.SetCursor(window, ptr);
             }

Robust.Client/Graphics/Clyde/Windowing/Glfw.cs

@@ -23,7 +23,9 @@ namespace Robust.Client.Graphics.Clyde
             private readonly ISawmill _sawmillGlfw;
 
             private bool _glfwInitialized;
+#if DEBUG
             private bool _win32Experience;
+#endif
 
             public GlfwWindowingImpl(Clyde clyde, IDependencyCollection deps)
             {

Robust.Client/Graphics/Clyde/Windowing/Sdl3.FileDialog.cs

@@ -1,5 +1,4 @@
 using System;
-using System.IO;
 using System.Linq;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
@@ -12,31 +11,16 @@ namespace Robust.Client.Graphics.Clyde;
 
 internal partial class Clyde
 {
-    private sealed partial class Sdl3WindowingImpl : IFileDialogManager
+    private sealed partial class Sdl3WindowingImpl : IFileDialogManagerImplementation
     {
-        public async Task<Stream?> OpenFile(FileDialogFilters? filters = null)
+        public async Task<string?> OpenFile(FileDialogFilters? filters)
         {
-            var fileName = await ShowFileDialogOfType(SDL.SDL_FILEDIALOG_OPENFILE, filters);
-            if (fileName == null)
-                return null;
-
-            return File.OpenRead(fileName);
+            return await ShowFileDialogOfType(SDL.SDL_FILEDIALOG_OPENFILE, filters);
         }
 
-        public async Task<(Stream fileStream, bool alreadyExisted)?> SaveFile(FileDialogFilters? filters = null, bool truncate = true)
+        public async Task<string?> SaveFile(FileDialogFilters? filters)
         {
-            var fileName = await ShowFileDialogOfType(SDL.SDL_FILEDIALOG_SAVEFILE, filters);
-            if (fileName == null)
-                return null;
-
-            try
-            {
-                return (File.Open(fileName, truncate ? FileMode.Truncate : FileMode.Open), true);
-            }
-            catch (FileNotFoundException)
-            {
-                return (File.Open(fileName, FileMode.Create), false);
-            }
+            return await ShowFileDialogOfType(SDL.SDL_FILEDIALOG_SAVEFILE, filters);
         }
 
         private unsafe Task<string?> ShowFileDialogOfType(int type, FileDialogFilters? filters)
@@ -74,6 +58,8 @@ internal partial class Clyde
                     NativeMemory.Free(filter.name);
                     NativeMemory.Free(filter.pattern);
                 }
+
+                NativeMemory.Free(filtersAlloc);
             }
 
             return task;

Robust.Client/Graphics/IClydeInternal.cs

@@ -54,6 +54,7 @@ namespace Robust.Client.Graphics
         IClydeDebugStats DebugStats { get; }
 
         Texture GetStockTexture(ClydeStockTexture stockTexture);
+        IEnumerable<(Clyde.Clyde.ClydeTexture, Clyde.Clyde.LoadedTexture)> GetLoadedTextures();
 
         ClydeDebugLayers DebugLayers { get; set; }
 
@@ -70,6 +71,6 @@ namespace Robust.Client.Graphics
 
         void RunOnWindowThread(Action action);
 
-        IFileDialogManager? FileDialogImpl { get; }
+        IFileDialogManagerImplementation? FileDialogImpl { get; }
     }
 }

Robust.Client/Localization/ClientLocalizationManager.cs

@@ -0,0 +1,33 @@
+using Robust.Shared.IoC;
+using Robust.Shared.Localization;
+using Robust.Shared.Utility;
+
+namespace Robust.Client.Localization;
+
+internal sealed class ClientLocalizationManager : LocalizationManager, ILocalizationManagerInternal
+{
+    [Dependency] private readonly IReloadManager _reload = default!;
+
+    void ILocalizationManager.Initialize() => Initialize();
+
+    /// <inheritdoc/>
+    public override void Initialize()
+    {
+        base.Initialize();
+
+        _reload.Register(LocaleDirPath, "*.ftl");
+
+        _reload.OnChanged += OnReload;
+    }
+
+    /// <summary>
+    /// Handles Fluent hot reloading via LocalizationManager.ReloadLocalizations()
+    /// </summary>
+    private void OnReload(ResPath args)
+    {
+        if (args.Extension != "ftl")
+            return;
+
+        ReloadLocalizations();
+    }
+}

Robust.Client/Physics/DebugPhysicsIslandSystem.cs

@@ -47,7 +47,7 @@ namespace Robust.Client.Physics
          * This will draw above every body involved in a particular island solve.
          */
 
-        public readonly Queue<(TimeSpan Time, List<PhysicsComponent> Bodies)> IslandSolve = new();
+        public readonly Queue<(TimeSpan Time, List<Entity<PhysicsComponent, TransformComponent>> Bodies)> IslandSolve = new();
         public const float SolveDuration = 0.1f;
 
         public override void Initialize()

Robust.Client/Physics/PhysicsSystem.Predict.cs

@@ -90,9 +90,10 @@ public sealed partial class PhysicsSystem
         // existing contacts for predicted entities before performing any actual prediction.
 
         var contacts = new List<Contact>();
-        var maps = new HashSet<EntityUid>();
 
         var enumerator = AllEntityQuery<PredictedPhysicsComponent, PhysicsComponent, TransformComponent>();
+        _broadphase.FindNewContacts();
+
         while (enumerator.MoveNext(out _, out var physics, out var xform))
         {
             DebugTools.Assert(physics.Predict);
@@ -100,10 +101,6 @@ public sealed partial class PhysicsSystem
             if (xform.MapUid is not { } map)
                 continue;
 
-            if (maps.Add(map) && PhysMapQuery.TryGetComponent(map, out var physMap) &&
-                MapQuery.TryGetComponent(map, out var mapComp))
-                _broadphase.FindNewContacts(physMap, mapComp.MapId);
-
             contacts.AddRange(physics.Contacts);
         }
 

Robust.Client/Physics/PhysicsSystem.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using JetBrains.Annotations;
+using Robust.Shared.Collections;
 using Robust.Shared.GameObjects;
 using Robust.Shared.IoC;
 using Robust.Shared.Physics;
@@ -23,21 +24,23 @@ namespace Robust.Client.Physics
             SimulateWorld(frameTime, _gameTiming.InPrediction);
         }
 
-        protected override void Cleanup(PhysicsMapComponent component, float frameTime)
+        protected override void Cleanup(float frameTime)
         {
-            var toRemove = new List<Entity<PhysicsComponent>>();
+            var toRemove = new ValueList<Entity<PhysicsComponent, TransformComponent>>();
 
             // Because we're not predicting 99% of bodies its sleep timer never gets incremented so we'll just do it ourselves.
             // (and serializing it over the network isn't necessary?)
             // This is a client-only problem.
             // Also need to suss out having the client build the island anyway and just... not solving it?
-            foreach (var body in component.AwakeBodies)
+            foreach (var ent in AwakeBodies)
             {
+                var body = ent.Comp1;
+
                 if (!body.SleepingAllowed || body.LinearVelocity.Length() > LinearToleranceSqr / 2f || body.AngularVelocity * body.AngularVelocity > AngularToleranceSqr / 2f) continue;
                 body.SleepTime += frameTime;
                 if (body.SleepTime > TimeToSleep)
                 {
-                    toRemove.Add(new Entity<PhysicsComponent>(body.Owner, body));
+                    toRemove.Add(ent);
                 }
             }
 
@@ -46,37 +49,38 @@ namespace Robust.Client.Physics
                 SetAwake(body, false);
             }
 
-            base.Cleanup(component, frameTime);
+            base.Cleanup(frameTime);
         }
 
-        protected override void UpdateLerpData(PhysicsMapComponent component, List<PhysicsComponent> bodies, EntityQuery<TransformComponent> xformQuery)
+        protected override void UpdateLerpData(List<Entity<PhysicsComponent, TransformComponent>> bodies)
         {
-            foreach (var body in bodies)
+            foreach (var bodyEnt in bodies)
             {
+                var body = bodyEnt.Comp1;
+                var xform = bodyEnt.Comp2;
+
                 if (body.BodyType == BodyType.Static ||
-                    component.LerpData.TryGetValue(body.Owner, out var lerpData) ||
-                    !xformQuery.TryGetComponent(body.Owner, out var xform) ||
-                    lerpData.ParentUid == xform.ParentUid)
+                    LerpData.TryGetValue(bodyEnt, out var lerpData) ||
+                    lerpData == xform.ParentUid)
                 {
                     continue;
                 }
 
-                component.LerpData[xform.Owner] = (xform.ParentUid, xform.LocalPosition, xform.LocalRotation);
+                LerpData[bodyEnt.Owner] = xform.ParentUid;
             }
         }
 
         /// <summary>
         /// Flush all of our lerping data.
         /// </summary>
-        protected override void FinalStep(PhysicsMapComponent component)
+        protected override void FinalStep()
         {
-            base.FinalStep(component);
-            var xformQuery = GetEntityQuery<TransformComponent>();
+            base.FinalStep();
 
-            foreach (var (uid, (parentUid, position, rotation)) in component.LerpData)
+            foreach (var (uid, parentUid) in LerpData)
             {
-                if (!xformQuery.TryGetComponent(uid, out var xform) ||
-                    !parentUid.IsValid())
+                // Can't just re-use xform from before as movement events may cause event subs to fire.
+                if (!XformQuery.TryGetComponent(uid, out var xform) || !parentUid.IsValid())
                 {
                     continue;
                 }
@@ -85,7 +89,7 @@ namespace Robust.Client.Physics
                 _transform.SetLocalPositionRotation(uid, xform.LocalPosition, xform.LocalRotation, xform);
             }
 
-            component.LerpData.Clear();
+            LerpData.Clear();
         }
     }
 }

Robust.Client/Placement/IPlacementManager.cs

@@ -24,10 +24,20 @@ namespace Robust.Client.Placement
         Direction Direction { get; set; }
 
         /// <summary>
-        /// Gets called when Direction changed (presently for EntitySpawnWindow UI)
+        /// Whether a tile placement should be mirrored or not.
+        /// </summary>
+        bool Mirrored { get; set; }
+
+        /// <summary>
+        /// Gets called when Direction changed (presently for EntitySpawnWindow/TileSpawnWindow UI)
         /// </summary>
         event EventHandler DirectionChanged;
 
+        /// <summary>
+        /// Gets called when Mirrored changed (presently for TileSpawnWindow UI)
+        /// </summary>
+        event EventHandler MirroredChanged;
+
         /// <summary>
         /// Gets called when the PlacementManager changed its build/erase mode or when the hijacks changed
         /// </summary>

Robust.Client/Placement/PlacementManager.cs

@@ -47,6 +47,7 @@ namespace Robust.Client.Placement
 
         private SharedMapSystem Maps => EntityManager.System<SharedMapSystem>();
         private SharedTransformSystem XformSystem => EntityManager.System<SharedTransformSystem>();
+        private SpriteSystem Sprite => EntityManager.System<SpriteSystem>();
 
         /// <summary>
         ///     How long before a pending tile change is dropped.
@@ -174,6 +175,18 @@ namespace Robust.Client.Placement
 
         private Direction _direction = Direction.South;
 
+        private bool _mirrored;
+
+        public bool Mirrored
+        {
+            get => _mirrored;
+            set
+            {
+                _mirrored = value;
+                MirroredChanged?.Invoke(this, EventArgs.Empty);
+            }
+        }
+
         /// <inheritdoc />
         public Direction Direction
         {
@@ -188,6 +201,9 @@ namespace Robust.Client.Placement
         /// <inheritdoc />
         public event EventHandler? DirectionChanged;
 
+        /// <inheritdoc />
+        public event EventHandler? MirroredChanged;
+
         private PlacementOverlay _drawOverlay = default!;
         private bool _isActive;
 
@@ -344,18 +360,27 @@ namespace Robust.Client.Placement
 
         private void HandleTileChanged(ref TileChangedEvent args)
         {
-            var coords = Maps.GridTileToLocal(
-                args.NewTile.GridUid,
-                EntityManager.GetComponent<MapGridComponent>(args.NewTile.GridUid),
-                args.NewTile.GridIndices);
+            foreach (var change in args.Changes)
+            {
+                var coords = Maps.GridTileToLocal(
+                args.Entity,
+                args.Entity.Comp,
+                change.GridIndices);
 
-            _pendingTileChanges.RemoveAll(c => c.Item1 == coords);
+                _pendingTileChanges.RemoveAll(c => c.Item1 == coords);
+            }
         }
 
         /// <inheritdoc />
         public event EventHandler? PlacementChanged;
 
         public void Clear()
+        {
+            ClearWithoutDeactivation();
+            IsActive = false;
+        }
+
+        private void ClearWithoutDeactivation()
         {
             PlacementChanged?.Invoke(this, EventArgs.Empty);
             Hijack = null;
@@ -365,7 +390,6 @@ namespace Robust.Client.Placement
             CurrentMode = null;
             DeactivateSpecialPlacement();
             _placenextframe = false;
-            IsActive = false;
             Eraser = false;
             EraserRect = null;
             PlacementOffset = Vector2i.Zero;
@@ -480,18 +504,17 @@ namespace Robust.Client.Placement
 
         public void BeginHijackedPlacing(PlacementInformation info, PlacementHijack? hijack = null)
         {
-            Clear();
+            ClearWithoutDeactivation();
 
-            CurrentPermission = info;
-
-            if (!_modeDictionary.TryFirstOrNull(pair => pair.Key.Equals(CurrentPermission.PlacementOption), out KeyValuePair<string, Type>? placeMode))
+            if (info.PlacementOption is not { } option || !_modeDictionary.TryGetValue(option, out var placeMode))
             {
-                _sawmill.Log(LogLevel.Warning, $"Invalid placement mode `{CurrentPermission.PlacementOption}`");
+                _sawmill.Log(LogLevel.Warning, $"Invalid placement mode `{info.PlacementOption}`");
                 Clear();
                 return;
             }
 
-            CurrentMode = (PlacementMode) Activator.CreateInstance(placeMode.Value.Value, this)!;
+            CurrentPermission = info;
+            CurrentMode = (PlacementMode) Activator.CreateInstance(placeMode, this)!;
 
             if (hijack != null)
             {
@@ -689,11 +712,11 @@ namespace Robust.Client.Placement
             CurrentPlacementOverlayEntity = null;
         }
 
-        private SpriteComponent SetupPlacementOverlayEntity()
+        private Entity<SpriteComponent> SetupPlacementOverlayEntity()
         {
             EnsureNoPlacementOverlayEntity();
             CurrentPlacementOverlayEntity = EntityManager.SpawnEntity(null, MapCoordinates.Nullspace);
-            return EntityManager.EnsureComponent<SpriteComponent>(CurrentPlacementOverlayEntity.Value);
+            return (CurrentPlacementOverlayEntity.Value, EntityManager.EnsureComponent<SpriteComponent>(CurrentPlacementOverlayEntity.Value));
         }
 
         private void PreparePlacement(string templateName)
@@ -710,10 +733,16 @@ namespace Robust.Client.Placement
                 EntityManager.GetComponent<MetaDataComponent>(CurrentPlacementOverlayEntity.Value));
         }
 
-        public void PreparePlacementSprite(SpriteComponent sprite)
+        public void PreparePlacementSprite(Entity<SpriteComponent> sprite)
         {
             var sc = SetupPlacementOverlayEntity();
-            sc.CopyFrom(sprite);
+            Sprite.CopySprite(sprite.AsNullable(), sc.AsNullable());
+        }
+
+        [Obsolete("Use the Entity<SpriteComponent> overload.")]
+        public void PreparePlacementSprite(SpriteComponent sprite)
+        {
+            PreparePlacementSprite((sprite.Owner, sprite));
         }
 
         public void PreparePlacementTexList(List<IDirectionalTextureProvider>? texs, bool noRot, EntityPrototype? prototype)
@@ -724,27 +753,27 @@ namespace Robust.Client.Placement
                 // This one covers most cases (including Construction)
                 foreach (var v in texs)
                 {
-                    if (v is RSI.State)
+                    if (v is RSI.State st)
                     {
-                        var st = (RSI.State) v;
-                        sc.AddLayer(st.StateId, st.RSI);
+                        Sprite.AddRsiLayer(sc.AsNullable(), st.StateId, st.RSI);
                     }
                     else
                     {
                         // Fallback
-                        sc.AddLayer(v.Default);
+                        Sprite.AddTextureLayer(sc.AsNullable(), v.Default);
                     }
                 }
             }
             else
             {
-                sc.AddLayer(new ResPath("/Textures/Interface/tilebuildoverlay.png"));
+                Sprite.AddTextureLayer(sc.AsNullable(), new ResPath("/Textures/Interface/tilebuildoverlay.png"));
             }
-            sc.NoRotation = noRot;
+
+            sc.Comp.NoRotation = noRot;
 
             if (prototype != null && prototype.TryGetComponent<SpriteComponent>("Sprite", out var spriteComp))
             {
-                sc.Scale = spriteComp.Scale;
+                Sprite.SetScale(sc.AsNullable(), spriteComp.Scale);
             }
 
         }
@@ -752,7 +781,7 @@ namespace Robust.Client.Placement
         private void PreparePlacementTile()
         {
             var sc = SetupPlacementOverlayEntity();
-            sc.AddLayer(new ResPath("/Textures/Interface/tilebuildoverlay.png"));
+            Sprite.AddTextureLayer(sc.AsNullable(), new ResPath("/Textures/Interface/tilebuildoverlay.png"));
 
             IsActive = true;
         }
@@ -772,7 +801,9 @@ namespace Robust.Client.Placement
                     var grid = EntityManager.GetComponent<MapGridComponent>(gridId);
 
                     // no point changing the tile to the same thing.
-                    if (Maps.GetTileRef(gridId, grid, coordinates).Tile.TypeId == CurrentPermission.TileType)
+                    var tileRef = Maps.GetTileRef(gridId, grid, coordinates).Tile;
+                    if (tileRef.TypeId == CurrentPermission.TileType &&
+                        tileRef.RotationMirroring == Tile.DirectionToByte(Direction) + (Mirrored ? 4 : 0))
                         return;
                 }
 
@@ -796,9 +827,14 @@ namespace Robust.Client.Placement
             };
 
             if (CurrentPermission.IsTile)
+            {
                 message.TileType = CurrentPermission.TileType;
+                message.Mirrored = Mirrored;
+            }
             else
+            {
                 message.EntityTemplateName = CurrentPermission.EntityType;
+            }
 
             // world x and y
             message.NetCoordinates = EntityManager.GetNetCoordinates(coordinates);

Robust.Client/Placement/PlacementMode.cs

@@ -126,7 +126,7 @@ namespace Robust.Client.Placement
 
                 sprite.Color = IsValidPosition(coordinate) ? ValidPlaceColor : InvalidPlaceColor;
                 var rot = args.Viewport.Eye?.Rotation ?? default;
-                spriteSys.Render(uid.Value, sprite, args.WorldHandle, rot, worldRot, worldPos);
+                spriteSys.RenderSprite((uid.Value, sprite), args.WorldHandle, rot, worldRot, worldPos);
             }
         }
 

Robust.Client/Player/PlayerManager.cs

@@ -166,7 +166,7 @@ namespace Robust.Client.Player
             {
                 if (_client.RunLevel != ClientRunLevel.SinglePlayerGame)
                     Sawmill.Warning($"Attaching local player to an entity {EntManager.ToPrettyString(uid)} without an eye. This eye will not be netsynced and may cause issues.");
-                var eye = (EyeComponent) Factory.GetComponent(typeof(EyeComponent));
+                var eye = Factory.GetComponent<EyeComponent>();
                 eye.NetSyncEnabled = false;
                 EntManager.AddComponent(uid.Value, eye);
             }

Robust.Client/Prototypes/ClientPrototypeManager.cs

@@ -13,7 +13,9 @@ namespace Robust.Client.Prototypes
     public sealed class ClientPrototypeManager : PrototypeManager
     {
         [Dependency] private readonly INetManager _netManager = default!;
+#pragma warning disable CS0414
         [Dependency] private readonly IClientGameTiming _timing = default!;
+#pragma warning restore CS0414
         [Dependency] private readonly IGameControllerInternal _controller = default!;
         [Dependency] private readonly IReloadManager _reload = default!;
 

Robust.Client/ResourceManagement/ResourceCache.Preload.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using System.Threading.Tasks;
@@ -8,6 +9,7 @@ using Robust.Client.Graphics;
 using Robust.Client.Utility;
 using Robust.Shared;
 using Robust.Shared.Audio;
+using Robust.Shared.Collections;
 using Robust.Shared.Configuration;
 using Robust.Shared.ContentPack;
 using Robust.Shared.Graphics;
@@ -59,7 +61,14 @@ namespace Robust.Client.ResourceManagement
             {
                 try
                 {
-                    TextureResource.LoadPreTexture(_manager, data);
+                    TextureResource.LoadTextureParameters(_manager, data);
+                    if (!data.LoadParameters.Preload)
+                    {
+                        data.Skip = true;
+                        return;
+                    }
+
+                    TextureResource.LoadPreTextureData(_manager, data);
                 }
                 catch (Exception e)
                 {
@@ -72,7 +81,7 @@ namespace Robust.Client.ResourceManagement
 
             foreach (var data in texList)
             {
-                if (data.Bad)
+                if (data.Bad || data.Skip)
                     continue;
 
                 try
@@ -87,6 +96,7 @@ namespace Robust.Client.ResourceManagement
             }
 
             var errors = 0;
+            var skipped = 0;
             foreach (var data in texList)
             {
                 if (data.Bad)
@@ -95,6 +105,12 @@ namespace Robust.Client.ResourceManagement
                     continue;
                 }
 
+                if (data.Skip)
+                {
+                    skipped += 1;
+                    continue;
+                }
+
                 try
                 {
                     var texResource = new TextureResource();
@@ -110,9 +126,10 @@ namespace Robust.Client.ResourceManagement
             }
 
             sawmill.Debug(
-                "Preloaded {CountLoaded} textures ({CountErrored} errored) in {LoadTime}",
-                texList.Length,
+                "Preloaded {CountLoaded} textures ({CountErrored} errored, {CountSkipped} skipped) in {LoadTime}",
+                texList.Length - skipped - errors,
                 errors,
+                skipped,
                 sw.Elapsed);
         }
 
@@ -176,65 +193,143 @@ namespace Robust.Client.ResourceManagement
             // TODO allow RSIs to opt out (useful for very big & rare RSIs)
             // TODO combine with (non-rsi) texture atlas?
 
-            Array.Sort(atlasList, (b, a) => (b.AtlasSheet?.Height ?? 0).CompareTo(a.AtlasSheet?.Height ?? 0));
+            // We now need to insert the RSIs into the atlas. This specific problem is 2BP|O|F - the items are oriented
+            // and cutting is free. The sorting is done by a slightly modified FFDH algorithm. The algorithm is exactly
+            // the same as the standard FFDH algorithm with one main difference: We create new "levels" above placed
+            // blocks. For example if the first block was 10x20, then the second was 10x10 units, we would create a
+            // 10x10 level above the second block that would be treated as a normal level. This increases the packing
+            // efficiency from ~85% to ~95% with very little extra computational effort. The algorithm appears to be
+            // ~97% effective for storing SS14s RSIs.
+            //
+            // Here are some more resources about the strip packing problem!
+            //   -  https://en.wikipedia.org/w/index.php?title=Strip_packing_problem&oldid=1263496949#First-fit_decreasing-height_(FFDH)
+            //   -  https://www.csc.liv.ac.uk/~epa/surveyhtml.html
+            //   -  https://www.dei.unipd.it/~fisch/ricop/tesi/tesi_dottorato_Lodi_1999.pdf
+
+            // The array must be sorted from biggest to smallest first.
+            Array.Sort(atlasList, (b, a) => a.AtlasSheet.Height.CompareTo(b.AtlasSheet.Height));
 
-            // Each RSI sub atlas has a different size.
-            // Even if we iterate through them once to estimate total area, I have NFI how to sanely estimate an optimal square-texture size.
-            // So fuck it, just default to letting it be as large as it needs to and crop it as needed?
             var maxSize = Math.Min(GL.GetInteger(GetPName.MaxTextureSize), _configurationManager.GetCVar(CVars.ResRSIAtlasSize));
-            var sheet = new Image<Rgba32>(maxSize, maxSize);
 
-            var deltaY = 0;
-            Vector2i offset = default;
-            int finalized = -1;
-            int atlasCount = 0;
-            for (int i = 0; i < atlasList.Length; i++)
+            // THIS IS NOT GUARANTEED TO HAVE ANY PARTICULARLY LOGICAL ORDERING.
+            // E.G you could have atlas 1 RSIs appear *before* you're done seeing atlas 2 RSIs.
+            var levels = new ValueList<Level>();
+
+            // List of all the image atlases.
+            var imageAtlases = new ValueList<Image<Rgba32>>();
+
+            // List of all the actual atlases.
+            var finalAtlases = new ValueList<OwnedTexture>();
+
+            // Number of total pixels in each atlas.
+            var finalPixels = new ValueList<int>();
+
+            // First we just find the location of all the RSIs in the atlas before actually placing them.
+            // This allows us to effectively determine how much space we need to allocate for the images.
+            var currentHeight = 0;
+            var currentAtlasIndex = 0;
+            foreach (var rsi in atlasList)
             {
-                var rsi = atlasList[i];
-                if (rsi.Bad)
+                var insertHeight = rsi.AtlasSheet.Height;
+                var insertWidth = rsi.AtlasSheet.Width;
+
+                var found = false;
+                for (var i = 0; i < levels.Count && !found; i++)
+                {
+                    var levelPosition = levels[i].Position;
+                    var levelWidth = levels[i].Width;
+                    var levelHeight = levels[i].Height;
+
+                    // Check if it can fit in this level.
+                    if (levelHeight < insertHeight || levelWidth + insertWidth > levels[i].MaxWidth)
+                        continue;
+
+                    found = true;
+
+                    levels[i].Width += insertWidth;
+                    rsi.AtlasOffset = levelPosition + new Vector2i(levelWidth, 0);
+                    levels[i].RSIList.Add(rsi);
+
+                    // Creating the extra "free" space above blocks that can be used for inserting more items.
+                    // This differs from the FFDH spec which just ignores this space.
+                    Debug.Assert(levelHeight >= insertHeight); // Must be true because the array needs to be sorted
+                    if (levelHeight - insertHeight == 0)
+                        continue;
+
+                    var freeLevel = new Level
+                    {
+                        AtlasId = levels[i].AtlasId,
+                        Position = levelPosition + new Vector2i(levelWidth, insertHeight),
+                        Height = levelHeight - insertHeight,
+                        Width = 0,
+                        MaxWidth = insertWidth,
+                        RSIList = [ ]
+                    };
+
+                    levels.Add(freeLevel);
+                }
+
+                if (found)
                     continue;
 
-                DebugTools.Assert(rsi.AtlasSheet.Width < sheet.Width);
-                DebugTools.Assert(rsi.AtlasSheet.Height < sheet.Height);
-
-                if (offset.X + rsi.AtlasSheet.Width > sheet.Width)
+                // Ran out of space, we need to move on to the next atlas.
+                // This also isn't in the normal FFDH algorithm (obviously) but its close enough.
+                if (currentHeight + insertHeight > maxSize)
                 {
-                    offset.X = 0;
-                    offset.Y += deltaY;
+                    imageAtlases.Add(new Image<Rgba32>(maxSize, currentHeight));
+                    finalPixels.Add(0);
+                    currentHeight = 0;
+                    currentAtlasIndex++;
                 }
 
-                if (offset.Y + rsi.AtlasSheet.Height > sheet.Height)
-                {
-                    FinalizeMetaAtlas(i-1, sheet);
-                    sheet = new Image<Rgba32>(maxSize, maxSize);
-                    deltaY = 0;
-                    offset = default;
-                }
+                rsi.AtlasOffset = new Vector2i(0, currentHeight);
 
-                deltaY = Math.Max(deltaY, rsi.AtlasSheet.Height);
-                var box = new UIBox2i(0, 0, rsi.AtlasSheet.Width, rsi.AtlasSheet.Height);
-                rsi.AtlasSheet.Blit(box, sheet, offset);
-                rsi.AtlasOffset = offset;
-                offset.X += rsi.AtlasSheet.Width;
+                var newLevel = new Level
+                {
+                    AtlasId = currentAtlasIndex,
+                    Position = new Vector2i(0, currentHeight),
+                    Height = insertHeight,
+                    Width = insertWidth,
+                    MaxWidth = maxSize,
+                    RSIList = [ rsi ]
+                };
+                levels.Add(newLevel);
+
+                currentHeight += insertHeight;
             }
 
-            var height = offset.Y + deltaY;
-            var croppedSheet = new Image<Rgba32>(maxSize, height);
-            sheet.Blit(new UIBox2i(0, 0, maxSize, height), croppedSheet, default);
-            FinalizeMetaAtlas(atlasList.Length - 1, croppedSheet);
+            // This allocation takes a long time.
+            imageAtlases.Add(new Image<Rgba32>(maxSize, currentHeight));
+            finalPixels.Add(0);
 
-            void FinalizeMetaAtlas(int toIndex, Image<Rgba32> sheet)
+            // Put all textures on the atlases
+            foreach (var level in levels)
             {
-                var fromIndex = finalized + 1;
-                var atlas = Clyde.LoadTextureFromImage(sheet, $"Meta atlas {fromIndex}-{toIndex}");
-                for (int i = fromIndex; i <= toIndex; i++)
+                foreach (var rsi in level.RSIList)
                 {
-                    var rsi = atlasList[i];
-                    rsi.AtlasTexture = atlas;
-                }
+                    var box = new UIBox2i(0, 0, rsi.AtlasSheet.Width, rsi.AtlasSheet.Height);
 
-                finalized = toIndex;
-                atlasCount++;
+                    rsi.AtlasSheet.Blit(box, imageAtlases[level.AtlasId], rsi.AtlasOffset);
+                    finalPixels[level.AtlasId] += rsi.AtlasSheet.Width * rsi.AtlasSheet.Height;
+                }
+            }
+
+            // Finalize the atlases.
+            for (var i = 0; i < imageAtlases.Count; i++)
+            {
+                var atlasTexture = Clyde.LoadTextureFromImage(imageAtlases[i], $"Meta atlas {i}");
+                finalAtlases.Add(atlasTexture);
+
+                sawmill.Debug($"(Meta atlas {i}) - cropped utilization: {(float)finalPixels[i] / (maxSize * imageAtlases[i].Height):P2}, fill percentage: {(float)imageAtlases[i].Height / maxSize:P2}");
+            }
+
+            // Finally, reference the actual atlas from the RSIs.
+            foreach (var level in levels)
+            {
+                foreach (var rsi in level.RSIList)
+                {
+                    rsi.AtlasTexture = finalAtlases[level.AtlasId];
+                }
             }
 
             Parallel.ForEach(rsiList, data =>
@@ -279,7 +374,7 @@ namespace Robust.Client.ResourceManagement
             sawmill.Debug(
                 "Preloaded {CountLoaded} RSIs into {CountAtlas} Atlas(es?) ({CountNotAtlas} not atlassed, {CountErrored} errored) in {LoadTime}",
                 rsiList.Length,
-                atlasCount,
+                finalAtlases.Count,
                 nonAtlasList.Length,
                 errors,
                 sw.Elapsed);
@@ -290,4 +385,38 @@ namespace Robust.Client.ResourceManagement
             return rsi.MetaAtlas && rsi.LoadParameters == TextureLoadParameters.Default;
         }
     }
+
+    /// <summary>
+    ///     A "Level" to place boxes. Similar to FFDH levels, but with more parameters so we can fit in "free" levels
+    ///     above placed boxes.
+    /// </summary>
+    internal sealed class Level
+    {
+        /// <summary>
+        ///     Index of the atlas this is located.
+        /// </summary>
+        public required int AtlasId;
+        /// <summary>
+        ///     Bottom left of the location for the RSIs.
+        /// </summary>
+        public required Vector2i Position;
+        /// <summary>
+        ///     The current width of the level.
+        /// </summary>
+        /// <remarks>This can (and will) be 0. Will change.</remarks>
+        public required int Width;
+        /// <summary>
+        ///     The current height of the level.
+        /// </summary>
+        /// <remarks>This value should never change.</remarks>
+        public required int Height;
+        /// <summary>
+        ///     Maximum width of the level.
+        /// </summary>
+        public required int MaxWidth;
+        /// <summary>
+        ///     List of all the RSIs stored in this level. RSIs are ordered from tallest to smallest per level.
+        /// </summary>
+        public required List<RSIResource.LoadStepData> RSIList;
+    }
 }

Robust.Client/ResourceManagement/ResourceTypes/AudioResource.cs

@@ -1,8 +1,8 @@
 using System;
 using System.IO;
+using System.Linq;
 using System.Threading;
 using Robust.Client.Audio;
-using Robust.Shared.Audio;
 using Robust.Shared.ContentPack;
 using Robust.Shared.IoC;
 using Robust.Shared.Utility;
@@ -11,6 +11,13 @@ namespace Robust.Client.ResourceManagement;
 
 public sealed class AudioResource : BaseResource
 {
+    // from: https://en.wikipedia.org/wiki/List_of_file_signatures
+    private static readonly byte[] OggSignature = "OggS"u8.ToArray();
+    private static readonly byte[] RiffSignature = "RIFF"u8.ToArray();
+    private const int WavSignatureStart = 8; // RIFF????
+    private static readonly byte[] WavSignature = "WAVE"u8.ToArray();
+    private const int MaxSignatureLength = 12; // RIFF????WAVE
+
     public AudioStream AudioStream { get; private set; } = default!;
 
     public void Load(AudioStream stream)
@@ -28,14 +35,19 @@ public sealed class AudioResource : BaseResource
         }
 
         using var fileStream = cache.ContentFileRead(path);
+        var seekableStream = fileStream.CanSeek ? fileStream : fileStream.CopyToMemoryStream();
+        byte[] signature = seekableStream.ReadExact(MaxSignatureLength);
+        seekableStream.Seek(0, SeekOrigin.Begin);
+
         var audioManager = dependencies.Resolve<IAudioInternal>();
-        if (path.Extension == "ogg")
+        if (signature[..OggSignature.Length].SequenceEqual(OggSignature))
         {
-            AudioStream = audioManager.LoadAudioOggVorbis(fileStream, path.ToString());
+            AudioStream = audioManager.LoadAudioOggVorbis(seekableStream, path.ToString());
         }
-        else if (path.Extension == "wav")
+        else if (signature[..RiffSignature.Length].SequenceEqual(RiffSignature)
+                 && signature[WavSignatureStart..MaxSignatureLength].SequenceEqual(WavSignature))
         {
-            AudioStream = audioManager.LoadAudioWav(fileStream, path.ToString());
+            AudioStream = audioManager.LoadAudioWav(seekableStream, path.ToString());
         }
         else
         {

Robust.Client/ResourceManagement/ResourceTypes/TextureResource.cs

@@ -32,18 +32,22 @@ namespace Robust.Client.ResourceManagement
 
             var data = new LoadStepData {Path = path};
 
-            LoadPreTexture(dependencies.Resolve<IResourceManager>(), data);
+            LoadTextureParameters(dependencies.Resolve<IResourceManager>(), data);
+            LoadPreTextureData(dependencies.Resolve<IResourceManager>(), data);
             LoadTexture(dependencies.Resolve<IClyde>(), data);
             LoadFinish(dependencies.Resolve<IResourceCache>(), data);
         }
 
-        internal static void LoadPreTexture(IResourceManager cache, LoadStepData data)
+        internal static void LoadPreTextureData(IResourceManager cache, LoadStepData data)
         {
             using (var stream = cache.ContentFileRead(data.Path))
             {
                 data.Image = Image.Load<Rgba32>(stream);
             }
+        }
 
+        internal static void LoadTextureParameters(IResourceManager cache, LoadStepData data)
+        {
             data.LoadParameters = TryLoadTextureParameters(cache, data.Path) ?? TextureLoadParameters.Default;
         }
 
@@ -95,7 +99,8 @@ namespace Robust.Client.ResourceManagement
         {
             var data = new LoadStepData {Path = path};
 
-            LoadPreTexture(dependencies.Resolve<IResourceManager>(), data);
+            LoadTextureParameters(dependencies.Resolve<IResourceManager>(), data);
+            LoadPreTextureData(dependencies.Resolve<IResourceManager>(), data);
 
             if (data.Image.Width == Texture.Width && data.Image.Height == Texture.Height)
             {
@@ -119,6 +124,7 @@ namespace Robust.Client.ResourceManagement
             public Image<Rgba32> Image = default!;
             public TextureLoadParameters LoadParameters;
             public OwnedTexture Texture = default!;
+            public bool Skip;
             public bool Bad;
         }
 

Robust.Client/Upload/Commands/LoadPrototypeCommand.cs

@@ -22,7 +22,7 @@ public sealed class LoadPrototypeCommand : IConsoleCommand
         var dialogManager = IoCManager.Resolve<IFileDialogManager>();
         var loadManager = IoCManager.Resolve<IGamePrototypeLoadManager>();
 
-        var stream = await dialogManager.OpenFile();
+        var stream = await dialogManager.OpenFile(access: FileAccess.Read);
         if (stream is null)
             return;
 

Robust.Client/Upload/Commands/UploadFileCommand.cs

@@ -1,3 +1,4 @@
+using System.IO;
 using Robust.Client.UserInterface;
 using Robust.Shared;
 using Robust.Shared.Configuration;
@@ -36,7 +37,7 @@ public sealed class UploadFileCommand : IConsoleCommand
         var path = new ResPath(args[0]).ToRelativePath();
 
         var filters = new FileDialogFilters(new FileDialogFilters.Group(path.Extension));
-        await using var file = await _dialog.OpenFile(filters);
+        await using var file = await _dialog.OpenFile(filters, FileAccess.Read);
 
         if (file == null)
         {

Robust.Client/UserInterface/Control.cs

@@ -994,6 +994,9 @@ namespace Robust.Client.UserInterface
 
         internal int DoFrameUpdateRecursive(FrameEventArgs args)
         {
+            if (!Visible)
+                return 0;
+
             var total = 1;
             FrameUpdate(args);
 

Robust.Client/UserInterface/Controllers/Implementations/TileSpawningUIController.cs

@@ -1,8 +1,10 @@
 using System;
 using System.Collections.Generic;
+using System.Drawing;
 using System.Linq;
 using Robust.Client.Graphics;
 using Robust.Client.Placement;
+using Robust.Client.Placement.Modes;
 using Robust.Client.ResourceManagement;
 using Robust.Client.UserInterface.Controls;
 using Robust.Client.UserInterface.CustomControls;
@@ -28,19 +30,23 @@ public sealed class TileSpawningUIController : UIController
     private readonly List<ITileDefinition> _shownTiles = new();
     private bool _clearingTileSelections;
     private bool _eraseTile;
+    private bool _mirrorableTile; // Tracks if the chosen tile even can be mirrored.
+    private bool _mirroredTile;
 
     public override void Initialize()
     {
         DebugTools.Assert(_init == false);
         _init = true;
         _placement.PlacementChanged += ClearTileSelection;
+        _placement.DirectionChanged += OnDirectionChanged;
+        _placement.MirroredChanged += OnMirroredChanged;
     }
 
     private void StartTilePlacement(int tileType)
     {
         var newObjInfo = new PlacementInformation
         {
-            PlacementOption = "AlignTileAny",
+            PlacementOption = nameof(AlignTileAny),
             TileType = tileType,
             Range = 400,
             IsTile = true
@@ -67,6 +73,17 @@ public sealed class TileSpawningUIController : UIController
         args.Button.Pressed = args.Pressed;
     }
 
+    private void OnTileMirroredToggled(ButtonToggledEventArgs args)
+    {
+        if (_window == null || _window.Disposed)
+            return;
+
+        _placement.Mirrored = args.Pressed;
+        _mirroredTile = _placement.Mirrored;
+
+        args.Button.Pressed = args.Pressed;
+    }
+
     public void ToggleWindow()
     {
         EnsureWindow();
@@ -78,6 +95,9 @@ public sealed class TileSpawningUIController : UIController
         else
         {
             _window.Open();
+            UpdateEntityDirectionLabel();
+            UpdateMirroredButton();
+            _window.SearchBar.GrabKeyboardFocus();
         }
     }
 
@@ -93,6 +113,10 @@ public sealed class TileSpawningUIController : UIController
         _window.TileList.OnItemDeselected += OnTileItemDeselected;
         _window.EraseButton.Pressed = _eraseTile;
         _window.EraseButton.OnToggled += OnTileEraseToggled;
+        _window.MirroredButton.Disabled = !_mirrorableTile;
+        _window.RotationLabel.FontColorOverride = _mirrorableTile ? Color.White : Color.Gray;
+        _window.MirroredButton.Pressed = _mirroredTile;
+        _window.MirroredButton.OnToggled += OnTileMirroredToggled;
         BuildTileList();
     }
 
@@ -110,6 +134,7 @@ public sealed class TileSpawningUIController : UIController
         _window.TileList.ClearSelected();
         _clearingTileSelections = false;
         _window.EraseButton.Pressed = false;
+        _window.MirroredButton.Pressed = _placement.Mirrored;
     }
 
     private void OnTileClearPressed(ButtonEventArgs args)
@@ -137,6 +162,7 @@ public sealed class TileSpawningUIController : UIController
     {
         var definition = _shownTiles[args.ItemIndex];
         StartTilePlacement(definition.TileId);
+        UpdateMirroredButton();
     }
 
     private void OnTileItemDeselected(ItemList.ItemListDeselectedEventArgs args)
@@ -149,6 +175,41 @@ public sealed class TileSpawningUIController : UIController
         _placement.Clear();
     }
 
+    private void OnDirectionChanged(object? sender, EventArgs e)
+    {
+        UpdateEntityDirectionLabel();
+    }
+
+    private void UpdateEntityDirectionLabel()
+    {
+        if (_window == null || _window.Disposed)
+            return;
+
+        _window.RotationLabel.Text = _placement.Direction.ToString();
+    }
+
+    private void OnMirroredChanged(object? sender, EventArgs e)
+    {
+        UpdateMirroredButton();
+    }
+
+    private void UpdateMirroredButton()
+    {
+        if (_window == null || _window.Disposed)
+            return;
+
+        if (_placement.CurrentPermission != null && _placement.CurrentPermission.IsTile)
+        {
+            var allowed = _tiles[_placement.CurrentPermission.TileType].AllowRotationMirror;
+            _mirrorableTile = allowed;
+            _window.MirroredButton.Disabled = !_mirrorableTile;
+            _window.RotationLabel.FontColorOverride = _mirrorableTile ? Color.White : Color.Gray;
+        }
+
+        _mirroredTile = _placement.Mirrored;
+        _window.MirroredButton.Pressed = _mirroredTile;
+    }
+
     private void BuildTileList(string? searchStr = null)
     {
         if (_window == null || _window.Disposed) return;

Robust.Client/UserInterface/Controllers/UIController.cs

@@ -1,6 +1,9 @@
 using System.Diagnostics.CodeAnalysis;
+using System.Globalization;
+using System.Linq;
 using Robust.Shared.GameObjects;
 using Robust.Shared.IoC;
+using Robust.Shared.Log;
 using Robust.Shared.Timing;
 
 namespace Robust.Client.UserInterface.Controllers;
@@ -11,11 +14,14 @@ namespace Robust.Client.UserInterface.Controllers;
 ///     and <see cref="UISystemDependencyAttribute"/> to depend on <see cref="EntitySystem"/>s, which will be automatically
 ///     injected once they are created.
 /// </summary>
-public abstract partial class UIController
+public abstract partial class UIController : IPostInjectInit
 {
     [Dependency] protected readonly IUserInterfaceManager UIManager = default!;
     [Dependency] protected readonly IEntitySystemManager EntitySystemManager = default!;
     [Dependency] protected readonly IEntityManager EntityManager = default!;
+    [Dependency] protected readonly ILogManager LogManager = default!;
+
+    public ISawmill Log { get; protected set; } = default!;
 
     public virtual void Initialize()
     {
@@ -24,4 +30,39 @@ public abstract partial class UIController
     public virtual void FrameUpdate(FrameEventArgs args)
     {
     }
+
+    protected virtual string SawmillName
+    {
+        get
+        {
+            var name = GetType().Name;
+
+            // Strip trailing "UIController"
+            if (name.EndsWith("UIController"))
+                name = name.Substring(0, name.Length - "UIController".Length);
+
+            // Convert CamelCase to snake_case
+            // Ignore if all uppercase, assume acronym (e.g. NPC or HTN)
+            if (name.All(char.IsUpper))
+            {
+                name = name.ToLower(CultureInfo.InvariantCulture);
+            }
+            else
+            {
+                name = string.Concat(name.Select(x => char.IsUpper(x) ? $"_{char.ToLower(x)}" : x.ToString()));
+                name = name.Trim('_');
+            }
+
+            return $"ui.{name}";
+        }
+    }
+
+    public void PostInject()
+    {
+        Log = LogManager.GetSawmill(SawmillName);
+
+#if !DEBUG
+        Log.Level = LogLevel.Info;
+#endif
+    }
 }

Robust.Client/UserInterface/Controls/ItemList.cs

@@ -741,7 +741,7 @@ namespace Robust.Client.UserInterface.Controls
                 get => _selected;
                 set
                 {
-                    if (!Selectable) return;
+                    if (!Selectable || _selected == value) return;
                     _selected = value;
                     if(_selected) OnSelected?.Invoke(this);
                     else OnDeselected?.Invoke(this);

Robust.Client/UserInterface/Controls/OutputPanel.cs

@@ -95,6 +95,12 @@ namespace Robust.Client.UserInterface.Controls
         public void Clear()
         {
             _firstLine = true;
+
+            foreach (var entry in _entries)
+            {
+                entry.RemoveControls();
+            }
+
             _entries.Clear();
             _totalContentHeight = 0;
             _scrollBar.MaxValue = Math.Max(_scrollBar.Page, _totalContentHeight);
@@ -104,6 +110,7 @@ namespace Robust.Client.UserInterface.Controls
         public void RemoveEntry(Index index)
         {
             var entry = _entries[index];
+            entry.RemoveControls();
             _entries.RemoveAt(index.GetOffset(_entries.Count));
 
             var font = _getFont();
@@ -189,6 +196,9 @@ namespace Robust.Client.UserInterface.Controls
                 if (entryOffset > contentBox.Height)
                 {
                     entry.HideControls();
+
+                    // We know that every subsequent entry will also fail the test, but we also need to
+                    // hide all the controls, so we cannot simply break out of the loop
                     continue;
                 }
 

Robust.Client/UserInterface/Controls/ProgressBar.cs

@@ -14,6 +14,27 @@ namespace Robust.Client.UserInterface.Controls
         private StyleBox? _backgroundStyleBoxOverride;
         private StyleBox? _foregroundStyleBoxOverride;
 
+        private bool _vertical;
+
+        /// <summary>
+        /// Whether the progress bar is oriented vertically.
+        /// </summary>
+        /// <remarks>
+        /// A vertical progress bar fills from bottom to top.
+        /// </remarks>
+        public bool Vertical
+        {
+            get => _vertical;
+            set
+            {
+                if (_vertical != value)
+                {
+                    _vertical = value;
+                    InvalidateMeasure();
+                }
+            }
+        }
+
         public StyleBox? BackgroundStyleBoxOverride
         {
             get => _backgroundStyleBoxOverride;
@@ -70,11 +91,23 @@ namespace Robust.Client.UserInterface.Controls
             {
                 return;
             }
-            var minSize = fg.MinimumSize;
-            var size = PixelWidth * GetAsRatio() - minSize.X;
-            if (size > 0)
+
+            if (_vertical)
             {
-                fg.Draw(handle, UIBox2.FromDimensions(0, 0, minSize.X + size, PixelHeight), UIScale);
+                var size = PixelHeight * GetAsRatio();
+                if (size > 0)
+                {
+                    fg.Draw(handle, UIBox2.FromDimensions(0, PixelHeight - size, PixelWidth, size), UIScale);
+                }
+            }
+            else
+            {
+                var minSize = fg.MinimumSize;
+                var size = PixelWidth * GetAsRatio() - minSize.X;
+                if (size > 0)
+                {
+                    fg.Draw(handle, UIBox2.FromDimensions(0, 0, minSize.X + size, PixelHeight), UIScale);
+                }
             }
         }
 

Robust.Client/UserInterface/Controls/RichTextLabel.cs

@@ -1,4 +1,6 @@
 using System;
+using System.Collections.Generic;
+using System.Linq;
 using System.Numerics;
 using JetBrains.Annotations;
 using Robust.Client.Graphics;
@@ -15,8 +17,7 @@ namespace Robust.Client.UserInterface.Controls
     {
         [Dependency] private readonly MarkupTagManager _tagManager = default!;
 
-        private FormattedMessage? _message;
-        private RichTextEntry _entry;
+        private RichTextEntry? _entry;
         private float _lineHeightScale = 1;
         private bool _lineHeightOverride;
 
@@ -40,19 +41,26 @@ namespace Robust.Client.UserInterface.Controls
 
         public string? Text
         {
-            get => _message?.ToMarkup();
+            get => _entry?.Message.ToMarkup();
             set
             {
                 if (value == null)
-                {
-                    _message?.Clear();
-                    return;
-                }
-
-                SetMessage(FormattedMessage.FromMarkupPermissive(value));
+                    Clear();
+                else
+                    SetMessage(FormattedMessage.FromMarkupPermissive(value));
             }
         }
 
+        public void Clear()
+        {
+            _entry?.RemoveControls();
+            _entry = null;
+            InvalidateMeasure();
+        }
+
+        public IEnumerable<Control> Controls => _entry?.Controls?.Values ?? Enumerable.Empty<Control>();
+        public IReadOnlyList<MarkupNode> Nodes => _entry?.Message.Nodes ?? Array.Empty<MarkupNode>();
+
         public RichTextLabel()
         {
             IoCManager.InjectDependencies(this);
@@ -61,8 +69,8 @@ namespace Robust.Client.UserInterface.Controls
 
         public void SetMessage(FormattedMessage message, Type[]? tagsAllowed = null, Color? defaultColor = null)
         {
-            _message = message;
-            _entry = new RichTextEntry(_message, this, _tagManager, tagsAllowed, defaultColor);
+            _entry?.RemoveControls();
+            _entry = new RichTextEntry(message, this, _tagManager, tagsAllowed, defaultColor);
             InvalidateMeasure();
         }
 
@@ -73,31 +81,31 @@ namespace Robust.Client.UserInterface.Controls
             SetMessage(msg, tagsAllowed, defaultColor);
         }
 
-        public string? GetMessage() => _message?.ToMarkup();
+        public string? GetMessage() => _entry?.Message.ToMarkup();
+
+        /// <summary>
+        /// Returns a copy of the currently used formatted message.
+        /// </summary>
+        public FormattedMessage? GetFormattedMessage() => _entry == null ? null : new FormattedMessage(_entry.Value.Message);
 
         protected override Vector2 MeasureOverride(Vector2 availableSize)
         {
-            if (_message == null)
-            {
+            if (_entry == null)
                 return Vector2.Zero;
-            }
 
             var font = _getFont();
-            _entry.Update(_tagManager, font, availableSize.X * UIScale, UIScale, LineHeightScale);
 
-            return new Vector2(_entry.Width / UIScale, _entry.Height / UIScale);
+            // _entry is nullable struct.
+            // cannot just call _entry.Value.Update() as that doesn't actually update _entry.
+            _entry = _entry.Value.Update(_tagManager, font, availableSize.X * UIScale, UIScale, LineHeightScale);
+
+            return new Vector2(_entry.Value.Width / UIScale, _entry.Value.Height / UIScale);
         }
 
         protected internal override void Draw(DrawingHandleScreen handle)
         {
             base.Draw(handle);
-
-            if (_message == null)
-            {
-                return;
-            }
-
-            _entry.Draw(_tagManager, handle, _getFont(), SizeBox, 0, new MarkupDrawingContext(), UIScale, LineHeightScale);
+            _entry?.Draw(_tagManager, handle, _getFont(), SizeBox, 0, new MarkupDrawingContext(), UIScale, LineHeightScale);
         }
 
         [Pure]

Robust.Client/UserInterface/CustomControls/TileSpawnWindow.xaml

@@ -10,7 +10,9 @@
         </BoxContainer>
         <ItemList Name="TileList" Access="Public" VerticalExpand="True"/>
         <BoxContainer Orientation="Horizontal">
+            <Button Name="MirroredButton" Access="Public" ToggleMode="True" Text="{Loc tile-spawn-window-mirror-button-text}"/>
             <Button Name="EraseButton" Access="Public" ToggleMode="True" Text="{Loc window-erase-button-text}"/>
         </BoxContainer>
+        <Label Name="RotationLabel" Access="Public"/>
     </BoxContainer>
 </TileSpawnWindow>

Robust.Client/UserInterface/DevWindow/DevWindow.xaml

@@ -5,5 +5,6 @@
         <DebugConsole Name="DebugConsole" />
         <DevWindowTabUI Name="UI" />
         <DevWindowTabPerf Name="Perf" />
+        <DevWindowTabTextures Name="Textures" />
     </TabContainer>
 </Control>

Robust.Client/UserInterface/DevWindow/DevWindow.xaml.cs

@@ -8,6 +8,7 @@ using Robust.Client.UserInterface.Stylesheets;
 using Robust.Client.UserInterface.XAML;
 using Robust.Shared.Console;
 using Robust.Shared.IoC;
+using Robust.Shared.Localization;
 
 namespace Robust.Client.UserInterface
 {
@@ -26,6 +27,7 @@ namespace Robust.Client.UserInterface
             TabContainer.SetTabTitle(DebugConsole, "Debug Console");
             TabContainer.SetTabTitle(UI, "User Interface");
             TabContainer.SetTabTitle(Perf, "Profiling");
+            TabContainer.SetTabTitle(Textures, Loc.GetString("dev-window-tab-textures-title"));
 
             Stylesheet =
                 new DefaultStylesheet(IoCManager.Resolve<IResourceCache>(), IoCManager.Resolve<IUserInterfaceManager>()).Stylesheet;

Robust.Client/UserInterface/DevWindow/DevWindowTabTextures.xaml

@@ -0,0 +1,26 @@
+<Control xmlns="https://spacestation14.io"
+         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+         x:Class="Robust.Client.UserInterface.DevWindowTabTextures">
+    <SplitContainer Orientation="Horizontal">
+        <!-- Left pane: list of textures -->
+        <BoxContainer Orientation="Vertical" MinWidth="200">
+            <Button Name="ReloadButton" Text="{Loc 'dev-window-tab-textures-reload'}" />
+            <LineEdit Name="SearchBar" PlaceHolder="{Loc 'dev-window-tab-textures-filter'}" />
+
+            <ScrollContainer HScrollEnabled="False" VerticalExpand="True">
+                <BoxContainer Name="TextureList" Orientation="Vertical" />
+            </ScrollContainer>
+
+            <Label Name="SummaryLabel" Margin="4" />
+        </BoxContainer>
+
+        <!-- Right pane: show the selected texture info -->
+        <Control MinWidth="400">
+            <BoxContainer Orientation="Vertical">
+                <TextureRect Name="SelectedTextureDisplay" VerticalExpand="True" CanShrink="True"
+                             Stretch="KeepAspectCentered" />
+                <Label Name="SelectedTextureInfo" />
+            </BoxContainer>
+        </Control>
+    </SplitContainer>
+</Control>

Robust.Client/UserInterface/DevWindow/DevWindowTabTextures.xaml.cs

@@ -0,0 +1,136 @@
+using System;
+using System.Linq;
+using Robust.Client.AutoGenerated;
+using Robust.Client.Graphics;
+using Robust.Client.Graphics.Clyde;
+using Robust.Client.UserInterface.Controls;
+using Robust.Client.UserInterface.XAML;
+using Robust.Shared.IoC;
+using Robust.Shared.Localization;
+using Robust.Shared.Utility;
+
+namespace Robust.Client.UserInterface;
+
+/// <summary>
+/// Shows all loaded textures in the game.
+/// </summary>
+[GenerateTypedNameReferences]
+internal sealed partial class DevWindowTabTextures : Control
+{
+    [Dependency] private readonly IClydeInternal _clyde = null!;
+    [Dependency] private readonly ILocalizationManager _loc = null!;
+
+    public DevWindowTabTextures()
+    {
+        RobustXamlLoader.Load(this);
+        IoCManager.InjectDependencies(this);
+
+        ReloadButton.OnPressed += _ => Reload();
+        SearchBar.OnTextChanged += _ => Reload();
+    }
+
+    protected override void VisibilityChanged(bool newVisible)
+    {
+        if (newVisible)
+        {
+            Reload();
+        }
+        else
+        {
+            // Clear to release memory when tab not visible.
+            Clear();
+        }
+    }
+
+    private void Clear()
+    {
+        TextureList.RemoveAllChildren();
+    }
+
+    private void Reload()
+    {
+        Clear();
+
+        var total = 0L;
+
+        foreach (var (clydeTexture, loadedTexture) in _clyde.GetLoadedTextures()
+                     .OrderByDescending(tup => tup.Item2.MemoryPressure))
+        {
+            if (!string.IsNullOrWhiteSpace(SearchBar.Text))
+            {
+                if (loadedTexture.Name is not { } name)
+                    continue;
+
+                if (!name.Contains(SearchBar.Text, StringComparison.CurrentCultureIgnoreCase))
+                    continue;
+            }
+
+            if (loadedTexture.MemoryPressure == 0)
+            {
+                // Bad hack to avoid showing render targets lol.
+                continue;
+            }
+
+            var button = new ContainerButton
+            {
+                Children = { new TextureEntry(loadedTexture, clydeTexture) }
+            };
+            button.OnPressed += _ => SelectTexture(loadedTexture, clydeTexture);
+
+            TextureList.AddChild(button);
+
+            total += loadedTexture.MemoryPressure;
+        }
+
+        SummaryLabel.Text =
+            _loc.GetString("dev-window-tab-textures-summary", ("bytes", ByteHelpers.FormatBytes(total)));
+    }
+
+    private void SelectTexture(Clyde.LoadedTexture loaded, Clyde.ClydeTexture texture)
+    {
+        SelectedTextureDisplay.Texture = texture;
+        SelectedTextureInfo.Text = _loc.GetString("dev-window-tab-textures-info",
+            ("width", loaded.Width),
+            ("height", loaded.Height),
+            ("pixelType", loaded.TexturePixelType),
+            ("srgb", loaded.IsSrgb),
+            ("name", loaded.Name ?? ""),
+            ("bytes", ByteHelpers.FormatBytes(loaded.MemoryPressure)));
+    }
+
+    private sealed class TextureEntry : Control
+    {
+        public TextureEntry(Clyde.LoadedTexture loaded, Clyde.ClydeTexture texture)
+        {
+            SetHeight = 64;
+
+            var bytes = ByteHelpers.FormatBytes(loaded.MemoryPressure);
+
+            var label = loaded.Name == null
+                ? $"{texture.TextureId} ({bytes})"
+                : $"{loaded.Name}\n{texture.TextureId} ({bytes})";
+
+            AddChild(new BoxContainer
+            {
+                Orientation = BoxContainer.LayoutOrientation.Horizontal,
+                Children =
+                {
+                    new TextureRect
+                    {
+                        SetWidth = 64,
+                        Texture = texture,
+                        CanShrink = true,
+                        RectClipContent = true,
+                        Stretch = TextureRect.StretchMode.Scale
+                    },
+                    new Label
+                    {
+                        Text = label,
+                        ClipText = true,
+                        HorizontalExpand = true
+                    }
+                }
+            });
+        }
+    }
+}

Robust.Client/UserInterface/DummyFileDialogManager.cs

@@ -8,12 +8,19 @@ namespace Robust.Client.UserInterface
     /// </summary>
     internal sealed class DummyFileDialogManager : IFileDialogManager
     {
-        public Task<Stream?> OpenFile(FileDialogFilters? filters = null)
+        public Task<Stream?> OpenFile(
+            FileDialogFilters? filters = null,
+            FileAccess access = FileAccess.ReadWrite,
+            FileShare? share = null)
         {
             return Task.FromResult<Stream?>(null);
         }
 
-        public Task<(Stream fileStream, bool alreadyExisted)?> SaveFile(FileDialogFilters? filters = null, bool truncate = true)
+        public Task<(Stream fileStream, bool alreadyExisted)?> SaveFile(
+            FileDialogFilters? filters = null,
+            bool truncate = true,
+            FileAccess access = FileAccess.ReadWrite,
+            FileShare share = FileShare.None)
         {
             return Task.FromResult<(Stream fileStream, bool alreadyExisted)?>(null);
         }

Robust.Client/UserInterface/FileDialogManager.cs

@@ -7,9 +7,7 @@ using System.Runtime.InteropServices;
 using System.Text;
 using System.Threading.Tasks;
 using Robust.Client.Graphics;
-using Robust.Shared;
 using Robust.Shared.Console;
-using Robust.Shared.Asynchronous;
 using Robust.Shared.IoC;
 using Robust.Shared.Log;
 using Robust.Shared.Utility;
@@ -30,18 +28,28 @@ namespace Robust.Client.UserInterface
         private bool _kDialogAvailable;
         private bool _checkedKDialogAvailable;
 
-        public async Task<Stream?> OpenFile(FileDialogFilters? filters = null)
+        public async Task<Stream?> OpenFile(
+            FileDialogFilters? filters = null,
+            FileAccess access = FileAccess.ReadWrite,
+            FileShare? share = null)
         {
+            if ((access & FileAccess.ReadWrite) != access)
+                throw new ArgumentException("Invalid file access specified");
+
+            var realShare = share ?? (access == FileAccess.Read ? FileShare.Read : FileShare.None);
+            if ((realShare & (FileShare.ReadWrite | FileShare.Delete)) != realShare)
+                throw new ArgumentException("Invalid file share specified");
+
+            string? name;
             if (_clyde.FileDialogImpl is { } clydeImpl)
-                return await clydeImpl.OpenFile(filters);
+                name = await clydeImpl.OpenFile(filters);
+            else
+                name = await GetOpenFileName(filters);
 
-            var name = await GetOpenFileName(filters);
             if (name == null)
-            {
                 return null;
-            }
 
-            return File.Open(name, FileMode.Open);
+            return File.Open(name, FileMode.Open, access, realShare);
         }
 
         private async Task<string?> GetOpenFileName(FileDialogFilters? filters)
@@ -54,24 +62,34 @@ namespace Robust.Client.UserInterface
             return await OpenFileNfd(filters);
         }
 
-        public async Task<(Stream, bool)?> SaveFile(FileDialogFilters? filters, bool truncate = true)
+        public async Task<(Stream, bool)?> SaveFile(
+            FileDialogFilters? filters,
+            bool truncate = true,
+            FileAccess access = FileAccess.ReadWrite,
+            FileShare share = FileShare.None)
         {
-            if (_clyde.FileDialogImpl is { } clydeImpl)
-                return await clydeImpl.SaveFile(filters);
+            if ((access & FileAccess.ReadWrite) != access)
+                throw new ArgumentException("Invalid file access specified");
+
+            if ((share & (FileShare.ReadWrite | FileShare.Delete)) != share)
+                throw new ArgumentException("Invalid file share specified");
+
+            string? name;
+            if (_clyde.FileDialogImpl is { } clydeImpl)
+                name = await clydeImpl.SaveFile(filters);
+            else
+                name = await GetSaveFileName(filters);
 
-            var name = await GetSaveFileName(filters);
             if (name == null)
-            {
                 return null;
-            }
 
             try
             {
-                return (File.Open(name, truncate ? FileMode.Truncate : FileMode.Open), true);
+                return (File.Open(name, truncate ? FileMode.Truncate : FileMode.Open, access, share), true);
             }
             catch (FileNotFoundException)
             {
-                return (File.Open(name, FileMode.Create), false);
+                return (File.Open(name, FileMode.Create, access, share), false);
             }
         }
 

Robust.Client/UserInterface/IFileDialogManager.cs

@@ -1,5 +1,6 @@
 using System.IO;
 using System.Threading.Tasks;
+using Robust.Client.Graphics;
 
 namespace Robust.Client.UserInterface
 {
@@ -19,7 +20,17 @@ namespace Robust.Client.UserInterface
         /// The file stream for the file the user opened.
         /// <see langword="null" /> if the user cancelled the action.
         /// </returns>
-        Task<Stream?> OpenFile(FileDialogFilters? filters = null);
+        /// <param name="filters">Filters for file types that the user can select.</param>
+        /// <param name="access">What access is desired from the file operation.</param>
+        /// <param name="share">
+        /// What sharing mode is desired from the file operation.
+        /// If null is provided and <paramref name="access"/> is <see cref="FileAccess.Read"/>,
+        /// <see cref="FileShare.Read"/> is selected, otherwise <see cref="FileShare.None"/>.
+        /// </param>
+        Task<Stream?> OpenFile(
+            FileDialogFilters? filters = null,
+            FileAccess access = FileAccess.ReadWrite,
+            FileShare? share = null);
 
         /// <summary>
         ///     Open a file dialog used for saving a single file.
@@ -29,6 +40,21 @@ namespace Robust.Client.UserInterface
         /// Null if the user cancelled the action.
         /// </returns>
         /// <param name="truncate">Should we truncate an existing file to 0-size then write or append.</param>
-        Task<(Stream fileStream, bool alreadyExisted)?> SaveFile(FileDialogFilters? filters = null, bool truncate = true);
+        /// <param name="access">What access is desired from the file operation.</param>
+        /// <param name="share">Sharing mode for the opened file.</param>
+        Task<(Stream fileStream, bool alreadyExisted)?> SaveFile(
+            FileDialogFilters? filters = null,
+            bool truncate = true,
+            FileAccess access = FileAccess.ReadWrite,
+            FileShare share = FileShare.None);
+    }
+
+    /// <summary>
+    /// Internal implementation interface used to connect <see cref="FileDialogManager"/> and <see cref="IClydeInternal"/>.
+    /// </summary>
+    internal interface IFileDialogManagerImplementation
+    {
+        Task<string?> OpenFile(FileDialogFilters? filters);
+        Task<string?> SaveFile(FileDialogFilters? filters);
     }
 }

Robust.Client/UserInterface/RichText/BoldItalicTag.cs

@@ -5,7 +5,7 @@ using Robust.Shared.Utility;
 
 namespace Robust.Client.UserInterface.RichText;
 
-public sealed class BoldItalicTag : IMarkupTag
+public sealed class BoldItalicTag : IMarkupTagHandler
 {
     public const string BoldItalicFont = "DefaultBoldItalic";
 

Robust.Client/UserInterface/RichText/BoldTag.cs

@@ -6,7 +6,7 @@ using Robust.Shared.Utility;
 
 namespace Robust.Client.UserInterface.RichText;
 
-public sealed class BoldTag : IMarkupTag
+public sealed class BoldTag : IMarkupTagHandler
 {
     public const string BoldFont = "DefaultBold";
 

Robust.Client/UserInterface/RichText/BulletTag.cs

@@ -2,7 +2,7 @@ using Robust.Shared.Utility;
 
 namespace Robust.Client.UserInterface.RichText;
 
-public sealed class BulletTag : IMarkupTag
+public sealed class BulletTag : IMarkupTagHandler
 {
     public string Name => "bullet";
 

Robust.Client/UserInterface/RichText/ColorTag.cs

@@ -6,7 +6,7 @@ namespace Robust.Client.UserInterface.RichText;
 /// <summary>
 /// Colors the text inside its opening and closing nodes
 /// </summary>
-public sealed class ColorTag : IMarkupTag
+public sealed class ColorTag : IMarkupTagHandler
 {
     public static readonly Color DefaultColor = new(200, 200, 200);
 

Robust.Client/UserInterface/RichText/CommandLinkTag.cs

@@ -8,14 +8,14 @@ using Robust.Shared.Utility;
 
 namespace Robust.Client.UserInterface.RichText;
 
-public sealed class CommandLinkTag : IMarkupTag
+public sealed class CommandLinkTag : IMarkupTagHandler
 {
     [Dependency] private readonly IClientConsoleHost _clientConsoleHost = default!;
 
     public string Name => "cmdlink";
 
     /// <inheritdoc/>
-    public bool TryGetControl(MarkupNode node, [NotNullWhen(true)] out Control? control)
+    public bool TryCreateControl(MarkupNode node, [NotNullWhen(true)] out Control? control)
     {
         if (!node.Value.TryGetString(out var text)
             || !node.Attributes.TryGetValue("command", out var commandParameter)

Robust.Client/UserInterface/RichText/FontTag.cs

@@ -11,7 +11,7 @@ namespace Robust.Client.UserInterface.RichText;
 /// Applies the font provided as the tags parameter to the markup drawing context.
 /// Definitely not save for user supplied markup
 /// </summary>
-public sealed class FontTag : IMarkupTag
+public sealed class FontTag : IMarkupTagHandler
 {
     public const string DefaultFont = "Default";
     public const int DefaultSize = 12;

Robust.Client/UserInterface/RichText/HeadingTag.cs

@@ -6,7 +6,7 @@ using Robust.Shared.Utility;
 
 namespace Robust.Client.UserInterface.RichText;
 
-public sealed class HeadingTag : IMarkupTag
+public sealed class HeadingTag : IMarkupTagHandler
 {
     [Dependency] private readonly IResourceCache _resourceCache = default!;
     [Dependency] private readonly IPrototypeManager _prototypeManager = default!;

Robust.Client/UserInterface/RichText/IMarkupTag.cs

@@ -1,9 +1,16 @@
+using System;
 using System.Diagnostics.CodeAnalysis;
 using Robust.Shared.Utility;
 
 namespace Robust.Client.UserInterface.RichText;
 
-public interface IMarkupTag
+/// <summary>
+/// Classes that implement this interface will be instantiated by <see cref="MarkupTagManager"/> and used to handle
+/// the parsing and behaviour of markup tags. Note that each class is only ever instantiated once by the tag manager,
+/// and wil be used to handle all tags of that kind, and thus should not contain state information relevant to a
+/// specific tag.
+/// </summary>
+public interface IMarkupTagHandler
 {
     /// <summary>
     /// The string used as the tags name when writing rich text
@@ -54,17 +61,32 @@ public interface IMarkupTag
     }
 
     /// <summary>
-    /// Called inside the constructor of <see cref="RichTextEntry"/> to
-    /// supply a control that gets rendered inline before this tags children<br/>
-    /// Text continues to the right of the control until the next line and then continues bellow it
+    /// Called inside the constructor of <see cref="RichTextEntry"/> to supply a control that gets rendered inline
+    /// before this tags children. The returned control must be new instance to avoid issues with shallow cloning
+    /// <see cref="FormattedMessage"/> nodes. Text continues to the right of the control until the next line and
+    /// then continues bellow it.
     /// </summary>
     /// <param name="node">The markup node containing the parameter and attributes</param>
     /// <param name="control">A UI control for placing in line with this tags children</param>
     /// <returns>true if this tag supplies a control</returns>
+    public bool TryCreateControl(MarkupNode node, [NotNullWhen(true)] out Control? control)
+    {
+        control = null;
+        return false;
+    }
+}
+
+[Obsolete("Use IMarkupTagHandler")]
+public interface IMarkupTag : IMarkupTagHandler
+{
+    bool IMarkupTagHandler.TryCreateControl(MarkupNode node, [NotNullWhen(true)] out Control? control)
+    {
+        return TryGetControl(node, out control);
+    }
+
     public bool TryGetControl(MarkupNode node, [NotNullWhen(true)] out Control? control)
     {
         control = null;
         return false;
     }
-
 }

Robust.Client/UserInterface/RichText/ItalicTag.cs

@@ -6,7 +6,7 @@ using Robust.Shared.Utility;
 
 namespace Robust.Client.UserInterface.RichText;
 
-public sealed class ItalicTag : IMarkupTag
+public sealed class ItalicTag : IMarkupTagHandler
 {
     public const string ItalicFont = "DefaultItalic";
 

Robust.Client/UserInterface/RichText/MarkupTagManager.cs

@@ -16,7 +16,7 @@ public sealed class MarkupTagManager
     /// <summary>
     /// Tags defined in engine need to be instantiated here because of sandboxing
     /// </summary>
-    private readonly Dictionary<string, IMarkupTag> _markupTagTypes = new IMarkupTag[] {
+    private readonly Dictionary<string, IMarkupTagHandler> _markupTagTypes = new IMarkupTagHandler[] {
         new BoldItalicTag(),
         new BoldTag(),
         new BulletTag(),
@@ -44,13 +44,13 @@ public sealed class MarkupTagManager
 
     public void Initialize()
     {
-        foreach (var type in _reflectionManager.GetAllChildren<IMarkupTag>())
+        foreach (var type in _reflectionManager.GetAllChildren<IMarkupTagHandler>())
         {
             //Prevent tags defined inside engine from being instantiated
             if (_engineTypes.Contains(type))
                 continue;
 
-            var instance = (IMarkupTag)_sandboxHelper.CreateInstance(type);
+            var instance = (IMarkupTagHandler)_sandboxHelper.CreateInstance(type);
             _markupTagTypes[instance.Name.ToLower()] = instance;
         }
 
@@ -60,22 +60,48 @@ public sealed class MarkupTagManager
         }
     }
 
+    [Obsolete("Use GetMarkupTagHandler")]
     public IMarkupTag? GetMarkupTag(string name)
+    {
+        return _markupTagTypes.GetValueOrDefault(name) as IMarkupTag;
+    }
+
+    public IMarkupTagHandler? GetMarkupTagHandler(string name)
     {
         return _markupTagTypes.GetValueOrDefault(name);
     }
 
-    public bool TryGetMarkupTag(string name, Type[]? tagsAllowed, [NotNullWhen(true)] out IMarkupTag? tag)
+    /// <summary>
+    /// Attempt to get the tag handler with the corresponding name.
+    /// </summary>
+    /// <param name="name">The name of the tag, as specified by <see cref="IMarkupTag.Name"/></param>
+    /// <param name="tagsAllowed">List of allowed tag types. If null, all types are allowed.</param>
+    /// <param name="handler">The instance responsible for handling tags of this type.</param>
+    /// <returns></returns>
+    public bool TryGetMarkupTagHandler(string name, Type[]? tagsAllowed, [NotNullWhen(true)] out IMarkupTagHandler? handler)
     {
         if (_markupTagTypes.TryGetValue(name, out var markupTag)
             // Using a whitelist prevents new tags from sneaking in.
             && (tagsAllowed == null || Array.IndexOf(tagsAllowed, markupTag.GetType()) != -1))
         {
-            tag = markupTag;
+            handler = markupTag;
             return true;
         }
 
-        tag = null;
+        handler = null;
         return false;
     }
+
+    [Obsolete("Use TryGetMarkupTagHandler")]
+    public bool TryGetMarkupTag(string name, Type[]? tagsAllowed, [NotNullWhen(true)] out IMarkupTag? tag)
+    {
+        if (!TryGetMarkupTagHandler(name, tagsAllowed, out var handler) || handler is not IMarkupTag cast)
+        {
+            tag = null;
+            return false;
+        }
+
+        tag = cast;
+        return true;
+    }
 }

Robust.Client/UserInterface/RichTextEntry.cs

@@ -13,6 +13,9 @@ namespace Robust.Client.UserInterface
 {
     /// <summary>
     ///     Used by <see cref="OutputPanel"/> and <see cref="RichTextLabel"/> to handle rich text layout.
+    ///     Note that if this text is ever removed or modified without removing the owning control,
+    ///     then <see cref="RemoveControls"/> should be called to ensure that any controls that were added by this
+    ///     entry are also removed.
     /// </summary>
     internal struct RichTextEntry
     {
@@ -36,7 +39,7 @@ namespace Robust.Client.UserInterface
         /// </summary>
         public ValueList<int> LineBreaks;
 
-        private readonly Dictionary<int, Control>? _tagControls;
+        public readonly Dictionary<int, Control>? Controls;
 
         public RichTextEntry(FormattedMessage message, Control parent, MarkupTagManager tagManager, Type[]? tagsAllowed = null, Color? defaultColor = null)
         {
@@ -56,15 +59,35 @@ namespace Robust.Client.UserInterface
                 if (node.Name == null)
                     continue;
 
-                if (!tagManager.TryGetMarkupTag(node.Name, _tagsAllowed, out var tag) || !tag.TryGetControl(node, out var control))
+                if (!tagManager.TryGetMarkupTagHandler(node.Name, _tagsAllowed, out var handler) || !handler.TryCreateControl(node, out var control))
                     continue;
 
+                // Markup tag handler instances are shared across controls. We need to ensure that the hanlder doesn't
+                // store state information and return the same control for each rich text entry.
+                DebugTools.Assert(handler.TryCreateControl(node, out var other) && other != control);
+
                 parent.Children.Add(control);
                 tagControls ??= new Dictionary<int, Control>();
                 tagControls.Add(nodeIndex, control);
             }
 
-            _tagControls = tagControls;
+            Controls = tagControls;
+        }
+
+        // TODO RICH TEXT
+        // Somehow ensure that this **has** to be called when removing rich text from some control.
+        /// <summary>
+        /// Remove all owned controls from their parents.
+        /// </summary>
+        public readonly void RemoveControls()
+        {
+            if (Controls == null)
+                return;
+
+            foreach (var ctrl in Controls.Values)
+            {
+                ctrl.Orphan();
+            }
         }
 
         /// <summary>
@@ -74,7 +97,7 @@ namespace Robust.Client.UserInterface
         /// <param name="maxSizeX">The maximum horizontal size of the container of this entry.</param>
         /// <param name="uiScale"></param>
         /// <param name="lineHeightScale"></param>
-        public void Update(MarkupTagManager tagManager, Font defaultFont, float maxSizeX, float uiScale, float lineHeightScale = 1)
+        public RichTextEntry Update(MarkupTagManager tagManager, Font defaultFont, float maxSizeX, float uiScale, float lineHeightScale = 1)
         {
             // This method is gonna suck due to complexity.
             // Bear with me here.
@@ -112,10 +135,10 @@ namespace Robust.Client.UserInterface
                         continue;
 
                     if (ProcessMetric(ref this, metrics, out breakLine))
-                        return;
+                        return this;
                 }
 
-                if (_tagControls == null || !_tagControls.TryGetValue(nodeIndex, out var control))
+                if (Controls == null || !Controls.TryGetValue(nodeIndex, out var control))
                     continue;
 
                 control.Measure(new Vector2(Width, Height));
@@ -128,12 +151,14 @@ namespace Robust.Client.UserInterface
                     desiredSize.Y);
 
                 if (ProcessMetric(ref this, controlMetrics, out breakLine))
-                    return;
+                    return this;
             }
 
             Width = wordWrap.FinalizeText(out breakLine);
             CheckLineBreak(ref this, breakLine);
 
+            return this;
+
             bool ProcessRune(ref RichTextEntry src, Rune rune, out int? outBreakLine)
             {
                 wordWrap.NextRune(rune, out breakLine, out var breakNewLine, out var skip);
@@ -166,9 +191,10 @@ namespace Robust.Client.UserInterface
 
         internal readonly void HideControls()
         {
-            if (_tagControls == null)
+            if (Controls == null)
                 return;
-            foreach (var control in _tagControls.Values)
+
+            foreach (var control in Controls.Values)
             {
                 control.Visible = false;
             }
@@ -220,7 +246,7 @@ namespace Robust.Client.UserInterface
                     globalBreakCounter += 1;
                 }
 
-                if (_tagControls == null || !_tagControls.TryGetValue(nodeIndex, out var control))
+                if (Controls == null || !Controls.TryGetValue(nodeIndex, out var control))
                     continue;
 
                 // Controls may have been previously hidden via HideControls due to being "out-of frame".
@@ -243,7 +269,7 @@ namespace Robust.Client.UserInterface
                 return node.Value.StringValue ?? "";
 
             //Skip the node if there is no markup tag for it.
-            if (!tagManager.TryGetMarkupTag(node.Name, _tagsAllowed, out var tag))
+            if (!tagManager.TryGetMarkupTagHandler(node.Name, _tagsAllowed, out var tag))
                 return "";
 
             if (!node.Closing)

Robust.Client/Utility/ReloadManager.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
-using System.Linq;
 using System.Threading;
 using Robust.Client.Graphics;
 using Robust.Shared;
@@ -21,12 +20,14 @@ internal sealed class ReloadManager : IReloadManager
     [Dependency] private readonly IConfigurationManager _cfg = default!;
     [Dependency] private readonly ILogManager _logMan = default!;
     [Dependency] private readonly IResourceManager _res = default!;
+#pragma warning disable CS0414
     [Dependency] private readonly ITaskManager _tasks = default!;
+#pragma warning restore CS0414
 
     private readonly TimeSpan _reloadDelay = TimeSpan.FromMilliseconds(10);
     private CancellationTokenSource _reloadToken = new();
     private readonly HashSet<ResPath> _reloadQueue = new();
-    private List<FileSystemWatcher> _watchers = new();
+    private List<FileSystemWatcher> _watchers = new(); // this list is never used but needed to prevent them from being garbage collected
 
     public event Action<ResPath>? OnChanged;
 
@@ -69,6 +70,11 @@ internal sealed class ReloadManager : IReloadManager
         _reloadQueue.Clear();
     }
 
+    public void Register(ResPath directory, string filter)
+    {
+        Register(directory.ToString(), filter);
+    }
+
     public void Register(string directory, string filter)
     {
         if (!_cfg.GetCVar(CVars.ResPrototypeReloadWatch))
@@ -90,7 +96,7 @@ internal sealed class ReloadManager : IReloadManager
                 NotifyFilter = NotifyFilters.LastWrite
             };
 
-            _watchers.Add(watcher);
+            _watchers.Add(watcher); // prevent garbage collection
 
             watcher.Changed += OnWatch;
 
@@ -100,7 +106,7 @@ internal sealed class ReloadManager : IReloadManager
             }
             catch (IOException ex)
             {
-                Logger.Error($"Watching resources in path {path} threw an exception:\n{ex}");
+                _sawmill.Error($"Watching resources in path {path} threw an exception:\n{ex}");
             }
         }
 
@@ -136,6 +142,6 @@ internal sealed class ReloadManager : IReloadManager
                 }
             });
         }
-        #endif
+#endif
     }
 }

Robust.Client/Utility/SpriteSpecifierExt.cs

@@ -17,6 +17,7 @@ namespace Robust.Client.Utility
     /// </summary>
     public static class SpriteSpecifierExt
     {
+        [Obsolete("Use SpriteSystem.GetTexture() instead")]
         public static Texture GetTexture(this SpriteSpecifier.Texture texSpecifier, IResourceCache cache)
         {
             return cache
@@ -24,13 +25,14 @@ namespace Robust.Client.Utility
                 .Texture;
         }
 
-        [Obsolete("Use SpriteSystem")]
+        [Obsolete("Use SpriteSystem.GetState() instead")]
         public static RSI.State GetState(this SpriteSpecifier.Rsi rsiSpecifier, IResourceCache cache)
         {
             if (!cache.TryGetResource<RSIResource>(SpriteSpecifierSerializer.TextureRoot / rsiSpecifier.RsiPath, out var theRsi))
             {
+                var sys = IoCManager.Resolve<IEntitySystemManager>().GetEntitySystem<SpriteSystem>();
                 Logger.Error("SpriteSpecifier failed to load RSI {0}", rsiSpecifier.RsiPath);
-                return SpriteComponent.GetFallbackState(cache);
+                return sys.GetFallbackState();
             }
 
             if (theRsi.RSI.TryGetState(rsiSpecifier.RsiState, out var state))
@@ -39,21 +41,22 @@ namespace Robust.Client.Utility
             }
 
             Logger.Error($"SpriteSpecifier has invalid RSI state '{rsiSpecifier.RsiState}' for RSI: {rsiSpecifier.RsiPath}");
-            return SpriteComponent.GetFallbackState(cache);
+            return IoCManager.Resolve<IEntitySystemManager>().GetEntitySystem<SpriteSystem>().GetFallbackState();
         }
 
-        [Obsolete("Use SpriteSystem")]
+        [Obsolete("Use SpriteSystem.Frame0() instead")]
         public static Texture Frame0(this SpriteSpecifier specifier)
         {
             return specifier.RsiStateLike().Default;
         }
 
+        [Obsolete("Use SpriteSystem.RsiStateLike() instead")]
         public static IDirectionalTextureProvider DirFrame0(this SpriteSpecifier specifier)
         {
             return specifier.RsiStateLike();
         }
 
-        [Obsolete("Use SpriteSystem")]
+        [Obsolete("Use SpriteSystem.RsiStateLike() instead")]
         public static IRsiStateLike RsiStateLike(this SpriteSpecifier specifier)
         {
             var resC = IoCManager.Resolve<IResourceCache>();
@@ -67,10 +70,11 @@ namespace Robust.Client.Utility
 
                 case SpriteSpecifier.EntityPrototype prototypeIcon:
                     var protMgr = IoCManager.Resolve<IPrototypeManager>();
+                    var sys = IoCManager.Resolve<IEntitySystemManager>().GetEntitySystem<SpriteSystem>();
                     if (!protMgr.TryIndex<EntityPrototype>(prototypeIcon.EntityPrototypeId, out var prototype))
                     {
                         Logger.Error("Failed to load PrototypeIcon {0}", prototypeIcon.EntityPrototypeId);
-                        return SpriteComponent.GetFallbackState(resC);
+                        return sys.GetFallbackState();
                     }
 
                     return SpriteComponent.GetPrototypeIcon(prototype, resC);

Robust.Roslyn.Shared/Diagnostics.cs

@@ -39,6 +39,7 @@ public static class Diagnostics
     public const string IdForbidLiteral = "RA0033";
     public const string IdObsoleteInheritance = "RA0034";
     public const string IdObsoleteInheritanceWithMessage = "RA0035";
+    public const string IdDataFieldYamlSerializable = "RA0036";
 
     public static SuppressionDescriptor MeansImplicitAssignment =>
         new SuppressionDescriptor("RADC1000", "CS0649", "Marked as implicitly assigned.");

Robust.Server/BaseServer.cs

@@ -331,6 +331,7 @@ namespace Robust.Server
             // TODO: solve this properly.
             _serializer.Initialize();
 
+            _loc.Initialize();
             _loc.AddLoadedToStringSerializer(_stringSerializer);
 
             //IoCManager.Resolve<IMapLoader>().LoadedMapData +=

Robust.Server/GameObjects/EntitySystems/PointLightSystem.cs

@@ -14,6 +14,19 @@ public sealed class PointLightSystem : SharedPointLightSystem
         base.Initialize();
         SubscribeLocalEvent<PointLightComponent, ComponentGetState>(OnLightGetState);
         SubscribeLocalEvent<PointLightComponent, ComponentStartup>(OnLightStartup);
+        SubscribeLocalEvent<PointLightComponent, ComponentShutdown>(OnLightShutdown);
+        SubscribeLocalEvent<PointLightComponent, MetaFlagRemoveAttemptEvent>(OnFlagRemoveAttempt);
+    }
+
+    private void OnLightShutdown(Entity<PointLightComponent> ent, ref ComponentShutdown args)
+    {
+        UpdatePriority(ent.Owner, ent.Comp, MetaData(ent.Owner));
+    }
+
+    private void OnFlagRemoveAttempt(Entity<PointLightComponent> ent, ref MetaFlagRemoveAttemptEvent args)
+    {
+        if (IsHighPriority(ent.Comp))
+            args.ToRemove &= ~MetaDataFlags.PvsPriority;
     }
 
     private void OnLightStartup(EntityUid uid, PointLightComponent component, ComponentStartup args)
@@ -21,24 +34,14 @@ public sealed class PointLightSystem : SharedPointLightSystem
         UpdatePriority(uid, component, MetaData(uid));
     }
 
-    protected override void UpdatePriority(EntityUid uid, SharedPointLightComponent comp, MetaDataComponent meta)
+    private bool IsHighPriority(SharedPointLightComponent comp)
     {
-        var isHighPriority = comp.Enabled && comp.CastShadows && (comp.Radius > 7);
-        _metadata.SetFlag((uid, meta), MetaDataFlags.PvsPriority, isHighPriority);
+        return comp is {Enabled: true, CastShadows: true, Radius: > 7, LifeStage: <= ComponentLifeStage.Running};
     }
 
-    private void OnLightGetState(EntityUid uid, PointLightComponent component, ref ComponentGetState args)
+    protected override void UpdatePriority(EntityUid uid, SharedPointLightComponent comp, MetaDataComponent meta)
     {
-        args.State = new PointLightComponentState()
-        {
-            Color = component.Color,
-            Enabled = component.Enabled,
-            Energy = component.Energy,
-            Offset = component.Offset,
-            Radius = component.Radius,
-            Softness = component.Softness,
-            CastShadows = component.CastShadows,
-        };
+        _metadata.SetFlag((uid, meta), MetaDataFlags.PvsPriority, IsHighPriority(comp));
     }
 
     public override SharedPointLightComponent EnsureLight(EntityUid uid)

Robust.Server/GameObjects/EntitySystems/ServerOccluderSystem.cs

@@ -9,12 +9,30 @@ public sealed class ServerOccluderSystem : OccluderSystem
 {
     [Dependency] private readonly MetaDataSystem _metadata = default!;
 
+    public override void Initialize()
+    {
+        base.Initialize();
+        SubscribeLocalEvent<OccluderComponent, MetaFlagRemoveAttemptEvent>(OnFlagRemoveAttempt);
+    }
+
+    private void OnFlagRemoveAttempt(Entity<OccluderComponent> ent, ref MetaFlagRemoveAttemptEvent args)
+    {
+        if (ent.Comp is {Enabled: true, LifeStage: <= ComponentLifeStage.Running})
+            args.ToRemove &= ~MetaDataFlags.PvsPriority;
+    }
+
     protected override void OnCompStartup(EntityUid uid, OccluderComponent component, ComponentStartup args)
     {
         base.OnCompStartup(uid, component, args);
         _metadata.SetFlag(uid, MetaDataFlags.PvsPriority, component.Enabled);
     }
 
+    protected override void OnCompRemoved(EntityUid uid, OccluderComponent component, ComponentRemove args)
+    {
+        base.OnCompRemoved(uid, component, args);
+        _metadata.SetFlag(uid, MetaDataFlags.PvsPriority, false);
+    }
+
     public override void SetEnabled(EntityUid uid, bool enabled, OccluderComponent? comp = null, MetaDataComponent? meta = null)
     {
         if (!Resolve(uid, ref comp, false))

Robust.Server/GameStates/PvsSystem.Chunks.cs

@@ -166,11 +166,11 @@ internal sealed partial class PvsSystem
         var session = pvsSession.Session;
         if (session.Status != SessionStatus.InGame)
         {
-            pvsSession.Viewers  = Array.Empty<Entity<TransformComponent, EyeComponent?>>();
+            pvsSession.Viewers = Array.Empty<Entity<TransformComponent, EyeComponent?>>();
             return;
         }
 
-        // Fast path
+        // The majority of players will have no view subscriptions
         if (session.ViewSubscriptions.Count == 0)
         {
             if (session.AttachedEntity is not {} attached)
@@ -184,15 +184,21 @@ internal sealed partial class PvsSystem
             return;
         }
 
+        var count = session.ViewSubscriptions.Count;
         var i = 0;
         if (session.AttachedEntity is { } local)
         {
-            Array.Resize(ref pvsSession.Viewers, session.ViewSubscriptions.Count + 1);
+            if (!session.ViewSubscriptions.Contains(local))
+                count += 1;
+
+            Array.Resize(ref pvsSession.Viewers, count);
+
+            // Attached entity is always the first viewer, to prioritize it and help reduce pop-in for the "main" eye.
             pvsSession.Viewers[i++] = (local, Transform(local), _eyeQuery.CompOrNull(local));
         }
         else
         {
-            Array.Resize(ref pvsSession.Viewers, session.ViewSubscriptions.Count);
+            Array.Resize(ref pvsSession.Viewers, count);
         }
 
         foreach (var ent in session.ViewSubscriptions)
@@ -200,6 +206,8 @@ internal sealed partial class PvsSystem
             if (ent != session.AttachedEntity)
                 pvsSession.Viewers[i++] =  (ent, Transform(ent), _eyeQuery.CompOrNull(ent));
         }
+
+        DebugTools.AssertEqual(i, pvsSession.Viewers.Length);
     }
 
     private void ProcessVisibleChunks()

Robust.Server/Localization/ServerLocalizationManager.cs

@@ -0,0 +1,8 @@
+using Robust.Shared.Localization;
+
+namespace Robust.Server.Localization;
+
+internal sealed class ServerLocalizationManager : LocalizationManager, ILocalizationManager
+{
+    void ILocalizationManager.Initialize() => Initialize();
+}

Robust.Server/Physics/Commands/BoxStackCommand.cs

@@ -0,0 +1,82 @@
+using System.Collections.Generic;
+using System.Numerics;
+using Robust.Shared.Console;
+using Robust.Shared.GameObjects;
+using Robust.Shared.IoC;
+using Robust.Shared.Map;
+using Robust.Shared.Physics;
+using Robust.Shared.Physics.Collision.Shapes;
+using Robust.Shared.Physics.Components;
+using Robust.Shared.Physics.Controllers;
+using Robust.Shared.Physics.Dynamics;
+using Robust.Shared.Physics.Systems;
+
+namespace Robust.Server.Physics.Commands;
+
+public sealed class BoxStackCommand : IConsoleCommand
+{
+    [Dependency] private readonly IEntityManager _entManager = default!;
+
+    public string Command => "boxstack";
+    public string Description => string.Empty;
+    public string Help => "boxstack [mapid] [columns] [rows]";
+    public void Execute(IConsoleShell shell, string argStr, string[] args)
+    {
+        if (args.Length != 3 ||
+            !int.TryParse(args[0], out var mapInt) ||
+            !int.TryParse(args[1], out var columns) ||
+            !int.TryParse(args[2], out var rows))
+        {
+            return;
+        }
+
+        var mapId = new MapId(mapInt);
+
+        var fixtureSystem = _entManager.System<FixtureSystem>();
+        var physSystem = _entManager.System<SharedPhysicsSystem>();
+        physSystem.SetGravity(new Vector2(0f, -9.8f));
+
+        var groundUid = _entManager.SpawnEntity(null, new MapCoordinates(0, 0, mapId));
+        var ground = _entManager.AddComponent<PhysicsComponent>(groundUid);
+        var groundManager = _entManager.EnsureComponent<FixturesComponent>(groundUid);
+
+        var horizontal = new EdgeShape(new Vector2(-40, 0), new Vector2(40, 0));
+        fixtureSystem.CreateFixture(groundUid, "fix1", new Fixture(horizontal, 1, 1, true), manager: groundManager, body: ground);
+
+        var vertical = new EdgeShape(new Vector2(10, 0), new Vector2(10, 10));
+        fixtureSystem.CreateFixture(groundUid, "fix2", new Fixture(vertical, 1, 1, true), manager: groundManager, body: ground);
+
+        physSystem.WakeBody(groundUid, manager: groundManager, body: ground);
+
+        var xs = new[]
+        {
+            0.0f, -10.0f, -5.0f, 5.0f, 10.0f
+        };
+
+        for (var j = 0; j < columns; j++)
+        {
+            for (var i = 0; i < rows; i++)
+            {
+                var x = 0.0f;
+
+                var boxUid = _entManager.SpawnEntity(null,
+                    new MapCoordinates(new Vector2(xs[j] + x, 0.55f + 2.1f * i), mapId));
+                var box = _entManager.AddComponent<PhysicsComponent>(boxUid);
+                var manager = _entManager.EnsureComponent<FixturesComponent>(boxUid);
+
+                physSystem.SetBodyType(boxUid, BodyType.Dynamic, manager: manager, body: box);
+                var poly = new PolygonShape(0.001f);
+                poly.Set(new List<Vector2>()
+                {
+                    new(0.5f, -0.5f),
+                    new(0.5f, 0.5f),
+                    new(-0.5f, 0.5f),
+                    new(-0.5f, -0.5f),
+                });
+
+                fixtureSystem.CreateFixture(boxUid, "fix1", new Fixture(poly, 1, 1, true), manager: manager, body: box);
+                physSystem.WakeBody(boxUid, manager: manager, body: box);
+            }
+        }
+    }
+}

Robust.Server/Placement/PlacementManager.cs

@@ -140,7 +140,7 @@ namespace Robust.Server.Placement
             {
                 // Replace existing entities if relevant.
                 if (msg.Replacement && _prototype.Index<EntityPrototype>(entityTemplateName).Components.TryGetValue(
-                        _factory.GetComponentName(typeof(PlacementReplacementComponent)), out var compRegistry))
+                        _factory.GetComponentName<PlacementReplacementComponent>(), out var compRegistry))
                 {
                     var key = ((PlacementReplacementComponent)compRegistry.Component).Key;
                     var gridUid = _xformSystem.GetGrid(coordinates);
@@ -179,11 +179,14 @@ namespace Robust.Server.Placement
             }
             else
             {
-                PlaceNewTile(tileType, coordinates, msg.MsgChannel.UserId);
+                if (_tileDefinitionManager[tileType].AllowRotationMirror)
+                    PlaceNewTile(tileType, coordinates, msg.MsgChannel.UserId, Tile.DirectionToByte(dirRcv), msg.Mirrored);
+                else
+                    PlaceNewTile(tileType, coordinates, msg.MsgChannel.UserId, Tile.DirectionToByte(Direction.South), false);
             }
         }
 
-        private void PlaceNewTile(int tileType, EntityCoordinates coordinates, NetUserId placingUserId)
+        private void PlaceNewTile(int tileType, EntityCoordinates coordinates, NetUserId placingUserId, byte direction, bool mirrored)
         {
             if (!coordinates.IsValid(_entityManager)) return;
 
@@ -193,7 +196,7 @@ namespace Robust.Server.Placement
             if (_entityManager.TryGetComponent(coordinates.EntityId, out grid)
                 || _mapManager.TryFindGridAt(_xformSystem.ToMapCoordinates(coordinates), out gridId, out grid))
             {
-                _maps.SetTile(gridId, grid, coordinates, new Tile(tileType));
+                _maps.SetTile(gridId, grid, coordinates, new Tile(tileType, rotationMirroring: (byte)(direction + (mirrored ? 4 : 0))));
 
                 var placementEraseEvent = new PlacementTileEvent(tileType, coordinates, placingUserId);
                 _entityManager.EventBus.RaiseEvent(EventSource.Local, placementEraseEvent);
@@ -207,7 +210,7 @@ namespace Robust.Server.Placement
 
                 _xformSystem.SetWorldPosition(newGridXform, coordinates.Position - newGrid.Comp.TileSizeHalfVector); // assume bottom left tile origin
                 var tilePos = _maps.WorldToTile(newGrid.Owner, newGrid.Comp, coordinates.Position);
-                _maps.SetTile(newGrid.Owner, newGrid.Comp, tilePos, new Tile(tileType));
+                _maps.SetTile(newGrid.Owner, newGrid.Comp, tilePos, new Tile(tileType, rotationMirroring: (byte)(direction + (mirrored ? 4 : 0))));
 
                 var placementEraseEvent = new PlacementTileEvent(tileType, coordinates, placingUserId);
                 _entityManager.EventBus.RaiseEvent(EventSource.Local, placementEraseEvent);

Robust.Server/Prototypes/ServerPrototypeManager.cs

@@ -13,8 +13,10 @@ namespace Robust.Server.Prototypes
 {
     public sealed class ServerPrototypeManager : PrototypeManager
     {
+#pragma warning disable CS0414
         [Dependency] private readonly IPlayerManager _playerManager = default!;
         [Dependency] private readonly IConGroupController _conGroups = default!;
+#pragma warning restore CS0414
         [Dependency] private readonly INetManager _netManager = default!;
         [Dependency] private readonly IBaseServerInternal _server = default!;
 

Robust.Server/ServerIoC.cs

@@ -4,6 +4,7 @@ using Robust.Server.Console;
 using Robust.Server.DataMetrics;
 using Robust.Server.GameObjects;
 using Robust.Server.GameStates;
+using Robust.Server.Localization;
 using Robust.Server.Placement;
 using Robust.Server.Player;
 using Robust.Server.Prototypes;
@@ -21,6 +22,7 @@ using Robust.Shared.Console;
 using Robust.Shared.ContentPack;
 using Robust.Shared.GameObjects;
 using Robust.Shared.IoC;
+using Robust.Shared.Localization;
 using Robust.Shared.Map;
 using Robust.Shared.Network;
 using Robust.Shared.Player;
@@ -97,7 +99,9 @@ namespace Robust.Server
             deps.Register<NetworkResourceManager>();
             deps.Register<IHttpClientHolder, HttpClientHolder>();
             deps.Register<UploadedContentManager>();
-             deps.Register<IHWId, DummyHWId>();
+            deps.Register<IHWId, DummyHWId>();
+            deps.Register<ILocalizationManager, ServerLocalizationManager>();
+            deps.Register<ILocalizationManagerInternal, ServerLocalizationManager>();
         }
     }
 }

Robust.Shared.Maths/Angle.cs

@@ -104,6 +104,16 @@ namespace Robust.Shared.Maths
             return (Direction) (Math.Floor((ang + CardinalOffset) / CardinalSegment) * 2 % 8);
         }
 
+        /// <summary>
+        /// Rounds the angle to the nearest cardinal direction. This behaves similarly to a combination of
+        /// <see cref="GetCardinalDir"/> and Direction.ToAngle(), however this may return an angle outside of the range
+        /// returned by those methods (-pi to pi).
+        /// </summary>
+        public Angle RoundToCardinalAngle()
+        {
+            return new Angle(CardinalSegment * Math.Floor((Theta + CardinalOffset) / CardinalSegment));
+        }
+
         /// <summary>
         ///     Rotates the vector counter-clockwise around its origin by the value of Theta.
         /// </summary>

Robust.Shared.Maths/Box2i.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics.Contracts;
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
@@ -101,6 +102,7 @@ namespace Robust.Shared.Maths
         /// <summary>
         ///     Returns the smallest rectangle that contains both of the rectangles.
         /// </summary>
+        [Pure]
         public readonly Box2i Union(in Box2i other)
         {
             var botLeft = Vector2i.ComponentMin(BottomLeft, other.BottomLeft);
@@ -207,6 +209,7 @@ namespace Robust.Shared.Maths
         /// <summary>
         /// Multiplies each side of the box by the scalar.
         /// </summary>
+        [Pure]
         public Box2i Scale(int scalar)
         {
             return new Box2i(
@@ -215,6 +218,21 @@ namespace Robust.Shared.Maths
                 Right * scalar,
                 Top * scalar);
         }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [Pure]
+        public bool Intersects(in Box2i other)
+        {
+            return other.Bottom <= this.Top && other.Top >= this.Bottom && other.Right >= this.Left &&
+                   other.Left <= this.Right;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [Pure]
+        public readonly Box2i Enlarged(int size)
+        {
+            return new(Left - size, Bottom - size, Right + size, Top + size);
+        }
     }
 
     /// <summary>

Robust.Shared/Audio/ResolvedSoundSpecifier.cs

@@ -13,7 +13,8 @@ namespace Robust.Shared.Audio;
 /// <seealso cref="ResolvedPathSpecifier"/>
 /// <seealso cref="ResolvedCollectionSpecifier"/>
 [Serializable, NetSerializable]
-public abstract partial class ResolvedSoundSpecifier {
+public abstract partial class ResolvedSoundSpecifier
+{
     [Obsolete("String literals for sounds are deprecated, use a SoundSpecifier or ResolvedSoundSpecifier as appropriate instead")]
     public static implicit operator ResolvedSoundSpecifier(string s) => new ResolvedPathSpecifier(s);
     [Obsolete("String literals for sounds are deprecated, use a SoundSpecifier or ResolvedSoundSpecifier as appropriate instead")]
@@ -22,8 +23,10 @@ public abstract partial class ResolvedSoundSpecifier {
     /// <summary>
     /// Returns whether <c>s</c> is null, or if it contains an empty path/collection ID.
     /// </summary>
-    public static bool IsNullOrEmpty(ResolvedSoundSpecifier? s) {
-        return s switch {
+    public static bool IsNullOrEmpty(ResolvedSoundSpecifier? s)
+    {
+        return s switch
+        {
             null => true,
             ResolvedPathSpecifier path => path.Path.ToString() == "",
             ResolvedCollectionSpecifier collection => string.IsNullOrEmpty(collection.Collection),
@@ -37,7 +40,8 @@ public abstract partial class ResolvedSoundSpecifier {
 /// </summary>
 /// <seealso cref="ResolvedCollectionSpecifier"/>
 [Serializable, NetSerializable]
-public sealed partial class ResolvedPathSpecifier : ResolvedSoundSpecifier {
+public sealed partial class ResolvedPathSpecifier : ResolvedSoundSpecifier, IEquatable<ResolvedPathSpecifier>
+{
     /// <summary>
     /// The resource path of the sound.
     /// </summary>
@@ -57,6 +61,21 @@ public sealed partial class ResolvedPathSpecifier : ResolvedSoundSpecifier {
     public ResolvedPathSpecifier(string path) : this(new ResPath(path))
     {
     }
+
+    public bool Equals(ResolvedPathSpecifier? other)
+    {
+        return Path.Equals(other?.Path);
+    }
+
+    public override bool Equals(object? obj)
+    {
+        return Equals(obj as ResolvedPathSpecifier);
+    }
+
+    public override int GetHashCode()
+    {
+        return Path.GetHashCode();
+    }
 }
 
 /// <summary>
@@ -64,7 +83,9 @@ public sealed partial class ResolvedPathSpecifier : ResolvedSoundSpecifier {
 /// </summary>
 /// <seealso cref="ResolvedPathSpecifier"/>
 [Serializable, NetSerializable]
-public sealed partial class ResolvedCollectionSpecifier : ResolvedSoundSpecifier {
+public sealed partial class ResolvedCollectionSpecifier : ResolvedSoundSpecifier, IEquatable<ResolvedCollectionSpecifier>
+{
+
     /// <summary>
     /// The ID of the <see cref="SoundCollectionPrototype">sound collection</see> to look up.
     /// </summary>
@@ -87,4 +108,19 @@ public sealed partial class ResolvedCollectionSpecifier : ResolvedSoundSpecifier
         Collection = collection;
         Index = index;
     }
+
+    public bool Equals(ResolvedCollectionSpecifier? other)
+    {
+        return Collection.Equals(other?.Collection) && Index.Equals(other?.Index);
+    }
+
+    public override bool Equals(object? obj)
+    {
+        return Equals(obj as ResolvedCollectionSpecifier);
+    }
+
+    public override int GetHashCode()
+    {
+        return HashCode.Combine(Collection, Index);
+    }
 }