Harder DynamicTree against NaN.

B2DynamicTree<T> has asserts, DynamicTree<T> handles them gracefully.

NaNs in DynamicTree were causing the internal state to corrupt resulting in the sprite flickering issues.

Fixes https://github.com/space-wizards/space-station-14/issues/2896

Robust.Shared/Physics/B2DynamicTree.cs

@@ -18,6 +18,8 @@
  * 3. This notice may not be removed or altered from any source distribution.
  */
 
+// #define DEBUG_DYNAMIC_TREE
+
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -268,6 +270,9 @@ namespace Robust.Shared.Physics
         /// </summary>
         public Proxy CreateProxy(in Box2 aabb, T userData)
         {
+            // Also catches NaN fuckery.
+            Assert(aabb.Right >= aabb.Left && aabb.Top >= aabb.Bottom);
+
             ref var proxy = ref AllocateNode(out var proxyId);
 
             // Fatten the aabb.
@@ -292,6 +297,8 @@ namespace Robust.Shared.Physics
         public bool MoveProxy(Proxy proxy, in Box2 aabb, Vector2 displacement)
         {
             Assert(0 <= proxy && proxy < Capacity);
+            // Also catches NaN fuckery.
+            Assert(aabb.Right >= aabb.Left && aabb.Top >= aabb.Bottom);
 
             ref var leafNode = ref _nodes[proxy];
 

Robust.Shared/Physics/DynamicTree.cs

@@ -71,7 +71,7 @@ namespace Robust.Shared.Physics
         private readonly ExtractAabbDelegate _extractAabb;
 
         // avoids "Collection was modified; enumeration operation may not execute."
-        private IDictionary<T, Proxy> _nodeLookup;
+        private Dictionary<T, Proxy> _nodeLookup;
         private readonly B2DynamicTree<T> _b2Tree;
 
         public DynamicTree(ExtractAabbDelegate extractAabbFunc, IEqualityComparer<T>? comparer = null, float aabbExtendSize = 1f / 32, int capacity = 256, Func<int, int>? growthFunc = null)
@@ -134,6 +134,12 @@ namespace Robust.Shared.Physics
 
             var box = _extractAabb(item);
 
+            if (CheckNaNs(box))
+            {
+                _nodeLookup[item] = Proxy.Free;
+                return true;
+            }
+
             proxy = _b2Tree.CreateProxy(box, item);
             _nodeLookup[item] = proxy;
 
@@ -162,7 +168,11 @@ namespace Robust.Shared.Physics
                 return false;
             }
 
-            _b2Tree.DestroyProxy(proxy);
+            if (proxy != Proxy.Free)
+            {
+                _b2Tree.DestroyProxy(proxy);
+            }
+
             return true;
         }
 
@@ -178,6 +188,25 @@ namespace Robust.Shared.Physics
             }
 
             var newBox = _extractAabb(item);
+
+            if (CheckNaNs(newBox))
+            {
+                if (proxy == Proxy.Free)
+                {
+                    return false;
+                }
+
+                _b2Tree.DestroyProxy(proxy);
+                _nodeLookup[item] = Proxy.Free;
+                return true;
+            }
+
+            if (proxy == Proxy.Free)
+            {
+                _nodeLookup[item] = _b2Tree.CreateProxy(newBox, item);
+                return true;
+            }
+
             return _b2Tree.MoveProxy(proxy, newBox, Vector2.Zero);
         }
 
@@ -304,6 +333,14 @@ namespace Robust.Shared.Physics
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public bool AddOrUpdate(T item) => Update(item) || Add(item);
 
+        private static bool CheckNaNs(in Box2 box)
+        {
+            return float.IsNaN(box.Left)
+                   || float.IsNaN(box.Top)
+                   || float.IsNaN(box.Bottom)
+                   || float.IsNaN(box.Right);
+        }
+
         [Conditional("DEBUG_DYNAMIC_TREE")]
         [Conditional("DEBUG_DYNAMIC_TREE_ASSERTS")]
         [DebuggerNonUserCode]