RobustToolbox/Robust.Shared/ComponentTrees/RecursiveMoveSystem.cs

using Robust.Shared.GameObjects;
using Robust.Shared.IoC;
using Robust.Shared.Map;
using Robust.Shared.Utility;

namespace Robust.Shared.ComponentTrees;

/// <summary>
///     This system will recursively raise events to update component tree positions any time any entity moves.
/// </summary>
/// <remarks>
///     This is used by some client-side systems (e.g., sprites, lights, etc). However this can be quite expensive and if possible should not be used by the server.
/// </remarks>
internal sealed class RecursiveMoveSystem : EntitySystem
{
    [Dependency] private readonly IMapManager _mapManager = default!;
    [Dependency] private readonly SharedTransformSystem _transform = default!;

    public delegate void TreeRecursiveMoveEventHandler(EntityUid uid, TransformComponent xform);

    public event TreeRecursiveMoveEventHandler? OnTreeRecursiveMove;

    private EntityQuery<TransformComponent> _xformQuery;

    bool _subscribed = false;

    public override void Initialize()
    {
        base.Initialize();
        _xformQuery = GetEntityQuery<TransformComponent>();
    }

    public override void Shutdown()
    {
        if (_subscribed)
            _transform.OnGlobalMoveEvent -= AnythingMoved;

        _subscribed = false;
    }

    internal void AddSubscription()
    {
        if (_subscribed)
            return;

        _subscribed = true;
        _transform.OnGlobalMoveEvent += AnythingMoved;
    }

    private void AnythingMoved(ref MoveEvent args)
    {
        if (args.Component.MapUid == args.Sender || args.Component.GridUid == args.Sender)
            return;

        DebugTools.Assert(!_mapManager.IsMap(args.Sender));
        DebugTools.Assert(!_mapManager.IsGrid(args.Sender));

        AnythingMovedSubHandler(args.Sender, args.Component);
    }

    private void AnythingMovedSubHandler(
        EntityUid uid,
        TransformComponent xform)
    {
        OnTreeRecursiveMove?.Invoke(uid, xform);

        // TODO only enumerate over entities in containers if necessary?
        // annoyingly, containers aren't guaranteed to occlude sprites & lights
        // but AFAIK thats currently unused???

        foreach (var child in xform._children)
        {
            if (_xformQuery.TryGetComponent(child, out var childXform))
                AnythingMovedSubHandler(child, childXform);
        }
    }
}