Re-implement block hit decals

- Implement BlockEntity more
- Add INotifyChildRemoved which
  works with RemoveFromParent
- IChunkLayer.Changed now reports BlockPos

src/Objects/Bullet.cs

@@ -34,18 +34,24 @@ public class Bullet : Node2D
     {
         // TODO: Add a global game setting to specify whether shooter or server announces successful hit.
         //       For now, server is the most straight-forward. Eventually, support client predictive movement?
-        if (!(this.GetGame() is Server) || !(obj.GetNodeOrNull("Sprite") is Sprite sprite)) return;
+        if (!(this.GetGame() is Server)) return;
         var world = this.GetWorld();
-        var path  = world.GetPathTo(sprite);
         var color = new Color(Color, (1 + Color.a) / 2);
-        RPC.Reliable(world.GetPlayersTracking(BlockPos.FromVector(obj.GlobalPosition).ToChunkPos()),
+        if (obj.GetParent() is Chunk chunk) {
-            world.SpawnHit, path, hitPosition, color);
+            var path = world.GetPathTo(chunk);
+            var to   = world.GetPlayersTracking(chunk.ChunkPos);
+            RPC.Reliable(to, world.SpawnHit, path, hitPosition, color);
+        } else if (obj.GetNodeOrNull("Sprite") is Sprite sprite) {
+            var path = world.GetPathTo(sprite);
+            var to   = world.GetPlayersTracking(BlockPos.FromVector(obj.GlobalPosition).ToChunkPos());
+            RPC.Reliable(to, world.SpawnHit, path, hitPosition, color);
             if (obj is Player player) {
                 var rangeFactor = Math.Min(1.0F, (MaximumRange - _distance) / (MaximumRange - EffectiveRange));
                 player.Health -= Damage * rangeFactor;
             }
             // TODO: Also spawn a ghost of the player who was hit so they can see where they got shot?
         }
+    }
 
     public override void _Ready()
         { if (this.GetGame() is Server) Visible = false; }

src/Objects/HitDecal.cs

@@ -34,4 +34,37 @@ public class HitDecal : Sprite
             if (Modulate.a <= 0) this.RemoveFromParent();
         }
     }
+
+    public static void Spawn(World world, NodePath path, Vector2 hitPosition, Color color)
+    {
+        var decal = GD.Load<Texture>("res://gfx/hit_decal.png");
+        var node  = world.GetNode(path);
+        switch (node) {
+            case Sprite sprite:
+                node.AddChild(new HitDecal(decal, sprite.Texture, hitPosition, color));
+                break;
+            case Chunk chunk:
+                hitPosition += chunk.Position;
+                var start = BlockPos.FromVector((hitPosition - decal.GetSize() / 2).Floor());
+                var end   = BlockPos.FromVector((hitPosition + decal.GetSize() / 2).Ceil());
+                for (var x = start.X; x <= end.X; x++)
+                for (var y = start.Y; y <= end.Y; y++) {
+                    var blockPos = new BlockPos(x, y);
+                    var texture  = world[blockPos].Get<Block>().Texture;
+                    if (texture == null) continue;
+                    world[blockPos].GetOrCreate<HitDecals>().AddChild(new HitDecal(
+                        decal, texture, hitPosition - blockPos.ToVector(), color));
+                }
+                break;
+        }
+    }
+}
+
+public class HitDecals : Node2D, INotifyChildRemoved
+{
+    public void OnChildRemoved(Node child)
+    {
+        if (GetChildCount() == 0)
+            this.RemoveFromParent();
+    }
 }

src/Utility/Extensions.cs

@@ -16,6 +16,10 @@ public static class Extensions
 
     public static IEnumerable<T> GetChildren<T>(this Node node)
         => node.GetChildren().Cast<T>();
+    public static T GetOrCreateChild<T>(this Node node)
+        where T : Node, new() => node.GetOrCreateChild<T>(typeof(T).Name, () => new T());
+    public static T GetOrCreateChild<T>(this Node node, string name)
+        where T : Node, new() => node.GetOrCreateChild<T>(name, () => new T());
     public static T GetOrCreateChild<T>(this Node node, string name, Func<T> createFunc)
         where T : Node
     {
@@ -39,8 +43,10 @@ public static class Extensions
     }
     public static void RemoveFromParent(this Node node)
     {
+        var notifyParent = node.GetParent() as INotifyChildRemoved;
         node.GetParent().RemoveChild(node);
         node.QueueFree();
+        notifyParent?.OnChildRemoved(node);
     }
 
     public static float NextFloat(this Random random)
@@ -59,3 +65,11 @@ public static class Extensions
     public static void Deconstruct<TKey, TValue>(this KeyValuePair<TKey, TValue> kvp, out TKey key, out TValue value)
         { key = kvp.Key; value = kvp.Value; }
 }
+
+/// <summary> When a child is removed from this Node using
+///           <see cref="Extensions.RemoveFromParent"/>,
+///           the OnChildRemoved method is called. </summary>
+public interface INotifyChildRemoved
+{
+    void OnChildRemoved(Node child);
+}

src/World/Block/BlockEntity.cs

@@ -1,6 +1,19 @@
 using Godot;
 
-public class BlockEntity : Node2D
+// TODO: Add saving of block entities.
+public class BlockEntity : Node2D, INotifyChildRemoved
 {
+    public BlockRef Block { get; }
 
+    public BlockEntity(BlockRef block)
+    {
+        Block    = block;
+        Position = block.Position.GlobalToChunkRel().ToVector();
+    }
+
+    public void OnChildRemoved(Node child)
+    {
+        if (GetChildCount() == 0)
+            this.RemoveFromParent();
+    }
 }

src/World/Block/BlockRef.cs

@@ -21,6 +21,8 @@ public class BlockRef
 
     public BlockEntity GetEntity(bool create)
         => GetChunk(create)?.GetBlockEntity(Position.GlobalToChunkRel(), create);
+    public void RemoveEntity()
+        => GetChunk(false)?.RemoveBlockEntity(Position.GlobalToChunkRel());
 
 
     public T Get<T>()
@@ -47,4 +49,8 @@ public class BlockRef
             entity.AddChild((Node)(object)value);
         } else throw new ArgumentException($"Unable to access {typeof(T).Name} on a Block", nameof(T));
     }
+
+    // TODO: Clear block entity when last child is removed?
+    public void Remove<T>() where T : Node
+        => GetEntity(false)?.GetNode(typeof(T).Name)?.RemoveFromParent();
 }

src/World/Chunk/Chunk.cs

@@ -49,17 +49,30 @@ public partial class Chunk : Node2D
         }
         return layer;
     }
-    public void OnLayerChanged(IChunkLayer layer)
+
-        => _dirty = true;
+    public void OnLayerChanged(IChunkLayer layer, BlockPos pos)
+    {
+        _dirty = true;
+        // Clear block entity if block is changed.
+        if (layer is BlockLayer) RemoveBlockEntity(pos);
+    }
 
 
     public BlockEntity GetBlockEntity(BlockPos pos, bool create)
     {
         EnsureWithinBounds(pos);
-        return create ? this.GetOrCreateChild(pos.ToString(), () => new BlockEntity())
+        return create ? this.GetOrCreateChild(pos.ToString(), () =>
+                          new BlockEntity(new BlockRef(this.GetWorld(),
+                              pos.ChunkRelToGlobal(ChunkPos))))
                       : GetNode<BlockEntity>(pos.ToString());
     }
 
+    public void RemoveBlockEntity(BlockPos pos)
+    {
+        EnsureWithinBounds(pos);
+        GetNode(pos.ToString())?.RemoveFromParent();
+    }
+
 
     public static void EnsureWithinBounds(BlockPos pos)
     {

src/World/Chunk/ChunkLayer.cs

@@ -12,14 +12,14 @@ public interface IChunkLayer : IDeSerializable
 {
     Type AccessType { get; }
     bool IsDefault { get; }
-    event Action<IChunkLayer> Changed;
+    event Action<IChunkLayer, BlockPos> Changed;
 }
 
 public interface IChunkLayer<T> : IChunkLayer
 {
     T this[BlockPos pos] { get; set; }
     T this[int x, int y] { get; set; }
-    T this[int index] { get; set; }
+    T this[int index] { get; }
 }
 
 public class ArrayChunkLayer<T> : IChunkLayer<T>
@@ -32,26 +32,24 @@ public class ArrayChunkLayer<T> : IChunkLayer<T>
     public Type AccessType => typeof(T);
     public bool IsDefault  => NonDefaultCount == 0;
 
-    public event Action<IChunkLayer> Changed;
+    public event Action<IChunkLayer, BlockPos> Changed;
 
-    public T this[BlockPos pos] {
+    public T this[int index] => _data[index];
-        get => this[Chunk.GetIndex(pos)];
-        set => this[Chunk.GetIndex(pos)] = value;
-    }
     public T this[int x, int y] {
         get => this[Chunk.GetIndex(x, y)];
-        set => this[Chunk.GetIndex(x, y)] = value;
+        set => this[new BlockPos(x, y)] = value;
     }
-    public T this[int index] {
+    public T this[BlockPos pos] {
-        get => _data[index];
+        get => this[Chunk.GetIndex(pos.X, pos.Y)];
         set {
+            var index = Chunk.GetIndex(pos.X, pos.Y);
             var previous = _data[index];
             if (COMPARER.Equals(value, previous)) return;
             _data[index] = value;
 
             if (!COMPARER.Equals(previous, default)) NonDefaultCount--;
             if (!COMPARER.Equals(value, default)) NonDefaultCount++;
-            Changed?.Invoke(this);
+            Changed?.Invoke(this, pos);
         }
     }
 
@@ -78,10 +76,10 @@ public class TranslationLayer<TData, TAccess> : IChunkLayer<TAccess>
 
     public Type AccessType => typeof(TAccess);
     public bool IsDefault  => _data.IsDefault;
-    public event Action<IChunkLayer> Changed { add => _data.Changed += value; remove => _data.Changed -= value; }
+    public event Action<IChunkLayer, BlockPos> Changed { add => _data.Changed += value; remove => _data.Changed -= value; }
     public TAccess this[BlockPos pos] { get => _from(_data[pos]); set => _data[pos] = _to(value); }
     public TAccess this[int x, int y] { get => _from(_data[x, y]); set => _data[x, y] = _to(value); }
-    public TAccess this[int index] { get => _from(_data[index]); set => _data[index] = _to(value); }
+    public TAccess this[int index] => _from(_data[index]);
 
     public void Serialize(ref MessagePackWriter writer, MessagePackSerializerOptions options)
         => _data.Serialize(ref writer, options);

src/World/World.cs

@@ -97,13 +97,8 @@ public partial class World : Node
     }
 
     [Puppet]
-    public void SpawnHit(NodePath spritePath, Vector2 hitPosition, Color color)
+    public void SpawnHit(NodePath path, Vector2 hitPosition, Color color)
-    {
+        => HitDecal.Spawn(this.GetWorld(), path, hitPosition, color);
-        var texture = GD.Load<Texture>("res://gfx/hit_decal.png");
-        var sprite  = this.GetWorld().GetNode<Sprite>(spritePath);
-        var hit     = new HitDecal(texture, sprite.Texture, hitPosition, color);
-        sprite.AddChild(hit);
-    }
 
     [PuppetSync]
     public void Despawn(NodePath path, bool errorIfMissing)