Don't allocate a draw list if visual doesn't render anything

src/Avalonia.Base/Rendering/Composition/CompositingRenderer.cs

@@ -223,7 +223,7 @@ public class CompositingRenderer : IRendererWithCompositor
 
             comp.TransformMatrix = MatrixUtils.ToMatrix4x4(renderTransform);
 
-            _recorder.BeginUpdate(comp.DrawList ?? new CompositionDrawList());
+            _recorder.BeginUpdate(comp.DrawList);
             visual.Render(_recordingContext);
             comp.DrawList = _recorder.EndUpdate();
 

src/Avalonia.Base/Rendering/Composition/Drawing/CompositionDrawList.cs

@@ -64,7 +64,8 @@ internal class CompositionDrawListBuilder
         _owns = false;
     }
 
-    public CompositionDrawList DrawOperations => _operations ?? new CompositionDrawList();
+    public int Count => _operations?.Count ?? 0;
+    public CompositionDrawList? DrawOperations => _operations;
 
     void MakeWritable(int atIndex)
     {
@@ -84,18 +85,18 @@ internal class CompositionDrawListBuilder
     public void ReplaceDrawOperation(int index, IDrawOperation node)
     {
         MakeWritable(index);
-        DrawOperations.Add(RefCountable.Create(node));
+        DrawOperations!.Add(RefCountable.Create(node));
     }
 
     public void AddDrawOperation(IDrawOperation node)
     {
-        MakeWritable(DrawOperations.Count);
-        DrawOperations.Add(RefCountable.Create(node));
+        MakeWritable(Count);
+        DrawOperations!.Add(RefCountable.Create(node));
     }
 
     public void TrimTo(int count)
     {
-        if (count < DrawOperations.Count)
-            DrawOperations.RemoveRange(count, DrawOperations.Count - count);
+        if (count < Count)
+            _operations!.RemoveRange(count, _operations.Count - count);
     }
 }

src/Avalonia.Base/Rendering/Composition/Drawing/CompositionDrawingContext.cs

@@ -344,7 +344,7 @@ internal class CompositionDrawingContext : IDrawingContextImpl, IDrawingContextW
 
     private void Add<T>(T node) where T : class, IDrawOperation
     {
-        if (_drawOperationIndex < _builder!.DrawOperations.Count)
+        if (_drawOperationIndex < _builder.Count)
         {
             _builder.ReplaceDrawOperation(_drawOperationIndex, node);
         }
@@ -358,8 +358,8 @@ internal class CompositionDrawingContext : IDrawingContextImpl, IDrawingContextW
 
     private IRef<T>? NextDrawAs<T>() where T : class, IDrawOperation
     {
-        return _drawOperationIndex < _builder!.DrawOperations.Count
-            ? _builder.DrawOperations[_drawOperationIndex] as IRef<T>
+        return _drawOperationIndex < _builder.Count
+            ? _builder.DrawOperations![_drawOperationIndex] as IRef<T>
             : null;
     }