More work on deferred renderer.

Getting opacity layers working.

src/Avalonia.Visuals/Rendering/DisplayDirtyRect.cs

@@ -4,7 +4,7 @@ namespace Avalonia.Rendering
 {
     public class DisplayDirtyRect
     {
-        public static readonly TimeSpan TimeToLive = TimeSpan.FromMilliseconds(500);
+        public static readonly TimeSpan TimeToLive = TimeSpan.FromMilliseconds(250);
 
         public DisplayDirtyRect(Rect rect)
         {

src/Avalonia.Visuals/Rendering/RenderLayers.cs

@@ -47,7 +47,7 @@ namespace Avalonia.Rendering
                 var layer = _inner[i];
                 var node = (VisualNode)scene.FindNode(layer.LayerRoot);
 
-                if (node == null || node.LayerRoot != layer.LayerRoot)
+                if (node == null || node.LayerRoot.VisualRoot == null || node.LayerRoot != layer.LayerRoot)
                 {
                     layer.Bitmap.Dispose();
                     _inner.RemoveAt(i);

src/Avalonia.Visuals/Rendering/SceneGraph/SceneBuilder.cs

@@ -154,11 +154,11 @@ namespace Avalonia.Rendering.SceneGraph
                     node.Opacity = opacity;
                     node.OpacityMask = visual.OpacityMask;
 
-                    if (opacity < 1)
+                    if (opacity < 1 && node.LayerRoot != visual)
                     {
-                        SetLayer(node, node.Visual);
+                        SetLayer(node, node.Visual, contextImpl.Dirty);
                     }
-                    else if (node.LayerRoot == node.Visual && node.Parent != null)
+                    else if (opacity >= 1 && node.LayerRoot == node.Visual && node.Parent != null)
                     {
                         ClearLayer(node, contextImpl.Dirty);
                     }
@@ -185,10 +185,6 @@ namespace Avalonia.Rendering.SceneGraph
                         node.SubTreeUpdated = true;
                         contextImpl.TrimChildren();
                     }
-                    else if (node.OpacityChanged)
-                    {
-                        AddSubtreeBounds(node, contextImpl.Dirty);
-                    }
                 }
             }
         }
@@ -251,19 +247,28 @@ namespace Avalonia.Rendering.SceneGraph
 
             dirty.Remove(node.LayerRoot);
 
-            SetLayer(node, newLayerRoot);
+            SetLayer(node, newLayerRoot, dirty);
         }
 
-        private static void SetLayer(VisualNode node, IVisual layerRoot)
+        private static void SetLayer(VisualNode node, IVisual layerRoot, LayerDirtyRects dirty)
         {
+            if (node.LayerRoot == layerRoot)
+            {
+                throw new AvaloniaInternalException("Called SetLayer with unchanged LayerRoot.");
+            }
+
+            var oldLayerRoot = node.LayerRoot;
+
             node.LayerRoot = layerRoot;
+            dirty.Add(oldLayerRoot, node.Bounds);
+            dirty.Add(layerRoot, node.Bounds);
 
             foreach (VisualNode child in node.Children)
             {
                 // If the child is not the start of a new layer, recurse.
                 if (child.LayerRoot != child.Visual)
                 {
-                    SetLayer(child, layerRoot);
+                    SetLayer(child, layerRoot, dirty);
                 }
             }
         }

src/Avalonia.Visuals/Rendering/SceneGraph/VisualNode.cs

@@ -220,12 +220,13 @@ namespace Avalonia.Rendering.SceneGraph
         /// <inheritdoc/>
         public void BeginRender(IDrawingContextImpl context)
         {
-            context.Transform = Transform;
-
             if (ClipToBounds)
             {
-                context.PushClip(ClipBounds * Transform.Invert());
+                context.Transform = Matrix.Identity;
+                context.PushClip(ClipBounds);
             }
+
+            context.Transform = Transform;
         }
 
         /// <inheritdoc/>

tests/Avalonia.Visuals.UnitTests/Rendering/SceneGraph/SceneBuilderTests.cs

@@ -571,9 +571,13 @@ namespace Avalonia.Visuals.UnitTests.Rendering.SceneGraph
                 Assert.Same(tree, borderNode.LayerRoot);
                 Assert.Same(tree, canvasNode.LayerRoot);
 
-                Assert.Equal(1, dirty.Count());
-                Assert.Equal(tree, dirty.Single().Key);
-                Assert.Equal(new Rect(21, 21, 58, 78), dirty.Single().Value.Single());
+                var rootDirty = dirty[tree];
+                var borderDirty = dirty[border];
+
+                Assert.Equal(1, rootDirty.Count());
+                Assert.Equal(1, borderDirty.Count());
+                Assert.Equal(new Rect(21, 21, 58, 78), rootDirty.Single());
+                Assert.Equal(new Rect(21, 21, 58, 78), borderDirty.Single());
             }
         }