[SKIA] UseOpacitySaveLayer feature switch (#9964)

* [SKIA] Introduce UseOpacitySaveLayer feature switch

* Only maintain _currentOpacity when OpacitySaveLayer is disabled

src/Avalonia.Base/Media/DrawingContext.cs

@@ -361,11 +361,12 @@ namespace Avalonia.Media
         /// Pushes an opacity value.
         /// </summary>
         /// <param name="opacity">The opacity.</param>
+        /// <param name="bounds">The bounds.</param>
         /// <returns>A disposable used to undo the opacity.</returns>
-        public PushedState PushOpacity(double opacity)
+        public PushedState PushOpacity(double opacity, Rect bounds)
         //TODO: Eliminate platform-specific push opacity call
         {
-            PlatformImpl.PushOpacity(opacity);
+            PlatformImpl.PushOpacity(opacity, bounds);
             return new PushedState(this, PushedState.PushedStateType.Opacity);
         }
 

src/Avalonia.Base/Media/DrawingGroup.cs

@@ -74,10 +74,12 @@ namespace Avalonia.Media
 
         public override void Draw(DrawingContext context)
         {
+            var bounds = GetBounds();
+
             using (context.PushPreTransform(Transform?.Value ?? Matrix.Identity))
-            using (context.PushOpacity(Opacity))
+            using (context.PushOpacity(Opacity, bounds))
             using (ClipGeometry != null ? context.PushGeometryClip(ClipGeometry) : default)
-            using (OpacityMask != null ? context.PushOpacityMask(OpacityMask, GetBounds()) : default)
+            using (OpacityMask != null ? context.PushOpacityMask(OpacityMask, bounds) : default)
             {
                 foreach (var drawing in Children)
                 {
@@ -284,7 +286,7 @@ namespace Avalonia.Media
                 throw new NotImplementedException();
             }
 
-            public void PushOpacity(double opacity)
+            public void PushOpacity(double opacity, Rect bounds)
             {
                 throw new NotImplementedException();
             }

src/Avalonia.Base/Media/ImmediateDrawingContext.cs

@@ -281,11 +281,12 @@ namespace Avalonia.Media
         /// Pushes an opacity value.
         /// </summary>
         /// <param name="opacity">The opacity.</param>
+        /// <param name="bounds">The bounds.</param>
         /// <returns>A disposable used to undo the opacity.</returns>
-        public PushedState PushOpacity(double opacity)
+        public PushedState PushOpacity(double opacity, Rect bounds)
         //TODO: Eliminate platform-specific push opacity call
         {
-            PlatformImpl.PushOpacity(opacity);
+            PlatformImpl.PushOpacity(opacity, bounds);
             return new PushedState(this, PushedState.PushedStateType.Opacity);
         }
 

src/Avalonia.Base/Platform/IDrawingContextImpl.cs

@@ -128,7 +128,7 @@ namespace Avalonia.Platform
         /// Pushes an opacity value.
         /// </summary>
         /// <param name="opacity">The opacity.</param>
-        void PushOpacity(double opacity);
+        void PushOpacity(double opacity, Rect bounds);
 
         /// <summary>
         /// Pops the latest pushed opacity value.

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

@@ -313,13 +313,13 @@ internal class CompositionDrawingContext : IDrawingContextImpl, IDrawingContextW
     }
 
     /// <inheritdoc/>
-    public void PushOpacity(double opacity)
+    public void PushOpacity(double opacity, Rect bounds)
     {
         var next = NextDrawAs<OpacityNode>();
 
-        if (next == null || !next.Item.Equals(opacity))
+        if (next == null || !next.Item.Equals(opacity, bounds))
         {
-            Add(new OpacityNode(opacity));
+            Add(new OpacityNode(opacity, bounds));
         }
         else
         {

src/Avalonia.Base/Rendering/Composition/Server/DrawingContextProxy.cs

@@ -111,9 +111,9 @@ internal class CompositorDrawingContextProxy : IDrawingContextImpl, IDrawingCont
         _impl.PopClip();
     }
 
-    public void PushOpacity(double opacity)
+    public void PushOpacity(double opacity, Rect bounds)
     {
-        _impl.PushOpacity(opacity);
+        _impl.PushOpacity(opacity, bounds);
     }
 
     public void PopOpacity()

src/Avalonia.Base/Rendering/Composition/Server/ServerCompositionVisual.cs

@@ -41,9 +41,9 @@ namespace Avalonia.Rendering.Composition.Server
                 return;
 
             Root!.RenderedVisuals++;
-            
-            if (Opacity != 1)
-                canvas.PushOpacity(Opacity);
+
+            var boundsRect = new Rect(new Size(Size.X, Size.Y));
+
             if (AdornedVisual != null)
             {
                 canvas.PostTransform = Matrix.Identity;
@@ -54,15 +54,16 @@ namespace Avalonia.Rendering.Composition.Server
             var transform = GlobalTransformMatrix;
             canvas.PostTransform = MatrixUtils.ToMatrix(transform);
             canvas.Transform = Matrix.Identity;
-            
-            var boundsRect = new Rect(new Size(Size.X, Size.Y));
+
+            if (Opacity != 1)
+                canvas.PushOpacity(Opacity, boundsRect);
             if (ClipToBounds && !HandlesClipToBounds)
                 canvas.PushClip(Root!.SnapToDevicePixels(boundsRect));
             if (Clip != null) 
                 canvas.PushGeometryClip(Clip);
             if(OpacityMaskBrush != null)
                 canvas.PushOpacityMask(OpacityMaskBrush, boundsRect);
-            
+
             RenderCore(canvas, currentTransformedClip);
             
             // Hack to force invalidation of SKMatrix

src/Avalonia.Base/Rendering/ImmediateRenderer.cs

@@ -117,7 +117,7 @@ namespace Avalonia.Rendering
                 }
 
                 using (context.PushPostTransform(m))
-                using (context.PushOpacity(opacity))
+                using (context.PushOpacity(opacity, bounds))
                 using (clipToBounds
 #pragma warning disable CS0618 // Type or member is obsolete
                     ? visual is IVisualWithRoundRectClip roundClipVisual

src/Avalonia.Base/Rendering/SceneGraph/OpacityNode.cs

@@ -12,9 +12,11 @@ namespace Avalonia.Rendering.SceneGraph
         /// opacity push.
         /// </summary>
         /// <param name="opacity">The opacity to push.</param>
-        public OpacityNode(double opacity)
+        /// <param name="bounds">The bounds.</param>
+        public OpacityNode(double opacity, Rect bounds)
         {
             Opacity = opacity;
+            Bounds = bounds;
         }
 
         /// <summary>
@@ -26,7 +28,7 @@ namespace Avalonia.Rendering.SceneGraph
         }
 
         /// <inheritdoc/>
-        public Rect Bounds => default;
+        public Rect Bounds { get; }
 
         /// <summary>
         /// Gets the opacity to be pushed or null if the operation represents a pop.
@@ -40,19 +42,20 @@ namespace Avalonia.Rendering.SceneGraph
         /// Determines if this draw operation equals another.
         /// </summary>
         /// <param name="opacity">The opacity of the other draw operation.</param>
+        /// <param name="bounds">The bounds of the other draw operation.</param>
         /// <returns>True if the draw operations are the same, otherwise false.</returns>
         /// <remarks>
         /// The properties of the other draw operation are passed in as arguments to prevent
         /// allocation of a not-yet-constructed draw operation object.
         /// </remarks>
-        public bool Equals(double? opacity) => Opacity == opacity;
+        public bool Equals(double? opacity, Rect bounds) => Opacity == opacity && Bounds == bounds;
 
         /// <inheritdoc/>
         public void Render(IDrawingContextImpl context)
         {
             if (Opacity.HasValue)
             {
-                context.PushOpacity(Opacity.Value);
+                context.PushOpacity(Opacity.Value, Bounds);
             }
             else
             {

src/Avalonia.Headless/HeadlessPlatformRenderInterface.cs

@@ -392,7 +392,7 @@ namespace Avalonia.Headless
 
             }
 
-            public void PushOpacity(double opacity)
+            public void PushOpacity(double opacity, Rect rect)
             {
 
             }

src/Skia/Avalonia.Skia/DrawingContextImpl.cs

@@ -40,6 +40,7 @@ namespace Avalonia.Skia
         private static SKShader? s_acrylicNoiseShader;
         private readonly ISkiaGpuRenderSession? _session;
         private bool _leased;
+        private bool _useOpacitySaveLayer;
 
         /// <summary>
         /// Context create info.
@@ -158,6 +159,13 @@ namespace Avalonia.Skia
             }
 
             Transform = Matrix.Identity;
+
+            var options = AvaloniaLocator.Current.GetService<SkiaOptions>();
+
+            if(options != null)
+            {
+                _useOpacitySaveLayer = options.UseOpacitySaveLayer;
+            }
         }
         
         /// <summary>
@@ -188,7 +196,7 @@ namespace Avalonia.Skia
             var d = destRect.ToSKRect();
 
             var paint = SKPaintCache.Shared.Get();
-            paint.Color = new SKColor(255, 255, 255, (byte)(255 * opacity * _currentOpacity));
+            paint.Color = new SKColor(255, 255, 255, (byte)(255 * opacity * (_useOpacitySaveLayer ? 1 : _currentOpacity)));
             paint.FilterQuality = bitmapInterpolationMode.ToSKFilterQuality();
             paint.BlendMode = _currentBlendingMode.ToSKBlendMode();
 
@@ -373,7 +381,7 @@ namespace Avalonia.Skia
             {
                 if (!boxShadow.IsDefault && !boxShadow.IsInset)
                 {
-                    using (var shadow = BoxShadowFilter.Create(_boxShadowPaint, boxShadow, _currentOpacity))
+                    using (var shadow = BoxShadowFilter.Create(_boxShadowPaint, boxShadow, _useOpacitySaveLayer ? 1 : _currentOpacity))
                     {
                         var spread = (float)boxShadow.Spread;
                         if (boxShadow.IsInset)
@@ -430,7 +438,7 @@ namespace Avalonia.Skia
             {
                 if (!boxShadow.IsDefault && boxShadow.IsInset)
                 {
-                    using (var shadow = BoxShadowFilter.Create(_boxShadowPaint, boxShadow, _currentOpacity))
+                    using (var shadow = BoxShadowFilter.Create(_boxShadowPaint, boxShadow, _useOpacitySaveLayer ? 1 : _currentOpacity))
                     {
                         var spread = (float)boxShadow.Spread;
                         var offsetX = (float)boxShadow.OffsetX;
@@ -568,18 +576,35 @@ namespace Avalonia.Skia
         }
 
         /// <inheritdoc />
-        public void PushOpacity(double opacity)
+        public void PushOpacity(double opacity, Rect bounds)
         {
             CheckLease();
-            _opacityStack.Push(_currentOpacity);
-            _currentOpacity *= opacity;
+
+            if(_useOpacitySaveLayer)
+            {
+                var rect = bounds.ToSKRect();
+                Canvas.SaveLayer(rect, new SKPaint { ColorF = new SKColorF(0, 0, 0, (float)opacity)});
+            }
+            else
+            {
+                _opacityStack.Push(_currentOpacity);
+                _currentOpacity *= opacity;
+            }
         }
 
         /// <inheritdoc />
         public void PopOpacity()
         {
             CheckLease();
-            _currentOpacity = _opacityStack.Pop();
+
+            if(_useOpacitySaveLayer)
+            {
+                Canvas.Restore();
+            }
+            else
+            {
+                _currentOpacity = _opacityStack.Pop();
+            }    
         }
 
         /// <inheritdoc />
@@ -657,7 +682,7 @@ namespace Avalonia.Skia
 
             var paint = SKPaintCache.Shared.Get();
 
-            Canvas.SaveLayer(paint);
+            Canvas.SaveLayer(bounds.ToSKRect(), paint);
             _maskStack.Push(CreatePaint(paint, mask, bounds.Size));
         }
 
@@ -1021,8 +1046,6 @@ namespace Avalonia.Skia
 
             paint.IsAntialias = true;
 
-            double opacity = _currentOpacity;
-
             var tintOpacity =
                 material.BackgroundSource == AcrylicBackgroundSource.Digger ?
                 material.TintOpacity : 1;
@@ -1071,7 +1094,7 @@ namespace Avalonia.Skia
 
             paint.IsAntialias = true;
 
-            double opacity = brush.Opacity * _currentOpacity;
+            double opacity = brush.Opacity * (_useOpacitySaveLayer ? 1 :_currentOpacity);
 
             if (brush is ISolidColorBrush solid)
             {

src/Skia/Avalonia.Skia/SkiaOptions.cs

@@ -16,5 +16,13 @@ namespace Avalonia
         /// Setting this to null will give you the default Skia value.
         /// </remarks>
         public long? MaxGpuResourceSizeBytes { get; set; } = 1024 * 600 * 4 * 12; // ~28mb 12x 1024 x 600 textures. 
+
+        /// <summary>
+        /// Use Skia's SaveLayer API to handling opacity.
+        /// </summary>
+        /// <remarks>
+        /// Enabling this might have performance implications.
+        /// </remarks>
+        public bool UseOpacitySaveLayer { get; set; } = false;
     }
 }

src/Windows/Avalonia.Direct2D1/Media/DrawingContextImpl.cs

@@ -441,14 +441,15 @@ namespace Avalonia.Direct2D1.Media
         /// Pushes an opacity value.
         /// </summary>
         /// <param name="opacity">The opacity.</param>
+        /// <param name="bounds">The bounds.</param>
         /// <returns>A disposable used to undo the opacity.</returns>
-        public void PushOpacity(double opacity)
+        public void PushOpacity(double opacity, Rect bounds)
         {
             if (opacity < 1)
             {
                 var parameters = new LayerParameters
                 {
-                    ContentBounds = PrimitiveExtensions.RectangleInfinite,
+                    ContentBounds = bounds.ToDirect2D(),
                     MaskTransform = PrimitiveExtensions.Matrix3x2Identity,
                     Opacity = (float)opacity,
                 };

tests/Avalonia.Benchmarks/NullDrawingContextImpl.cs

@@ -65,7 +65,7 @@ namespace Avalonia.Benchmarks
         {
         }
 
-        public void PushOpacity(double opacity)
+        public void PushOpacity(double opacity, Rect bounds)
         {
         }
 

tests/Avalonia.RenderTests/Controls/CustomRenderTests.cs

@@ -141,7 +141,7 @@ namespace Avalonia.Direct2D1.RenderTests.Controls
                         new Rect(control.Bounds.Size),
                         4);
 
-                    using (context.PushOpacity(0.5))
+                    using (context.PushOpacity(0.5, control.Bounds))
                     {
                         context.FillRectangle(
                             Brushes.Blue,

tests/Avalonia.RenderTests/Media/BitmapTests.cs

@@ -79,7 +79,7 @@ namespace Avalonia.Direct2D1.RenderTests.Media
             using (var ctx = target.CreateDrawingContext(null))
             {
                 ctx.Clear(Colors.Transparent);
-                ctx.PushOpacity(0.8);
+                ctx.PushOpacity(0.8, new Rect(0, 0, 80, 80));
                 ctx.DrawRectangle(Brushes.Chartreuse, null, new Rect(0, 0, 20, 100));
                 ctx.DrawRectangle(Brushes.Crimson, null, new Rect(20, 0, 20, 100));
                 ctx.DrawRectangle(Brushes.Gold,null, new Rect(40, 0, 20, 100));