Enable VisualBrush to be used as Visual's OpacityMask (#17072)

* Enable VisualBrush to be used as Visual's OpacityMask

* Add missing test file

---------

Co-authored-by: Benedikt Stebner <Gillibald@users.noreply.github.com>

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

@@ -1,6 +1,7 @@
 using System;
 using System.Numerics;
 using Avalonia.Media;
+using Avalonia.Rendering.Composition.Drawing;
 using Avalonia.VisualTree;
 
 namespace Avalonia.Rendering.Composition
@@ -25,9 +26,25 @@ namespace Avalonia.Rendering.Composition
             get => _opacityMask;
             set
             {
-                if (_opacityMask == value)
+                if (ReferenceEquals(_opacityMask, value))
                     return;
-                OpacityMaskBrush = (_opacityMask = value)?.ToImmutable();
+                
+                // Release the previous compositor-resource based brush
+                if (_opacityMask is ICompositionRenderResource<IBrush> oldCompositorBrush)
+                {
+                    oldCompositorBrush.ReleaseOnCompositor(Compositor);
+                    _opacityMask = null;
+                    OpacityMaskBrushTransportField = null;
+                }
+
+                if (value is ICompositionRenderResource<IBrush> newCompositorBrush)
+                {
+                    newCompositorBrush.AddRefOnCompositor(Compositor);
+                    OpacityMaskBrushTransportField = newCompositorBrush.GetForCompositor(Compositor);
+                    _opacityMask = value;
+                }
+                else
+                    OpacityMaskBrushTransportField = (_opacityMask = value)?.ToImmutable();
             }
         }
 

src/Avalonia.Base/Visual.Composition.cs

@@ -35,6 +35,7 @@ public partial class Visual
                 CompositionVisual.Children.Remove(ChildCompositionVisual);
                 
             CompositionVisual.DrawList = null;
+            CompositionVisual.OpacityMask = null;
             CompositionVisual = null;
         }
     }
@@ -141,7 +142,7 @@ public partial class Visual
         comp.Clip = Clip?.PlatformImpl;
         
         if (!Equals(comp.OpacityMask, OpacityMask))
-            comp.OpacityMask = OpacityMask?.ToImmutable();
+            comp.OpacityMask = OpacityMask;
 
         if (!comp.Effect.EffectEquals(Effect))
             comp.Effect = Effect?.ToImmutable();

src/Avalonia.Base/composition-schema.xml

@@ -31,7 +31,7 @@
         <Property Name="TransformMatrix" Type="Avalonia.Matrix" DefaultValue="Avalonia.Matrix.Identity" Animated="true" Internal="true"/>
         <Property Name="AdornedVisual" Type="CompositionVisual?" Internal="true" />
         <Property Name="AdornerIsClipped" Type="bool" Internal="true" />
-        <Property Name="OpacityMaskBrush" Type="Avalonia.Media.IImmutableBrush?" Internal="true" />
+        <Property Name="OpacityMaskBrush" ClientName="OpacityMaskBrushTransportField" Type="Avalonia.Media.IBrush?" Private="true"  />
         <Property Name="Effect" Type="Avalonia.Media.IImmutableEffect?" Internal="true" />
         <Property Name="RenderOptions" Type="Avalonia.Media.RenderOptions" />
     </Object>

src/tools/DevGenerators/CompositionGenerator/Config.cs

@@ -107,6 +107,8 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
         [XmlAttribute]
         public string Name { get; set; }
         [XmlAttribute]
+        public string ClientName { get; set; }
+        [XmlAttribute]
         public string Type { get; set; }
         [XmlAttribute]
         public string DefaultValue { get; set; }
@@ -116,6 +118,8 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
         public bool InternalSet { get; set; }
         [XmlAttribute]
         public bool Internal { get; set; }
+        [XmlAttribute]
+        public bool Private { get; set; }
     }
 
     public class GAnimationType

src/tools/DevGenerators/CompositionGenerator/Generator.cs

@@ -310,8 +310,9 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
             var fieldName = PropertyBackingFieldName(prop);
             return client
                     .AddMembers(DeclareField(prop.Type, fieldName))
-                    .AddMembers(PropertyDeclaration(propType, prop.Name)
-                        .AddModifiers(prop.Internal ? SyntaxKind.InternalKeyword : SyntaxKind.PublicKeyword)
+                    .AddMembers(PropertyDeclaration(propType, prop.ClientName ?? prop.Name)
+                        .AddModifiers(
+                            prop.Private ? SyntaxKind.PrivateKeyword : prop.Internal ? SyntaxKind.InternalKeyword : SyntaxKind.PublicKeyword)
                         .AddAccessorListAccessors(
                             AccessorDeclaration(SyntaxKind.GetAccessorDeclaration,
                                 Block(ReturnStatement(IdentifierName(fieldName)))),

tests/Avalonia.RenderTests/Media/VisualBrushTests.cs

@@ -710,5 +710,57 @@ namespace Avalonia.Direct2D1.RenderTests.Media
             await RenderToFile(new RelativePointTestPrimitivesHelper(brush), testName);
             CompareImages(testName);
         }
+        
+        
+        [Fact]
+        public async Task VisualBrush_Should_Be_Usable_As_Opacity_Mask()
+        {
+            var target = new Border()
+            {
+                Padding = new Thickness(8),
+                Width = 920,
+                Height = 920,
+                Background = Brushes.Magenta,
+                OpacityMask = new VisualBrush
+                {
+                    Stretch = Stretch.Fill,
+                    TileMode = TileMode.None,
+
+                    Visual = new Border()
+                    {
+                        Width = 200,
+                        Height = 200,
+                        Padding = new Thickness(20),
+                        Child = new Grid()
+                        {
+
+                            ColumnDefinitions = ColumnDefinitions.Parse("*,*,*"),
+                            RowDefinitions = RowDefinitions.Parse("*,*,*"),
+                            Children =
+                            {
+                                new Border()
+                                {
+                                    Background = Brushes.Aqua,
+                                },
+                                new Border()
+                                {
+                                    [Grid.ColumnProperty] = 1,
+                                    [Grid.RowProperty] = 2,
+                                    Background = Brushes.Aqua,
+                                },
+                                new Border()
+                                {
+                                    [Grid.ColumnProperty] = 3,
+                                    Background = Brushes.Aqua,
+                                },
+                            }
+                        },
+                    }
+                }
+            };
+
+            await RenderToFile(target);
+            CompareImages();
+        }
     }
 }