feat(composition): Implement CrossFadeEffect + Sample

src/SamplesApp/UITests.Shared/Windows_UI_Composition/EffectBrushTests.xaml

@@ -22,5 +22,6 @@
 		<Grid x:Name="opacityGrid" Width="200" Height="200" VerticalAlignment="Top" HorizontalAlignment="Left" ToolTipService.ToolTip="OpacityEffect"/>
 		<Grid x:Name="contrastGrid" Width="200" Height="200" VerticalAlignment="Top" HorizontalAlignment="Left" ToolTipService.ToolTip="ContrastEffect"/>
 		<Grid x:Name="exposureGrid" Width="200" Height="200" VerticalAlignment="Top" HorizontalAlignment="Left" ToolTipService.ToolTip="ExposureEffect (Negative Value, -1)"/>
+		<Grid x:Name="crossfadeGrid" Width="200" Height="200" VerticalAlignment="Top" HorizontalAlignment="Left" ToolTipService.ToolTip="CrossFadeEffect"/>
 	</GridView>
 </UserControl>

src/SamplesApp/UITests.Shared/Windows_UI_Composition/EffectBrushTests.xaml.cs

@@ -124,6 +124,21 @@ private void EffectBrushTests_Loaded(object sender, RoutedEventArgs e)
 			var effectBrush12 = factory12.CreateBrush();
 
 			exposureGrid.Background = new EffectTesterBrush(effectBrush12);
+
+			var surface2 = LoadedImageSurface.StartLoadFromUri(new Uri("https://user-images.githubusercontent.com/34550324/266135095-71c9ce0a-4e49-408f-b2ff-670a53adef10.png"));
+			surface2.LoadCompleted += (s, o) =>
+			{
+				if (o.Status == LoadedImageSourceLoadStatus.Success)
+				{
+					var brush = compositor.CreateSurfaceBrush(surface2);
+
+					var effect13 = new SimpleCrossfadeEffect() { Source1 = new CompositionEffectSourceParameter("sourceBrush"), Source2 = new CompositionEffectSourceParameter("secondaryBrush"), CrossFade = 0.5f };
+					var factory13 = compositor.CreateEffectFactory(effect13);
+					var effectBrush13 = factory13.CreateBrush();
+
+					crossfadeGrid.Background = new EffectTesterBrushWithSecondaryBrush(effectBrush13, brush);
+				}
+			};
 #endif
 		}
 
@@ -731,6 +746,63 @@ public object GetProperty(uint index)
 			public IGraphicsEffectSource GetSource(uint index) => Source;
 			public uint GetSourceCount() => 1;
 		}
+
+		[Guid("12F575E8-4DB1-485F-9A84-03A07DD3829F")]
+		private class SimpleCrossfadeEffect : IGraphicsEffect, IGraphicsEffectSource, IGraphicsEffectD2D1Interop
+		{
+			private string _name = "SimpleCrossfadeEffect";
+			private Guid _id = new Guid("12F575E8-4DB1-485F-9A84-03A07DD3829F");
+
+			public string Name
+			{
+				get => _name;
+				set => _name = value;
+			}
+
+			public float CrossFade { get; set; } = 0.5f;
+
+			public IGraphicsEffectSource Source1 { get; set; }
+
+			public IGraphicsEffectSource Source2 { get; set; }
+
+			public Guid GetEffectId() => _id;
+
+			public void GetNamedPropertyMapping(string name, out uint index, out GraphicsEffectPropertyMapping mapping)
+			{
+				switch (name)
+				{
+					case "Weight":
+					case "CrossFade":
+					case "Crossfade":
+						{
+							index = 0;
+							mapping = GraphicsEffectPropertyMapping.Direct;
+							break;
+						}
+					default:
+						{
+							index = 0xFF;
+							mapping = (GraphicsEffectPropertyMapping)0xFF;
+							break;
+						}
+				}
+			}
+
+			public object GetProperty(uint index)
+			{
+				switch (index)
+				{
+					case 0:
+						return CrossFade;
+					default:
+						return null;
+				}
+			}
+
+			public uint GetPropertyCount() => 1;
+			public IGraphicsEffectSource GetSource(uint index) => index is 0 ? Source1 : Source2;
+			public uint GetSourceCount() => 2;
+		}
 #endif
 	}
 }

src/Uno.UI.Composition/Composition/CompositionEffectBrush.skia.cs

@@ -241,6 +241,7 @@ half4 main()
 										if (skMode == (SKBlendMode)0xFF) // Unsupported mode
 											return null;
 
+										// We have to do this manually because SKImageFilter.CreateMerge(SKImageFilter, SKImageFilter, SKBlendMode, SKImageFilter.CropRect) is obsolete.
 										for (uint idx = 1; idx < effectInterop.GetSourceCount(); idx++)
 										{
 											SKImageFilter nextFilter = GenerateEffectFilter(effectInterop.GetSource(idx), bounds);
@@ -278,6 +279,7 @@ half4 main()
 										effectInterop.GetNamedPropertyMapping("Opacity", out uint opacityProp, out _);
 										float opacity = (float)effectInterop.GetProperty(opacityProp);
 
+
 										return SKImageFilter.CreateColorFilter(
 											SKColorFilter.CreateColorMatrix(
 												new float[] // Opacity Matrix
@@ -530,6 +532,69 @@ half4 main()
 										*/
 									}
 
+									return null;
+								}
+							case EffectType.CrossFadeEffect: // TODO: We should use SkColorFilters::Lerp instead once SkiaSharp includes it
+								{
+									if (effectInterop.GetSourceCount() == 2 && effectInterop.GetPropertyCount() == 1 && effectInterop.GetSource(0) is IGraphicsEffectSource sourceA && effectInterop.GetSource(1) is IGraphicsEffectSource sourceB)
+									{
+										SKImageFilter sourceFilter1 = GenerateEffectFilter(sourceB, bounds);
+										if (sourceFilter1 is null)
+											return null;
+
+										SKImageFilter sourceFilter2 = GenerateEffectFilter(sourceA, bounds);
+										if (sourceFilter2 is null)
+											return null;
+
+										effectInterop.GetNamedPropertyMapping("CrossFade", out uint crossfadeProp, out _);
+
+										float crossfade = (float)effectInterop.GetProperty(crossfadeProp);
+
+										if (crossfade <= 0.0f)
+											return sourceFilter1;
+										else if (crossfade >= 1.0f)
+											return sourceFilter2;
+
+										SKImageFilter fbFilter = SKImageFilter.CreateColorFilter(
+											SKColorFilter.CreateColorMatrix(
+												new float[]
+												{
+													crossfade, 0,         0,         0,         0,
+													0,         crossfade, 0,         0,         0,
+													0,         0,         crossfade, 0,         0,
+													0,         0,         0,         crossfade, 0
+												}),
+											sourceFilter2);
+
+										string shader = $@"
+											uniform shader input;
+											uniform half crossfade;
+
+											half4 main() 
+											{{
+												half4 inputColor = sample(input);
+												return inputColor - (inputColor * crossfade);
+											}}
+										";
+
+										SKRuntimeEffect runtimeEffect = SKRuntimeEffect.Create(shader, out string errors);
+										if (errors is not null)
+											return null;
+
+										SKRuntimeEffectUniforms uniforms = new(runtimeEffect)
+										{
+											{ "crossfade", crossfade }
+										};
+										SKRuntimeEffectChildren children = new(runtimeEffect)
+										{
+											{ "input", null }
+										};
+
+										SKImageFilter amafFilter = SKImageFilter.CreateColorFilter(runtimeEffect.ToColorFilter(uniforms, children), sourceFilter1);
+
+										return SKImageFilter.CreateBlendMode(SKBlendMode.Plus, fbFilter, amafFilter, new(bounds));
+									}
+
 									return null;
 								}
 							case EffectType.Unsupported: