fix(revealbrush): Use RevealBrush FallbackColor

When a RevealBrush is set, use its FallbackColor for Panel.Background and Border.Background, since the actual reveal effect is not implemented.

This fixes TreeView selection background not being displayed (because, surprise, it's using RevealBrush).

src/SamplesApp/SamplesApp.UITests/Windows_UI_Xaml_Media/RevealBrushTests/RevealBrush_Tests.cs

@@ -0,0 +1,53 @@
+using System;
+using System.Collections.Generic;
+using System.Drawing;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using NUnit.Framework;
+using SamplesApp.UITests.TestFramework;
+
+namespace SamplesApp.UITests.Windows_UI_Xaml_Media.RevealBrushTests
+{
+	[TestFixture]
+	class RevealBrush_Tests : SampleControlUITestBase
+	{
+		[Test]
+		[AutoRetry]
+		public void When_FallbackColor_Set()
+		{
+			Run("UITests.Windows_UI_Xaml_Media.BrushesTests.RevealBrush_Fallback");
+
+			_app.WaitForElement("StatusTextBlock");
+
+			var views = new[]
+			{
+				"RevealGrid",
+				"RevealGridCR",
+				"RevealBorder",
+				"RevealBorderCR",
+			};
+
+			using var initial = TakeScreenshot("Initial");
+			foreach (var view in views)
+			{
+				AssertHasColor(view, initial, Color.Orange);
+			}
+
+			_app.FastTap("ChangeColorButton");
+			_app.WaitForText("StatusTextBlock", "Color changed");
+
+			using var after = TakeScreenshot("After");
+			foreach (var view in views)
+			{
+				AssertHasColor(view, after, Color.ForestGreen);
+			}
+
+			void AssertHasColor(string view, ScreenshotInfo screenshot, Color expectedColor)
+			{
+				var rect = _app.GetPhysicalRect(view);
+				ImageAssert.HasColorAt(screenshot, rect.CenterX, rect.CenterY, expectedColor);
+			}
+		}
+	}
+}

src/SamplesApp/UITests.Shared/UITests.Shared.projitems

@@ -3413,6 +3413,10 @@
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
     </Page>
+    <Page Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Media\BrushesTests\RevealBrush_Fallback.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </Page>
     <Page Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Media\BrushesTests\SolidColorBrush_Color_Changed.xaml">
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
@@ -6074,6 +6078,9 @@
       <DependentUpon>Brushes_ImplicitConvert.xaml</DependentUpon>
     </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Media\BrushesTests\ColorPresenter.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Media\BrushesTests\RevealBrush_Fallback.xaml.cs">
+      <DependentUpon>RevealBrush_Fallback.xaml</DependentUpon>
+    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Media\BrushesTests\SolidColorBrush_Color_Changed.xaml.cs">
       <DependentUpon>SolidColorBrush_Color_Changed.xaml</DependentUpon>
     </Compile>

src/SamplesApp/UITests.Shared/Windows_UI_Xaml_Media/BrushesTests/RevealBrush_Fallback.xaml

@@ -0,0 +1,52 @@
+<UserControl x:Class="UITests.Windows_UI_Xaml_Media.BrushesTests.RevealBrush_Fallback"
+			 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+			 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+			 xmlns:local="using:UITests.Windows_UI_Xaml_Media.BrushesTests"
+			 xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+			 xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+			 mc:Ignorable="d"
+			 d:DesignHeight="300"
+			 d:DesignWidth="400">
+	<UserControl.Resources>
+		<RevealBackgroundBrush x:Name="OrangeCrush"
+							   Color="Orange"
+							   FallbackColor="Orange" />
+	</UserControl.Resources>
+
+	<StackPanel>
+		<Button x:Name="ChangeColorButton"
+				Content="Change color"
+				Click="ChangeColor" />
+		<TextBlock x:Name="StatusTextBlock"
+				   Text="Initial" />
+
+		<Grid Background="{StaticResource OrangeCrush}"
+			  x:Name="RevealGrid"
+			  Margin="10"
+			  Width="120"
+			  Height="55">
+		</Grid>
+		<Grid CornerRadius="10"
+			  Background="{StaticResource OrangeCrush}"
+			  x:Name="RevealGridCR"
+			  Margin="10"
+			  Width="120"
+			  Height="55">
+		</Grid>
+
+		<Border Background="{StaticResource OrangeCrush}"
+				x:Name="RevealBorder"
+				Margin="10"
+				Width="120"
+				Height="55">
+		</Border>
+		<Border CornerRadius="10"
+				Background="{StaticResource OrangeCrush}"
+				x:Name="RevealBorderCR"
+				Margin="10"
+				Width="120"
+				Height="55">
+		</Border>
+
+	</StackPanel>
+</UserControl>

src/SamplesApp/UITests.Shared/Windows_UI_Xaml_Media/BrushesTests/RevealBrush_Fallback.xaml.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices.WindowsRuntime;
+using Uno.UI.Samples.Controls;
+using Windows.Foundation;
+using Windows.Foundation.Collections;
+using Windows.UI;
+using Windows.UI.Xaml;
+using Windows.UI.Xaml.Controls;
+using Windows.UI.Xaml.Controls.Primitives;
+using Windows.UI.Xaml.Data;
+using Windows.UI.Xaml.Input;
+using Windows.UI.Xaml.Media;
+using Windows.UI.Xaml.Navigation;
+
+// The User Control item template is documented at https://go.microsoft.com/fwlink/?LinkId=234236
+
+namespace UITests.Windows_UI_Xaml_Media.BrushesTests
+{
+	[Sample]
+	public sealed partial class RevealBrush_Fallback : UserControl
+	{
+		public RevealBrush_Fallback()
+		{
+			this.InitializeComponent();
+		}
+
+		private void ChangeColor(object sender, object args)
+		{
+			OrangeCrush.Color = Colors.ForestGreen;
+			OrangeCrush.FallbackColor = Colors.ForestGreen;
+			StatusTextBlock.Text = "Color changed";
+		}
+	}
+}

src/Uno.UI/UI/Xaml/Controls/Border/BorderLayerRenderer.Android.cs

@@ -459,6 +459,7 @@ private class LayoutState : IEquatable<LayoutState>
 			public readonly Thickness BorderThickness;
 			public readonly CornerRadius CornerRadius;
 			public readonly Thickness Padding;
+			public readonly Color? BackgroundFallbackColor;
 
 			public LayoutState(Windows.Foundation.Rect area, Brush background, Thickness borderThickness, Brush borderBrush, CornerRadius cornerRadius, Thickness padding)
 			{
@@ -474,6 +475,8 @@ public LayoutState(Windows.Foundation.Rect area, Brush background, Thickness bor
 
 				BackgroundColor = (Background as SolidColorBrush)?.Color;
 				BorderBrushColor = (BorderBrush as SolidColorBrush)?.Color;
+
+				BackgroundFallbackColor = (Background as XamlCompositionBrushBase)?.FallbackColor;
 			}
 
 			public bool Equals(LayoutState other)
@@ -487,7 +490,8 @@ public bool Equals(LayoutState other)
 					&& other.BorderBrushColor == BorderBrushColor
 					&& other.BorderThickness == BorderThickness
 					&& other.CornerRadius == CornerRadius
-					&& other.Padding == Padding;
+					&& other.Padding == Padding
+					&& other.BackgroundFallbackColor == BackgroundFallbackColor;
 			}
 		}
 	}

src/Uno.UI/UI/Xaml/Controls/Border/BorderLayerRenderer.iOSmacOS.cs

@@ -185,6 +185,11 @@ private static IDisposable InnerCreateLayer(UIElement owner, CALayer parent, Lay
 					acrylicBrush.Subscribe(owner, area, adjustedArea, parent, sublayers, ref insertionIndex, fillMask)
 						.DisposeWith(disposables);
 				}
+				else if (background is XamlCompositionBrushBase unsupportedCompositionBrush)
+				{
+					Brush.AssignAndObserveBrush(unsupportedCompositionBrush, color => innerLayer.FillColor = color)
+						.DisposeWith(disposables);
+				}
 				else
 				{
 					innerLayer.FillColor = Colors.Transparent;
@@ -268,6 +273,16 @@ private static IDisposable InnerCreateLayer(UIElement owner, CALayer parent, Lay
 
 					acrylicBrush.Subscribe(owner, fullArea, insideArea, parent, sublayers, ref insertionIndex, fillMask: null);
 				}
+				else if (background is XamlCompositionBrushBase unsupportedCompositionBrush)
+				{
+					Brush.AssignAndObserveBrush(unsupportedCompositionBrush, color => parent.BackgroundColor = color)
+						.DisposeWith(disposables);
+
+					// This is required because changing the CornerRadius changes the background drawing 
+					// implementation and we don't want a rectangular background behind a rounded background.
+					Disposable.Create(() => parent.BackgroundColor = null)
+						.DisposeWith(disposables);
+				}
 				else
 				{
 					parent.BackgroundColor = Colors.Transparent;

src/Uno.UI/UI/Xaml/Controls/Border/BorderLayerRenderer.skia.cs

@@ -148,6 +148,11 @@ private static IDisposable InnerCreateLayer(UIElement owner, LayoutState state)
 					Brush.AssignAndObserveBrush(acrylicBrush, color => backgroundShape.FillBrush = compositor.CreateColorBrush(color))
 						.DisposeWith(disposables);
 				}
+				else if (background is XamlCompositionBrushBase unsupportedCompositionBrush)
+				{
+					Brush.AssignAndObserveBrush(unsupportedCompositionBrush, color => backgroundShape.FillBrush = compositor.CreateColorBrush(color))
+						.DisposeWith(disposables);
+				}
 				else
 				{
 					backgroundShape.FillBrush = null;
@@ -220,6 +225,16 @@ private static IDisposable InnerCreateLayer(UIElement owner, LayoutState state)
 					Disposable.Create(() => backgroundShape.FillBrush = null)
 						.DisposeWith(disposables);
 				}
+				else if (background is XamlCompositionBrushBase unsupportedCompositionBrush)
+				{
+					Brush.AssignAndObserveBrush(unsupportedCompositionBrush, c => backgroundShape.FillBrush = compositor.CreateColorBrush(c))
+						.DisposeWith(disposables);
+
+					// This is required because changing the CornerRadius changes the background drawing 
+					// implementation and we don't want a rectangular background behind a rounded background.
+					Disposable.Create(() => backgroundShape.FillBrush = null)
+						.DisposeWith(disposables);
+				}
 				else
 				{
 					backgroundShape.FillBrush = null;

src/Uno.UI/UI/Xaml/FrameworkElement.Interface.wasm.cs

@@ -166,6 +166,11 @@ private void SetBackgroundBrush(Brush brush)
 					WindowManagerInterop.SetElementBackgroundGradient(HtmlId, gradientBrush.ToCssString(RenderSize));
 					RecalculateBrushOnSizeChanged(true);
 					break;
+				case XamlCompositionBrushBase unsupportedCompositionBrush:
+					var fallbackColor = unsupportedCompositionBrush.FallbackColorWithOpacity;
+					WindowManagerInterop.SetElementBackgroundColor(HtmlId, fallbackColor);
+					RecalculateBrushOnSizeChanged(false);
+					break;
 				default:
 					WindowManagerInterop.ResetElementBackground(HtmlId);
 					RecalculateBrushOnSizeChanged(false);

src/Uno.UI/UI/Xaml/Media/Brush.Android.cs

@@ -129,6 +129,24 @@ internal static IDisposable AssignAndObserveBrush(Brush b, ColorSetterHandler co
 
 				return disposables;
 			}
+			else if (b is XamlCompositionBrushBase unsupportedCompositionBrush)
+			{
+				var disposables = new CompositeDisposable(2);
+
+				colorSetter(unsupportedCompositionBrush.FallbackColorWithOpacity);
+
+				unsupportedCompositionBrush.RegisterDisposablePropertyChangedCallback(
+					XamlCompositionBrushBase.FallbackColorProperty,
+					(s, args) => colorSetter((s as XamlCompositionBrushBase).FallbackColorWithOpacity))
+					.DisposeWith(disposables);
+
+				unsupportedCompositionBrush.RegisterDisposablePropertyChangedCallback(
+					OpacityProperty,
+					(s, args) => colorSetter((s as XamlCompositionBrushBase).FallbackColorWithOpacity))
+					.DisposeWith(disposables);
+
+				return disposables;
+			}
 			else
 			{
 				colorSetter(SolidColorBrushHelper.Transparent.Color);

src/Uno.UI/UI/Xaml/Media/Brush.Skia.cs

@@ -57,6 +57,22 @@ internal static IDisposable AssignAndObserveBrush(Brush b, ColorSetterHandler co
 
 					return disposables;
 				}
+				else if (b is XamlCompositionBrushBase unsupportedCompositionBrush)
+				{
+					colorSetter(unsupportedCompositionBrush.FallbackColorWithOpacity);
+
+					unsupportedCompositionBrush.RegisterDisposablePropertyChangedCallback(
+						XamlCompositionBrushBase.FallbackColorProperty,
+						(s, colorArg) => colorSetter((s as XamlCompositionBrushBase).FallbackColorWithOpacity)
+					)
+					.DisposeWith(disposables);
+
+					unsupportedCompositionBrush.RegisterDisposablePropertyChangedCallback(
+						OpacityProperty,
+						(s, colorArg) => colorSetter((s as XamlCompositionBrushBase).FallbackColorWithOpacity)
+					)
+					.DisposeWith(disposables);
+				}
 				else
 				{
 					colorSetter(SolidColorBrushHelper.Transparent.Color);

src/Uno.UI/UI/Xaml/Media/Brush.iOSmacOS.cs

@@ -109,6 +109,25 @@ internal static IDisposable AssignAndObserveBrush(Brush b, ColorSetterHandler co
 
 				return disposables;
 			}
+			else if (b is XamlCompositionBrushBase unsupportedCompositionBrush)
+			{
+				var disposables = new CompositeDisposable(2);
+				colorSetter(unsupportedCompositionBrush.FallbackColorWithOpacity);
+
+				unsupportedCompositionBrush.RegisterDisposablePropertyChangedCallback(
+						XamlCompositionBrushBase.FallbackColorProperty,
+						(s, colorArg) => colorSetter((s as XamlCompositionBrushBase).FallbackColorWithOpacity)
+					)
+					.DisposeWith(disposables);
+
+				unsupportedCompositionBrush.RegisterDisposablePropertyChangedCallback(
+						OpacityProperty,
+						(s, colorArg) => colorSetter((s as XamlCompositionBrushBase).FallbackColorWithOpacity)
+					)
+					.DisposeWith(disposables);
+
+				return disposables;
+			}
 			else
 			{
 				colorSetter(SolidColorBrushHelper.Transparent.Color);

src/Uno.UI/UI/Xaml/Media/Brush.wasm.cs

@@ -76,6 +76,27 @@ internal static IDisposable AssignAndObserveBrush(Brush b, ColorSetterHandler co
 				return Disposable.Empty;
 			}
 
+			if (b is XamlCompositionBrushBase unsupportedCompositionBrush)
+			{
+				// 
+				var disposables = new CompositeDisposable(2);
+				colorSetter(unsupportedCompositionBrush.FallbackColorWithOpacity);
+
+				unsupportedCompositionBrush.RegisterDisposablePropertyChangedCallback(
+						XamlCompositionBrushBase.FallbackColorProperty,
+						(s, colorArg) => colorSetter((s as XamlCompositionBrushBase).FallbackColorWithOpacity)
+					)
+					.DisposeWith(disposables);
+
+				unsupportedCompositionBrush.RegisterDisposablePropertyChangedCallback(
+						OpacityProperty,
+						(s, colorArg) => colorSetter((s as XamlCompositionBrushBase).FallbackColorWithOpacity)
+					)
+					.DisposeWith(disposables);
+
+				return disposables;
+			}
+
 			colorSetter(SolidColorBrushHelper.Transparent.Color);
 			return Disposable.Empty;
 		}