fix: ImageBrush RenderTransform does not throw

Author: MartinZikmund

src/SamplesApp/UITests.Shared/Windows_UI_Xaml_Media/GradientBrushTests/GradientsPage.xaml

@@ -281,7 +281,7 @@
 					</Border.BorderBrush>
 				</Border>
 			</StackPanel>
-			<TextBlock FontSize="15">Linear Gradient as Border with relative transform</TextBlock>
+			<TextBlock FontSize="15">Linear Gradient as Border with relative transform / with single stop</TextBlock>
 			<StackPanel Orientation="Horizontal" Spacing="10">
 				<Border Width="100" Height="100" BorderThickness="40" CornerRadius="8">
 					<Border.BorderBrush>
@@ -296,6 +296,15 @@
 						</LinearGradientBrush>
 					</Border.BorderBrush>
 				</Border>
+				<Border Width="100" Height="100" BorderThickness="40" CornerRadius="8">
+					<Border.BorderBrush>
+						<LinearGradientBrush MappingMode="Absolute" StartPoint="0,0" EndPoint="0,40">
+							<LinearGradientBrush.GradientStops>
+								<GradientStop Color="Red" Offset="0.5" />
+							</LinearGradientBrush.GradientStops>
+						</LinearGradientBrush>
+					</Border.BorderBrush>
+				</Border>
 			</StackPanel>
 			<TextBlock FontSize="15">Text with Radial/Linear gradient as foreground brush (fallback=green)</TextBlock>
 			<StackPanel Orientation="Horizontal" Spacing="10">

src/SamplesApp/UITests.Shared/Windows_UI_Xaml_Media/ImageBrushTests/ImageBrushWithRotateTransform.xaml

@@ -20,7 +20,7 @@
 			<DataTemplate>
 				<Border Width="150" Height="200">
 					<Border.Background>
-						<ImageBrush ImageSource="http://homepages.cae.wisc.edu/~ece533/images/fruits.png"
+						<ImageBrush ImageSource="ms-appx:///Assets/ingredient2.png"
 									Stretch="UniformToFill">
 							<ImageBrush.RelativeTransform>
 								<RotateTransform Angle="45" CenterX=".5" CenterY=".5"/>
@@ -31,4 +31,4 @@
 			</DataTemplate>
 		</controls:SampleControl.SampleContent>
 	</controls:SampleControl>
-</UserControl>
+</UserControl>

src/SamplesApp/UITests.Shared/Windows_UI_Xaml_Media/ImageBrushTests/ImageBrushWithScaleTransform.xaml

@@ -21,7 +21,7 @@
 				<Grid>
 				<Border Width="150" Height="200">
 					<Border.Background>
-						<ImageBrush ImageSource="http://homepages.cae.wisc.edu/~ece533/images/fruits.png"
+							<ImageBrush ImageSource="ms-appx:///Assets/ingredient2.png"
 									Stretch="UniformToFill">
 							<ImageBrush.RelativeTransform>
 								<ScaleTransform ScaleX="1.5" ScaleY="1.5" CenterX=".5" CenterY=".5"/>
@@ -33,4 +33,4 @@
 			</DataTemplate>
 		</controls:SampleControl.SampleContent>
 	</controls:SampleControl>
-</UserControl>
+</UserControl>

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

@@ -225,7 +225,7 @@ private Android.Graphics.Matrix GenerateMatrix(Windows.Foundation.Rect drawRect,
 
 			matrix.SetRectToRect(sourceRect.ToRectF(), destinationRect.ToRectF(), Android.Graphics.Matrix.ScaleToFit.Fill);
 
-			RelativeTransform?.ToNativeMatrix(matrix, size: new Size(drawRect.Width, drawRect.Height));
+			RelativeTransform?.ToNativeMatrix(matrix, size: new Size(sourceRect.Width, sourceRect.Height));
 			return matrix;
 		}
 

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

@@ -10,48 +10,54 @@ public partial class LinearGradientBrush
 	{
 		protected internal override Shader GetShader(Rect destinationRect)
 		{
-			// Android LinearGradient requires two ore more stop points.
-			//TODO: If there is only one - we should use solid color brush here
-			if (GradientStops.Count >= 2)
+			if (GradientStops.Count == 0)
 			{
-				var colors = GradientStops.SelectToArray(s => ((Android.Graphics.Color)s.Color).ToArgb());
-				var locations = GradientStops.SelectToArray(s => (float)s.Offset);
+				return null;
+			}
 
-				var width = destinationRect.Width;
-				var height = destinationRect.Height;
+			var colors = GradientStops.SelectToList(s => ((Android.Graphics.Color)s.Color).ToArgb());
+			var locations = GradientStops.SelectToList(s => (float)s.Offset);
 
-				Android.Graphics.Matrix nativeTransformMatrix = null;
-				if (RelativeTransform != null)
-				{
-					var matrix = RelativeTransform.ToMatrix(Foundation.Point.Zero, new Windows.Foundation.Size(width, height));
-					matrix.M31 *= (float)width;
-					matrix.M32 *= (float)height;
-					nativeTransformMatrix = matrix.ToNative();
-				}
+			if (GradientStops.Count == 1)
+			{
+				// Android LinearGradient requires two ore more stop points.
+				// We work around this by duplicating the first gradient stop.
+				colors.Add(colors[0]);
+				locations.Add(locations[0]);
+			}
+
+			var width = destinationRect.Width;
+			var height = destinationRect.Height;
+
+			Android.Graphics.Matrix nativeTransformMatrix = null;
+			if (RelativeTransform != null)
+			{
+				var matrix = RelativeTransform.ToMatrix(Foundation.Point.Zero, new Windows.Foundation.Size(width, height));
+				matrix.M31 *= (float)width;
+				matrix.M32 *= (float)height;
+				nativeTransformMatrix = matrix.ToNative();
+			}
 
-				//Matrix .MapPoints takes an array of floats
-				var pts = MappingMode == BrushMappingMode.RelativeToBoundingBox
-					? new[]
-					{
+			//Matrix .MapPoints takes an array of floats
+			var pts = MappingMode == BrushMappingMode.RelativeToBoundingBox
+				? new[]
+				{
 						(float) (StartPoint.X * width),
 						(float) (StartPoint.Y * height),
 						(float) (EndPoint.X * width),
 						(float) (EndPoint.Y * height)
-					}
-					: new[]
-					{
+				}
+				: new[]
+				{
 						(float) ViewHelper.LogicalToPhysicalPixels(StartPoint.X),
 						(float) ViewHelper.LogicalToPhysicalPixels(StartPoint.Y),
 						(float) ViewHelper.LogicalToPhysicalPixels(EndPoint.X),
 						(float) ViewHelper.LogicalToPhysicalPixels(EndPoint.Y)
-					};
-
-				nativeTransformMatrix?.MapPoints(pts);
-				nativeTransformMatrix?.Dispose();
-				return new LinearGradient(pts[0], pts[1], pts[2], pts[3], colors, locations, Shader.TileMode.Clamp);
-			}
+				};
 
-			return null;
+			nativeTransformMatrix?.MapPoints(pts);
+			nativeTransformMatrix?.Dispose();
+			return new LinearGradient(pts[0], pts[1], pts[2], pts[3], colors.ToArray(), locations.ToArray(), Shader.TileMode.Clamp);
 		}
 	}
 }

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

@@ -23,8 +23,8 @@ public partial class Transform
 
 			targetMatrix.SetValues(new[]
 			{
-				matrix.M11, matrix.M21, matrix.M31,
-				matrix.M12, matrix.M22, matrix.M32,
+				matrix.M11, matrix.M21, matrix.M31 * (float)size.Width,
+				matrix.M12, matrix.M22, matrix.M32 * (float)size.Height,
 				0, 0, 1
 			});