Add new tests for RadialGradient with GradientOffset handling. Fix implementation of Skia renderer to match Direct2d version.

src/Skia/Avalonia.Skia/DrawingContextImpl.cs

@@ -583,13 +583,13 @@ namespace Avalonia.Skia
                     var center = radialGradient.Center.ToPixels(targetSize).ToSKPoint();
                     var radius = (float)(radialGradient.Radius * targetSize.Width);
 
-                    // TODO: There is no SetAlpha in SkiaSharp
-                    //paint.setAlpha(128);
+                    var origin = radialGradient.GradientOrigin.ToPixels(targetSize).ToSKPoint();
 
                     // would be nice to cache these shaders possibly?
-                    using (var shader =
-                        SKShader.CreateRadialGradient(center, radius, stopColors, stopOffsets, tileMode))
-                    {
+                    using (var shader = SKShader.CreateCompose(
+                        SKShader.CreateColor(stopColors.Last()),
+                        SKShader.CreateTwoPointConicalGradient(center, radius, origin, 0, stopColors.Reverse().ToArray(), stopOffsets, tileMode))
+                    ) {
                         paintWrapper.Paint.Shader = shader;
                     }
 

tests/Avalonia.RenderTests/Media/RadialGradientBrushTests.cs

@@ -18,7 +18,7 @@ namespace Avalonia.Direct2D1.RenderTests.Media
         public RadialGradientBrushTests() : base(@"Media\RadialGradientBrush")
         {
         }
-        
+
         [Fact]
         public async Task RadialGradientBrush_RedBlue()
         {
@@ -43,5 +43,111 @@ namespace Avalonia.Direct2D1.RenderTests.Media
             await RenderToFile(target);
             CompareImages();
         }
+
+        [Fact]
+        public async Task RadialGradientBrush_RedBlue_Offset_Inside()
+        {
+            Decorator target = new Decorator
+            {
+                Padding = new Thickness(8),
+                Width = 200,
+                Height = 200,
+                Child = new Border
+                {
+                    Background = new RadialGradientBrush
+                    {
+                        GradientStops =
+                        {
+                            new GradientStop { Color = Colors.Red, Offset = 0 },
+                            new GradientStop { Color = Colors.Blue, Offset = 1 }
+                        },
+                        GradientOrigin = new RelativePoint(0.25, 0.25, RelativeUnit.Relative)
+                    }
+                }
+            };
+
+            await RenderToFile(target);
+            CompareImages();
+        }
+
+        [Fact]
+        public async Task RadialGradientBrush_RedBlue_Offset_Outside()
+        {
+            Decorator target = new Decorator
+            {
+                Padding = new Thickness(8),
+                Width = 200,
+                Height = 200,
+                Child = new Border
+                {
+                    Background = new RadialGradientBrush
+                    {
+                        GradientStops =
+                        {
+                            new GradientStop { Color = Colors.Red, Offset = 0 },
+                            new GradientStop { Color = Colors.Blue, Offset = 1 }
+                        },
+                        GradientOrigin = new RelativePoint(0.1, 0.1, RelativeUnit.Relative)
+                    }
+                }
+            };
+
+            await RenderToFile(target);
+            CompareImages();
+        }
+
+        [Fact]
+        public async Task RadialGradientBrush_RedGreenBlue_Offset_Inside()
+        {
+            Decorator target = new Decorator
+            {
+                Padding = new Thickness(8),
+                Width = 200,
+                Height = 200,
+                Child = new Border
+                {
+                    Background = new RadialGradientBrush
+                    {
+                        GradientStops =
+                        {
+                            new GradientStop { Color = Colors.Red, Offset = 0 },
+                            new GradientStop { Color = Colors.Green, Offset = 0.5 },
+                            new GradientStop { Color = Colors.Blue, Offset = 1 }
+                        },
+                        GradientOrigin = new RelativePoint(0.25, 0.25, RelativeUnit.Relative)
+                    }
+                }
+            };
+
+            await RenderToFile(target);
+            CompareImages();
+        }
+
+        [Fact]
+        public async Task RadialGradientBrush_RedGreenBlue_Offset_Outside()
+        {
+            Decorator target = new Decorator
+            {
+                Padding = new Thickness(8),
+                Width = 200,
+                Height = 200,
+                Child = new Border
+                {
+                    Background = new RadialGradientBrush
+                    {
+                        GradientStops =
+                        {
+                            new GradientStop { Color = Colors.Red, Offset = 0 },
+                            new GradientStop { Color = Colors.Green, Offset = 0.5 },
+                            new GradientStop { Color = Colors.Blue, Offset = 1 }
+                        },
+                        GradientOrigin = new RelativePoint(0.1, 0.1, RelativeUnit.Relative)
+                    }
+                }
+            };
+
+            await RenderToFile(target);
+            CompareImages();
+        }
     }
 }