Added IAffectsRender interface...

...and use it as a general-purpose means of attaching to property values that can affect render.

src/Avalonia.Controls/Border.cs

@@ -43,9 +43,12 @@ namespace Avalonia.Controls
         /// </summary>
         static Border()
         {
-            AffectsRender<Border>(BorderThicknessProperty, CornerRadiusProperty);
+            AffectsRender<Border>(
+                BackgroundProperty,
+                BorderBrushProperty,
+                BorderThicknessProperty,
+                CornerRadiusProperty);
             AffectsMeasure<Border>(BorderThicknessProperty);
-            BrushAffectsRender<Border>(BackgroundProperty, BorderBrushProperty);
         }
 
         /// <summary>

src/Avalonia.Controls/Panel.cs

@@ -30,7 +30,7 @@ namespace Avalonia.Controls
         /// </summary>
         static Panel()
         {
-            BrushAffectsRender<Panel>(BackgroundProperty);
+            AffectsRender<Panel>(BackgroundProperty);
             ClipToBoundsProperty.OverrideDefaultValue<Panel>(true);
         }
 

src/Avalonia.Controls/Presenters/ContentPresenter.cs

@@ -90,9 +90,8 @@ namespace Avalonia.Controls.Presenters
         /// </summary>
         static ContentPresenter()
         {
-            AffectsRender<ContentPresenter>(BorderThicknessProperty, CornerRadiusProperty);
+            AffectsRender<ContentPresenter>(BackgroundProperty, BorderBrushProperty, BorderThicknessProperty, CornerRadiusProperty);
             AffectsMeasure<ContentPresenter>(BorderThicknessProperty, PaddingProperty);
-            BrushAffectsRender<ContentPresenter>(BackgroundProperty, BorderBrushProperty);
             ContentProperty.Changed.AddClassHandler<ContentPresenter>(x => x.ContentChanged);
             ContentTemplateProperty.Changed.AddClassHandler<ContentPresenter>(x => x.ContentChanged);
             TemplatedParentProperty.Changed.AddClassHandler<ContentPresenter>(x => x.TemplatedParentChanged);

src/Avalonia.Controls/Shapes/Shape.cs

@@ -33,8 +33,7 @@ namespace Avalonia.Controls.Shapes
         static Shape()
         {
             AffectsMeasure<Shape>(StretchProperty, StrokeThicknessProperty);
-            AffectsRender<Shape>(StrokeDashArrayProperty);
-            BrushAffectsRender<Shape>(FillProperty, StrokeProperty);
+            AffectsRender<Shape>(FillProperty, StrokeProperty, StrokeDashArrayProperty);
         }
 
         public Geometry DefiningGeometry

src/Avalonia.Controls/TextBlock.cs

@@ -101,10 +101,11 @@ namespace Avalonia.Controls
         {
             ClipToBoundsProperty.OverrideDefaultValue<TextBlock>(true);
             AffectsRender<TextBlock>(
+                BackgroundProperty,
+                ForegroundProperty,
                 FontWeightProperty,
                 FontSizeProperty,
                 FontStyleProperty);
-            BrushAffectsRender<TextBlock>(BackgroundProperty, ForegroundProperty);
         }
 
         /// <summary>

src/Avalonia.Visuals/Media/Brush.cs

@@ -19,7 +19,7 @@ namespace Avalonia.Media
             AvaloniaProperty.Register<Brush, double>(nameof(Opacity), 1.0);
 
         /// <inheritdoc/>
-        public event EventHandler Changed;
+        public event EventHandler Invalidated;
 
         /// <summary>
         /// Gets or sets the opacity of the brush.
@@ -63,14 +63,14 @@ namespace Avalonia.Media
         /// <param name="properties">The properties.</param>
         /// <remarks>
         /// After a call to this method in a brush's static constructor, any change to the
-        /// property will cause the <see cref="Changed"/> event to be raised on the brush.
+        /// property will cause the <see cref="Invalidated"/> event to be raised on the brush.
         /// </remarks>
         protected static void AffectsRender<T>(params AvaloniaProperty[] properties)
             where T : Brush
         {
             void Invalidate(AvaloniaPropertyChangedEventArgs e)
             {
-                (e.Sender as T)?.RaiseChanged(EventArgs.Empty);
+                (e.Sender as T)?.RaiseInvalidated(EventArgs.Empty);
             }
 
             foreach (var property in properties)
@@ -80,9 +80,9 @@ namespace Avalonia.Media
         }
 
         /// <summary>
-        /// Raises the <see cref="Changed"/> event.
+        /// Raises the <see cref="Invalidated"/> event.
         /// </summary>
         /// <param name="e">The event args.</param>
-        protected void RaiseChanged(EventArgs e) => Changed?.Invoke(this, e);
+        protected void RaiseInvalidated(EventArgs e) => Invalidated?.Invoke(this, e);
     }
 }

src/Avalonia.Visuals/Media/GradientBrush.cs

@@ -80,18 +80,18 @@ namespace Avalonia.Media
                     brush._gradientStopsSubscription = newValue.TrackItemPropertyChanged(brush.GradientStopChanged);
                 }
 
-                brush.RaiseChanged(EventArgs.Empty);
+                brush.RaiseInvalidated(EventArgs.Empty);
             }
         }
 
         private void GradientStopsChanged(object sender, NotifyCollectionChangedEventArgs e)
         {
-            RaiseChanged(EventArgs.Empty);
+            RaiseInvalidated(EventArgs.Empty);
         }
 
         private void GradientStopChanged(Tuple<object, PropertyChangedEventArgs> e)
         {
-            RaiseChanged(EventArgs.Empty);
+            RaiseInvalidated(EventArgs.Empty);
         }
     }
 }

src/Avalonia.Visuals/Media/IAffectsRender.cs

@@ -0,0 +1,16 @@
+using System;
+
+namespace Avalonia.Media
+{
+    /// <summary>
+    /// Signals to a self-rendering control that changes to the resource should invoke
+    /// <see cref="Visual.InvalidateVisual"/>.
+    /// </summary>
+    public interface IAffectsRender
+    {
+        /// <summary>
+        /// Raised when the resource changes visually.
+        /// </summary>
+        event EventHandler Invalidated;
+    }
+}

src/Avalonia.Visuals/Media/IMutableBrush.cs

@@ -5,13 +5,8 @@ namespace Avalonia.Media
     /// <summary>
     /// Represents a mutable brush which can return an immutable clone of itself.
     /// </summary>
-    public interface IMutableBrush : IBrush
+    public interface IMutableBrush : IBrush, IAffectsRender
     {
-        /// <summary>
-        /// Raised when the brush changes visually.
-        /// </summary>
-        event EventHandler Changed;
-
         /// <summary>
         /// Creates an immutable clone of the brush.
         /// </summary>

src/Avalonia.Visuals/Visual.cs

@@ -338,45 +338,20 @@ namespace Avalonia
         /// FrameworkPropertyMetadata.AffectsRender flag.
         /// </remarks>
         protected static void AffectsRender<T>(params AvaloniaProperty[] properties)
-            where T : class, IVisual
-        {
-            void Invalidate(AvaloniaPropertyChangedEventArgs e)
-            {
-                (e.Sender as T)?.InvalidateVisual();
-            }
-
-            foreach (var property in properties)
-            {
-                property.Changed.Subscribe(Invalidate);
-            }
-        }
-
-        /// <summary>
-        /// Indicates that a brush property change should cause <see cref="InvalidateVisual"/> to be
-        /// called.
-        /// </summary>
-        /// <param name="properties">The properties.</param>
-        /// <remarks>
-        /// This method should be called in a control's static constructor with each property
-        /// on the control which when changed should cause a redraw. It not only triggers an
-        /// invalidation when the property itself changes, but also when the brush raises
-        /// the <see cref="IMutableBrush.Changed"/> event.
-        /// </remarks>
-        protected static void BrushAffectsRender<T>(params AvaloniaProperty<IBrush>[] properties)
             where T : Visual
         {
             void Invalidate(AvaloniaPropertyChangedEventArgs e)
             {
                 if (e.Sender is T sender)
                 {
-                    if (e.OldValue is IMutableBrush oldValue)
+                    if (e.OldValue is IAffectsRender oldValue)
                     {
-                        oldValue.Changed -= sender.BrushChanged;
+                        oldValue.Invalidated -= sender.AffectsRenderInvalidated;
                     }
 
-                    if (e.NewValue is IMutableBrush newValue)
+                    if (e.NewValue is IAffectsRender newValue)
                     {
-                        newValue.Changed += sender.BrushChanged;
+                        newValue.Invalidated += sender.AffectsRenderInvalidated;
                     }
 
                     sender.InvalidateVisual();
@@ -582,7 +557,7 @@ namespace Avalonia
             OnVisualParentChanged(old, value);
         }
 
-        private void BrushChanged(object sender, EventArgs e) => InvalidateVisual();
+        private void AffectsRenderInvalidated(object sender, EventArgs e) => InvalidateVisual();
 
         /// <summary>
         /// Called when the <see cref="VisualChildren"/> collection changes.

tests/Avalonia.Visuals.UnitTests/Media/ImageBrushTests.cs

@@ -11,14 +11,14 @@ namespace Avalonia.Visuals.UnitTests.Media
     public class ImageBrushTests
     {
         [Fact]
-        public void Changing_Source_Raises_Changed()
+        public void Changing_Source_Raises_Invalidated()
         {
             var bitmap1 = Mock.Of<IBitmap>();
             var bitmap2 = Mock.Of<IBitmap>();
             var target = new ImageBrush(bitmap1);
             var raised = false;
 
-            target.Changed += (s, e) => raised = true;
+            target.Invalidated += (s, e) => raised = true;
             target.Source = bitmap2;
 
             Assert.True(raised);

tests/Avalonia.Visuals.UnitTests/Media/LinearGradientBrushTests.cs

@@ -9,7 +9,7 @@ namespace Avalonia.Visuals.UnitTests.Media
     public class LinearGradientBrushTests
     {
         [Fact]
-        public void Changing_StartPoint_Raises_Changed()
+        public void Changing_StartPoint_Raises_Invalidated()
         {
             var bitmap1 = Mock.Of<IBitmap>();
             var bitmap2 = Mock.Of<IBitmap>();
@@ -17,14 +17,14 @@ namespace Avalonia.Visuals.UnitTests.Media
             var raised = false;
 
             target.StartPoint = new RelativePoint();
-            target.Changed += (s, e) => raised = true;
+            target.Invalidated += (s, e) => raised = true;
             target.StartPoint = new RelativePoint(10, 10, RelativeUnit.Absolute);
 
             Assert.True(raised);
         }
 
         [Fact]
-        public void Changing_EndPoint_Raises_Changed()
+        public void Changing_EndPoint_Raises_Invalidated()
         {
             var bitmap1 = Mock.Of<IBitmap>();
             var bitmap2 = Mock.Of<IBitmap>();
@@ -32,14 +32,14 @@ namespace Avalonia.Visuals.UnitTests.Media
             var raised = false;
 
             target.EndPoint = new RelativePoint();
-            target.Changed += (s, e) => raised = true;
+            target.Invalidated += (s, e) => raised = true;
             target.EndPoint = new RelativePoint(10, 10, RelativeUnit.Absolute);
 
             Assert.True(raised);
         }
 
         [Fact]
-        public void Changing_GradientStops_Raises_Changed()
+        public void Changing_GradientStops_Raises_Invalidated()
         {
             var bitmap1 = Mock.Of<IBitmap>();
             var bitmap2 = Mock.Of<IBitmap>();
@@ -47,14 +47,14 @@ namespace Avalonia.Visuals.UnitTests.Media
             var raised = false;
 
             target.GradientStops = new GradientStops { new GradientStop(Colors.Red, 0) };
-            target.Changed += (s, e) => raised = true;
+            target.Invalidated += (s, e) => raised = true;
             target.GradientStops = new GradientStops { new GradientStop(Colors.Green, 0) };
 
             Assert.True(raised);
         }
 
         [Fact]
-        public void Adding_GradientStop_Raises_Changed()
+        public void Adding_GradientStop_Raises_Invalidated()
         {
             var bitmap1 = Mock.Of<IBitmap>();
             var bitmap2 = Mock.Of<IBitmap>();
@@ -62,14 +62,14 @@ namespace Avalonia.Visuals.UnitTests.Media
             var raised = false;
 
             target.GradientStops = new GradientStops { new GradientStop(Colors.Red, 0) };
-            target.Changed += (s, e) => raised = true;
+            target.Invalidated += (s, e) => raised = true;
             target.GradientStops.Add(new GradientStop(Colors.Green, 1));
 
             Assert.True(raised);
         }
 
         [Fact]
-        public void Changing_GradientStop_Offset_Raises_Changed()
+        public void Changing_GradientStop_Offset_Raises_Invalidated()
         {
             var bitmap1 = Mock.Of<IBitmap>();
             var bitmap2 = Mock.Of<IBitmap>();
@@ -77,7 +77,7 @@ namespace Avalonia.Visuals.UnitTests.Media
             var raised = false;
 
             target.GradientStops = new GradientStops { new GradientStop(Colors.Red, 0) };
-            target.Changed += (s, e) => raised = true;
+            target.Invalidated += (s, e) => raised = true;
             target.GradientStops[0].Offset = 0.5;
 
             Assert.True(raised);

tests/Avalonia.Visuals.UnitTests/Media/SolidColorBrushTests.cs

@@ -7,12 +7,12 @@ namespace Avalonia.Visuals.UnitTests.Media
     public class SolidColorBrushTests
     {
         [Fact]
-        public void Changing_Color_Raises_Changed()
+        public void Changing_Color_Raises_Invalidated()
         {
             var target = new SolidColorBrush(Colors.Red);
             var raised = false;
 
-            target.Changed += (s, e) => raised = true;
+            target.Invalidated += (s, e) => raised = true;
             target.Color = Colors.Green;
 
             Assert.True(raised);