From 9adbe33577402e24207dce89e81b5cfbf05771a9 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Mon, 6 Apr 2020 18:53:12 +0200
Subject: [PATCH 1/2] Added failing test for #2755.

---
 tests/Avalonia.Visuals.UnitTests/Media/BrushTests.cs | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/tests/Avalonia.Visuals.UnitTests/Media/BrushTests.cs b/tests/Avalonia.Visuals.UnitTests/Media/BrushTests.cs
index 1ef8f1f29a..1a2f7732dd 100644
--- a/tests/Avalonia.Visuals.UnitTests/Media/BrushTests.cs
+++ b/tests/Avalonia.Visuals.UnitTests/Media/BrushTests.cs
@@ -77,5 +77,17 @@ namespace Avalonia.Visuals.UnitTests.Media
         {
             Assert.Throws<FormatException>(() => Brush.Parse("#ff808g80"));
         }
+
+        [Fact]
+        public void Changing_Opacity_Raises_Invalidated()
+        {
+            var target = new SolidColorBrush();
+            var raised = false;
+
+            target.Invalidated += (s, e) => raised = true;
+            target.Opacity = 0.5;
+
+            Assert.True(raised);
+        }
     }
 }

From 3fc21f30b4b3ce57bee74832b9185b47bc8fbe2f Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Mon, 6 Apr 2020 18:55:27 +0200
Subject: [PATCH 2/2] Invalidate brush when Opacity changes.

Fixes #2755.
---
 src/Avalonia.Visuals/Media/Brush.cs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/Avalonia.Visuals/Media/Brush.cs b/src/Avalonia.Visuals/Media/Brush.cs
index d4894e0d14..a19d5af8b7 100644
--- a/src/Avalonia.Visuals/Media/Brush.cs
+++ b/src/Avalonia.Visuals/Media/Brush.cs
@@ -19,6 +19,11 @@ namespace Avalonia.Media
         /// <inheritdoc/>
         public event EventHandler Invalidated;
 
+        static Brush()
+        {
+            AffectsRender<Brush>(OpacityProperty);
+        }
+
         /// <summary>
         /// Gets or sets the opacity of the brush.
         /// </summary>