Fix GraphicsView scaling after canvas.ResetState on Android (#31183)

kubaflo · kubaflo · commit 1f5860066a97 · 2026-03-16T22:28:02.000+01:00
diff --git a/src/Controls/tests/TestCases.HostApp/Issues/Issue31182.cs b/src/Controls/tests/TestCases.HostApp/Issues/Issue31182.cs
@@ -0,0 +1,57 @@
+﻿namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 31182, "GraphicsView draws at half size after canvas.ResetState()", PlatformAffected.Android)]
+public class Issue31182 : TestContentPage
+{
+	protected override void Init()
+	{
+		var someView = new SomeView
+		{
+			WidthRequest = 200,
+			HeightRequest = 200
+		};
+
+		var label = new Label
+		{
+			Text = "Invalidated",
+			AutomationId = "label",
+			IsVisible = true
+		};
+
+		someView.Loaded += (s, e) =>
+		{
+			Dispatcher.DispatchDelayed(TimeSpan.FromMilliseconds(100), () =>
+			{
+				MainThread.BeginInvokeOnMainThread(() =>
+				{
+					someView.Invalidate();
+					label.IsVisible = true;
+				});
+			});
+		};
+
+		Content = new VerticalStackLayout
+		{
+			WidthRequest = 200,
+			HeightRequest = 200,
+			Background = Colors.Red,
+			Children =
+			{
+				someView,
+				label
+			}
+		};
+	}
+
+	class SomeView : GraphicsView, IDrawable
+	{
+		public SomeView() { Drawable = this; }
+
+		public void Draw(ICanvas canvas, RectF dirtyRect)
+		{
+			canvas.ResetState();
+			canvas.FillColor = Colors.Yellow;
+			canvas.FillRectangle(dirtyRect);
+		}
+	}
+}
diff --git a/src/Controls/tests/TestCases.Mac.Tests/snapshots/mac/GraphicsViewShouldDrawAtFullSize.png b/src/Controls/tests/TestCases.Mac.Tests/snapshots/mac/GraphicsViewShouldDrawAtFullSize.png
diff --git a/src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue31182.cs b/src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue31182.cs
@@ -0,0 +1,20 @@
+﻿using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue31182 : _IssuesUITest
+{
+	public Issue31182(TestDevice testDevice) : base(testDevice) { }
+
+	public override string Issue => "GraphicsView draws at half size after canvas.ResetState()";
+
+	[Test]
+	[Category(UITestCategories.GraphicsView)]
+	public void GraphicsViewShouldDrawAtFullSize()
+	{
+		App.WaitForElement("label");
+		VerifyScreenshot();
+	}
+}
diff --git a/src/Controls/tests/TestCases.iOS.Tests/snapshots/ios/GraphicsViewShouldDrawAtFullSize.png b/src/Controls/tests/TestCases.iOS.Tests/snapshots/ios/GraphicsViewShouldDrawAtFullSize.png
diff --git a/src/Graphics/src/Graphics/Platforms/Android/PlatformGraphicsView.cs b/src/Graphics/src/Graphics/Platforms/Android/PlatformGraphicsView.cs
@@ -19,15 +19,15 @@ public PlatformGraphicsView(Context context, IAttributeSet attrs, IDrawable draw
 		{
 			_scale = Resources.DisplayMetrics.Density;
 			_canvas = new PlatformCanvas(context);
-			_scalingCanvas = new ScalingCanvas(_canvas);
+			_scalingCanvas = new ScalingCanvas(_canvas, _scale);
 			Drawable = drawable;
 		}
 
 		public PlatformGraphicsView(Context context, IDrawable drawable = null) : base(context)
 		{
 			_scale = Resources.DisplayMetrics.Density;
 			_canvas = new PlatformCanvas(context);
-			_scalingCanvas = new ScalingCanvas(_canvas);
+			_scalingCanvas = new ScalingCanvas(_canvas, _scale);
 			Drawable = drawable;
 		}
 
@@ -67,7 +67,6 @@ public override void Draw(Canvas androidCanvas)
 			}
 
 			_scalingCanvas.ResetState();
-			_scalingCanvas.Scale(_scale, _scale);
 			//Since we are using a scaling canvas, we need to scale the rectangle
 			dirtyRect.Height /= _scale;
 			dirtyRect.Width /= _scale;
diff --git a/src/Graphics/src/Graphics/ScalingCanvas.cs b/src/Graphics/src/Graphics/ScalingCanvas.cs
@@ -17,6 +17,8 @@ public class ScalingCanvas : ICanvas, IBlurrableCanvas
 		private readonly Stack<float> _scaleYStack = new Stack<float>();
 		private float _scaleX = 1f;
 		private float _scaleY = 1f;
+		private float _initialScaleX = 1f;
+		private float _initialScaleY = 1f;
 
 		/// <summary>
 		/// Initializes a new instance of the <see cref="ScalingCanvas"/> class.
@@ -29,6 +31,12 @@ public ScalingCanvas(ICanvas wrapped)
 			_blurrableCanvas = _canvas as IBlurrableCanvas;
 		}
 
+		internal ScalingCanvas(ICanvas wrapped, float scale) : this(wrapped)
+		{
+			_initialScaleX = scale;
+			_initialScaleY = scale;
+		}
+
 		/// <inheritdoc/>
 		public float DisplayScale
 		{
@@ -271,8 +279,9 @@ public void ResetState()
 			_canvas.ResetState();
 			_scaleXStack.Clear();
 			_scaleYStack.Clear();
-			_scaleX = 1;
-			_scaleY = 1;
+			_scaleX = _initialScaleX;
+			_scaleY = _initialScaleY;
+			_canvas.Scale(_scaleX, _scaleY);
 		}
 
 		public bool RestoreState()
@@ -285,8 +294,8 @@ public bool RestoreState()
 			}
 			else
 			{
-				_scaleX = 1;
-				_scaleY = 1;
+				_scaleX = _initialScaleX;
+				_scaleY = _initialScaleY;
 			}
 
 			return restored;

Original file line number	Diff line number	Diff line change
`@@ -19,15 +19,15 @@ public PlatformGraphicsView(Context context, IAttributeSet attrs, IDrawable draw`
`19`	`19`	`{`
`20`	`20`	`_scale = Resources.DisplayMetrics.Density;`
`21`	`21`	`_canvas = new PlatformCanvas(context);`
`22`		`- _scalingCanvas = new ScalingCanvas(_canvas);`
	`22`	`+ _scalingCanvas = new ScalingCanvas(_canvas, _scale);`
`23`	`23`	`Drawable = drawable;`
`24`	`24`	`}`
`25`	`25`
`26`	`26`	`public PlatformGraphicsView(Context context, IDrawable drawable = null) : base(context)`
`27`	`27`	`{`
`28`	`28`	`_scale = Resources.DisplayMetrics.Density;`
`29`	`29`	`_canvas = new PlatformCanvas(context);`
`30`		`- _scalingCanvas = new ScalingCanvas(_canvas);`
	`30`	`+ _scalingCanvas = new ScalingCanvas(_canvas, _scale);`
`31`	`31`	`Drawable = drawable;`
`32`	`32`	`}`
`33`	`33`
`@@ -67,7 +67,6 @@ public override void Draw(Canvas androidCanvas)`
`67`	`67`	`}`
`68`	`68`
`69`	`69`	`_scalingCanvas.ResetState();`
`70`		`- _scalingCanvas.Scale(_scale, _scale);`
`71`	`70`	`//Since we are using a scaling canvas, we need to scale the rectangle`
`72`	`71`	`dirtyRect.Height /= _scale;`
`73`	`72`	`dirtyRect.Width /= _scale;`