[Android] Fix LinearGradientBrush rendering as opaque black box

src/Controls/tests/TestCases.HostApp/Issues/Issue35280.cs

@@ -0,0 +1,79 @@
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Shapes;
+using Microsoft.Maui.Graphics;
+
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 35280, "LinearGradientBrush with transparent stops renders as opaque black box on Android", PlatformAffected.Android)]
+public class Issue35280 : ContentPage
+{
+	public Issue35280()
+	{
+		Label label = new Label
+		{
+			AutomationId = "DescriptionLabel",
+			Text = "The image below should have a gradient overlay that fades from black to transparent. If the image is completely covered by a black box, then the test has failed."
+		};
+
+		var border = new Border
+		{
+			Stroke = Colors.Transparent,
+			Margin = new Thickness(5, 0, 0, 0),
+			WidthRequest = 250,
+			StrokeShape = new RoundRectangle
+			{
+				CornerRadius = new CornerRadius(10)
+			},
+			Content = new Grid
+			{
+				Children =
+				{
+					new Image
+					{
+						Source = "dotnet_bot.png",
+						Aspect = Aspect.AspectFill
+					},
+					new VerticalStackLayout
+					{
+						VerticalOptions = LayoutOptions.End,
+						Padding = 10,
+						Background = new LinearGradientBrush
+						{
+							StartPoint = new Point(0, 1),
+							EndPoint = new Point(1, 0),
+							GradientStops = new GradientStopCollection
+							{
+								new GradientStop { Color = Colors.Black, Offset = 0.0f },
+								new GradientStop { Color = Color.FromArgb("#80000000"), Offset = 0.5f },
+								new GradientStop { Color = Colors.Transparent, Offset = 1.0f }
+							}
+						},
+						Children =
+						{
+							new Label
+							{
+								Text = "Title",
+								TextColor = Colors.White
+							},
+							new Label
+							{
+								Text = "Subtitle",
+								TextColor = Colors.White
+							}
+						}
+					}
+				}
+			}
+		};
+
+		Content = new VerticalStackLayout
+		{
+			Padding = 20,
+			Children =
+			{
+				label,
+				border
+			}
+		};
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue35280.cs

@@ -0,0 +1,25 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue35280 : _IssuesUITest
+{
+	public Issue35280(TestDevice device) : base(device) { }
+
+	public override string Issue => "LinearGradientBrush with transparent stops renders as opaque black box on Android";
+
+	[Test]
+	[Category(UITestCategories.Brush)]
+	public void LinearGradientBrushTransparentStopsShouldNotBeOpaque()
+	{
+		// Wait for the gradient container to be visible
+		App.WaitForElement("DescriptionLabel");
+
+		// The gradient has transparent/semi-transparent stops.
+		// With the bug (GetGradientData(1.0f)), all stops are forced fully opaque → solid black box.
+		// With the fix (GetGradientData(null)), per-stop alpha is preserved → red background shows through.
+		VerifyScreenshot(retryTimeout: TimeSpan.FromSeconds(2));
+	}
+}

src/Core/src/Graphics/MauiDrawable.Android.cs

@@ -112,7 +112,7 @@ public void SetBackground(LinearGradientPaint linearGradientPaint)
 
 			_background = linearGradientPaint;
 
-			var gradientData = linearGradientPaint.GetGradientData(1.0f);
+			var gradientData = linearGradientPaint.GetGradientData(null);
 
 			SetLinearGradientBackground(gradientData.X1, gradientData.Y1, gradientData.X2, gradientData.Y2, gradientData.Colors, gradientData.Offsets);
 		}
@@ -126,7 +126,7 @@ public void SetBackground(RadialGradientPaint radialGradientPaint)
 
 			_background = radialGradientPaint;
 
-			var gradientData = radialGradientPaint.GetGradientData(1.0f);
+			var gradientData = radialGradientPaint.GetGradientData(null);
 
 			SetRadialGradientBackground(gradientData.CenterX, gradientData.CenterY, gradientData.Radius, gradientData.Colors, gradientData.Offsets);
 		}
@@ -247,7 +247,7 @@ public void SetBorderBrush(LinearGradientPaint linearGradientPaint)
 
 			_stroke = linearGradientPaint;
 
-			var gradientData = linearGradientPaint.GetGradientData(1.0f);
+			var gradientData = linearGradientPaint.GetGradientData(null);
 
 			SetLinearGradientBorder(gradientData.X1, gradientData.Y1, gradientData.X2, gradientData.Y2, gradientData.Colors, gradientData.Offsets);
 		}
@@ -261,7 +261,7 @@ public void SetBorderBrush(RadialGradientPaint radialGradientPaint)
 
 			_stroke = radialGradientPaint;
 
-			var gradientData = radialGradientPaint.GetGradientData(1.0f);
+			var gradientData = radialGradientPaint.GetGradientData(null);
 
 			SetRadialGradientBorder(gradientData.CenterX, gradientData.CenterY, gradientData.Radius, gradientData.Colors, gradientData.Offsets);
 		}