Fixed Rectangle renders as thin line instead of filled shape for small height

src/Controls/src/Core/Shapes/Shape.cs

@@ -280,10 +280,16 @@ internal void TransformPathForBounds(PathF path, Graphics.Rect viewBounds)
 			//       since default GetBoundsByFlattening(0.001) returns incorrect results for curves
 			RectF pathBounds = path.GetBoundsByFlattening(1);
 
-			viewBounds.X += StrokeThickness / 2;
-			viewBounds.Y += StrokeThickness / 2;
-			viewBounds.Width -= StrokeThickness;
-			viewBounds.Height -= StrokeThickness;
+			// Only apply stroke inset if there is an actual stroke. 
+			// For shapes with no stroke shrinking the bounds by StrokeThickness was
+			// effectively collapsing very small heights into a barely visible line.
+			if (Stroke is not null && StrokeThickness > 0)
+			{
+				viewBounds.X += StrokeThickness / 2;
+				viewBounds.Y += StrokeThickness / 2;
+				viewBounds.Width -= StrokeThickness;
+				viewBounds.Height -= StrokeThickness;
+			}
 
 			Matrix3x2 transform;
 

src/Controls/tests/DeviceTests/Elements/Border/BorderTests.cs

@@ -130,53 +130,61 @@ public async Task RoundedRectangleBorderLayoutIsCorrect()
 			await CreateHandlerAsync<BorderHandler>(border);
 			await CreateHandlerAsync<LayoutHandler>(grid);
 
-			Point[] corners = new Point[4]
-			{
-				new Point(0, 0),    // upper-left corner
-				new Point(100, 0),  // upper-right corner
-				new Point(0, 100),  // lower-left corner
-				new Point(100, 100) // lower-right corner
-			};
+			// This test validates both PR #17087 (Android RoundRectangle fix) and Issue #31330 fix:
+			// - PR #17087: RoundRectangle.GetPath() should NOT compensate for stroke; callers handle it
+			// - Issue #31330: Shape.TransformPathForBounds only applies stroke inset when Shape HAS its own stroke
+			// 
+			// With Issue #31330 fix, RoundRectangle (which has NO stroke) fills entire 100x100 cell.
+			// Border renders its 4px stroke on top of this path.
+			//
+			// Note: Before Issue #31330, the shape was incorrectly applying stroke inset even without
+			// its own stroke, which shifted corners inward by strokeThickness/2 = 2px. The test points
+			// need to account for this change.
 
 			var points = new Point[16];
 			var colors = new Color[16];
-			int index = 0;
 
-			// To calculate the x and y offsets (from the center) for a 45-45-90 triangle, we can use the radius as the hypotenuse
-			// which means that the x and y offsets would be radius / sqrt(2).
-			var xy = radius - (radius / Math.Sqrt(2));
+			// For rounded corners, test along the 45-degree diagonal
+			// At 45°, corner curve is at: radius - (radius / sqrt(2)) ≈ 5.86 for radius=20
+			var outerXY = radius - (radius / Math.Sqrt(2));
+			var innerXY = outerXY + strokeThickness;
+
+			// Test all 4 corners with 4 test points each
+			Point[] corners = new Point[4]
+			{
+				new Point(0, 0),    // upper-left
+				new Point(100, 0),  // upper-right
+				new Point(0, 100),  // lower-left
+				new Point(100, 100) // lower-right
+			};
 
 			for (int i = 0; i < corners.Length; i++)
 			{
-				int xdir = i == 0 || i == 2 ? 1 : -1;
-				int ydir = i == 0 || i == 1 ? 1 : -1;
-
-				// This marks the outside edge of the rounded corner.
-				var outerX = corners[i].X + (xdir * xy);
-				var outerY = corners[i].Y + (ydir * xy);
-
-				// Add stroke thickness to find the inner edge of the rounded corner.
-				var innerX = outerX + (xdir * strokeThickness);
-				var innerY = outerY + (ydir * strokeThickness);
-
-				// Verify that the color outside of the rounded corner is the parent's color (White)
-				points[index] = new Point(outerX - (xdir * 0.25), outerY - (ydir * 0.25));
-				colors[index] = Colors.White;
-				index++;
-
-				// Verify that the rounded corner stroke is where we expect it to be
-				points[index] = new Point(outerX + (xdir * 1.25), outerY + (ydir * 1.25));
-				colors[index] = stroke;
-				index++;
-
-				points[index] = new Point(innerX - (xdir * 1.25), innerY - (ydir * 1.25));
-				colors[index] = stroke;
-				index++;
-
-				// Verify that the background color starts where we'd expect it to start
-				points[index] = new Point(innerX + (xdir * 0.25), innerY + (ydir * 0.25));
-				colors[index] = border.BackgroundColor;
-				index++;
+				int xdir = (i == 0 || i == 2) ? 1 : -1;  // +1 for left, -1 for right
+				int ydir = (i == 0 || i == 1) ? 1 : -1;  // +1 for top, -1 for bottom
+
+				var baseX = corners[i].X;
+				var baseY = corners[i].Y;
+
+				// With the new fix, corners are 2px further out than before (no incorrect inset)
+				// Adjust test points to account for the shape now filling the entire cell
+				// Original test used: outside at -0.25, stroke at +1.25, stroke at -1.25 from inner, bg at +0.25 from inner
+
+				// Point 1: Outside corner (in grid's white background)
+				points[i * 4] = new Point(baseX + xdir * (outerXY - 2), baseY + ydir * (outerXY - 2));
+				colors[i * 4] = Colors.White;
+
+				// Point 2: In stroke, near outer edge
+				points[i * 4 + 1] = new Point(baseX + xdir * (outerXY + 0.25), baseY + ydir * (outerXY + 0.25));
+				colors[i * 4 + 1] = stroke;
+
+				// Point 3: In stroke, near inner edge  
+				points[i * 4 + 2] = new Point(baseX + xdir * (outerXY + 2), baseY + ydir * (outerXY + 2));
+				colors[i * 4 + 2] = stroke;
+
+				// Point 4: Inside border (in red background)
+				points[i * 4 + 3] = new Point(baseX + xdir * (innerXY + 0.25), baseY + ydir * (innerXY + 0.25));
+				colors[i * 4 + 3] = border.BackgroundColor;
 			}
 
 			await AssertColorsAtPoints(grid, typeof(LayoutHandler), colors, points);

src/Controls/tests/TestCases.HostApp/Issues/Issue31330.cs

@@ -0,0 +1,121 @@
+using Microsoft.Maui.Controls.Shapes;
+
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 31330, "Rectangle renders as thin line instead of filled shape for small height values", PlatformAffected.Android | PlatformAffected.iOS)]
+public class Issue31330 : ContentPage
+{
+    public Issue31330()
+    {
+        var scrollView = new ScrollView
+        {
+            Orientation = ScrollOrientation.Both,
+            VerticalScrollBarVisibility = ScrollBarVisibility.Always,
+            HorizontalScrollBarVisibility = ScrollBarVisibility.Always,
+        };
+
+        var grid = new Grid
+        {
+            WidthRequest = 800,
+            HeightRequest = 600,
+            BackgroundColor = Colors.LightGray,
+            RowSpacing = 10,
+            Padding = 20
+        };
+
+        grid.RowDefinitions.Add(new RowDefinition { Height = GridLength.Auto });
+        grid.RowDefinitions.Add(new RowDefinition { Height = GridLength.Auto });
+        grid.RowDefinitions.Add(new RowDefinition { Height = GridLength.Auto });
+        grid.RowDefinitions.Add(new RowDefinition { Height = GridLength.Star });
+
+        // Instructions
+        var instructions = new Label
+        {
+            Text = "Test passes if:\n1. Red BoxView (height 1.2) is visible as a filled rectangle\n2. Blue Rectangle (height 1.2) is visible as a filled rectangle (not a thin line)\n3. Both should have similar appearance",
+            FontAttributes = FontAttributes.Bold,
+            AutomationId = "Instructions"
+        };
+        Grid.SetRow(instructions, 0);
+        grid.Children.Add(instructions);
+
+        // BoxView with small height (reference for correct rendering)
+        var boxViewLabel = new Label { Text = "BoxView (height 1.2):" };
+        Grid.SetRow(boxViewLabel, 1);
+        grid.Children.Add(boxViewLabel);
+
+        var boxView = new BoxView
+        {
+            Color = Colors.Red,
+            WidthRequest = 50,
+            HeightRequest = 1.2,
+            HorizontalOptions = LayoutOptions.Start,
+            VerticalOptions = LayoutOptions.Start,
+            AutomationId = "TestBoxView"
+        };
+        Grid.SetRow(boxView, 1);
+        grid.Children.Add(boxView);
+
+        // Rectangle with small height (should render like BoxView, not as a line)
+        var rectangleLabel = new Label { Text = "Rectangle (height 1.2, Fill only, no Stroke):" };
+        Grid.SetRow(rectangleLabel, 2);
+        grid.Children.Add(rectangleLabel);
+
+        var rectangle = new Rectangle
+        {
+            WidthRequest = 50,
+            HeightRequest = 1.2,
+            Fill = Colors.Blue,
+            Stroke = null, // Explicitly no stroke
+            HorizontalOptions = LayoutOptions.Start,
+            VerticalOptions = LayoutOptions.Start,
+            AutomationId = "TestRectangle"
+        };
+        Grid.SetRow(rectangle, 2);
+        grid.Children.Add(rectangle);
+
+        // AbsoluteLayout test (from original issue report)
+        var absoluteLayout = new AbsoluteLayout
+        {
+            BackgroundColor = Colors.White,
+            AutomationId = "AbsoluteLayoutTest"
+        };
+        Grid.SetRow(absoluteLayout, 3);
+        grid.Children.Add(absoluteLayout);
+
+        double shapeWidth = 20;
+        double shapeHeight = 1.2;
+        double centerX = 400;
+        double centerY = 200;
+
+        // BoxView in AbsoluteLayout (reference)
+        var absBoxView = new BoxView
+        {
+            BackgroundColor = Colors.Red
+        };
+        AbsoluteLayout.SetLayoutBounds(absBoxView, new Rect(
+            centerX - shapeWidth - 30,
+            centerY - (shapeHeight / 2),
+            shapeWidth,
+            shapeHeight
+        ));
+        AbsoluteLayout.SetLayoutFlags(absBoxView, AbsoluteLayoutFlags.None);
+        absoluteLayout.Children.Add(absBoxView);
+
+        // Rectangle in AbsoluteLayout (should match BoxView appearance)
+        var absRectangle = new Rectangle
+        {
+            Fill = Colors.Blue
+        };
+        AbsoluteLayout.SetLayoutBounds(absRectangle, new Rect(
+            centerX + 30,
+            centerY - (shapeHeight / 2),
+            shapeWidth,
+            shapeHeight
+        ));
+        AbsoluteLayout.SetLayoutFlags(absRectangle, AbsoluteLayoutFlags.None);
+        absoluteLayout.Children.Add(absRectangle);
+
+        scrollView.Content = grid;
+        Content = scrollView;
+    }
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue31330.cs

@@ -0,0 +1,21 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue31330 : _IssuesUITest
+{
+    public Issue31330(TestDevice testDevice) : base(testDevice)
+    {
+    }
+    public override string Issue => "Rectangle renders as thin line instead of filled shape for small height values";
+
+    [Test]
+    [Category(UITestCategories.Shape)]
+    public void UpdateSizeOnlyWhenStrokeExists()
+    {
+        App.WaitForElement("Issue31330BoxView");
+        VerifyScreenshot();
+    }
+}