feat: Avoid faux linear gradients on borders on iOS and macOS

src/Uno.UI.RuntimeTests/Tests/Microsoft_UI_Xaml_Controls/Given_NumberBox.cs

@@ -9,6 +9,15 @@
 using Uno.UI.RuntimeTests.Helpers;
 using static Private.Infrastructure.TestServices;
 
+#if WINAPPSDK
+using Uno.UI.Extensions;
+#elif __IOS__
+using UIKit;
+#elif __MACOS__
+using AppKit;
+#else
+#endif
+
 #if !HAS_UNO_WINUI
 using Microsoft/* UWP don't rename */.UI.Xaml.Controls;
 #endif
@@ -49,4 +58,4 @@ public async Task When_Fluent_And_Theme_Changed()
 		}
 	}
 }
-#endif
+#endif

src/Uno.UI/UI/Xaml/Controls/Border/BorderLayerRenderer.iOSmacOS.cs

@@ -234,7 +234,7 @@ void OnImageChanged(_Image _)
 
 			var borderCALayer = borderBrush switch
 			{
-				GradientBrush gradientBorder => gradientBorder.GetLayer(area.Size),
+				GradientBrush gradientBorder when gradientBorder.CanApplyToBorder(cornerRadius) => gradientBorder.GetLayer(area.Size),
 				RadialGradientBrush radialBorder => radialBorder.GetLayer(area.Size),
 				_ => null,
 			};
@@ -252,11 +252,11 @@ void OnImageChanged(_Image _)
 				var borderLayerIndex = parent.Sublayers.Length;
 				CreateGradientBrushLayers(area, area, parent, sublayers, ref borderLayerIndex, borderCALayer, fillMask);
 			}
-			else if (borderBrush is SolidColorBrush scbBorder || borderBrush == null)
+			else
 			{
 				Action onInvalidateRender = () =>
 				{
-					CGColor color = Brush.GetFallbackColor(borderBrush);
+					CGColor color = GetNonGradientBorderColor(borderBrush);
 					outerLayer.StrokeColor = color;
 					outerLayer.FillColor = color;
 
@@ -382,7 +382,7 @@ imageData.NativeImage is _Image uiImage &&
 
 				var borderCALayer = borderBrush switch
 				{
-					GradientBrush gradientBorder => gradientBorder.GetLayer(area.Size),
+					GradientBrush gradientBorder when gradientBorder.CanApplyToBorder(cornerRadius) => gradientBorder.GetLayer(area.Size),
 					RadialGradientBrush radialBorder => radialBorder.GetLayer(area.Size),
 					_ => null,
 				};
@@ -400,12 +400,13 @@ imageData.NativeImage is _Image uiImage &&
 					var borderLayerIndex = parent.Sublayers.Length;
 					CreateGradientBrushLayers(area, area, parent, sublayers, ref borderLayerIndex, borderCALayer, fillMask);
 				}
-				else if (borderBrush is SolidColorBrush scbBorder)
+				else
 				{
-					Action onInvalidateRender = () => layer.FillColor = Brush.GetFallbackColor(borderBrush);
+					Action onInvalidateRender = () => layer.FillColor = GetNonGradientBorderColor(borderBrush);
+
 					onInvalidateRender();
-					scbBorder.InvalidateRender += onInvalidateRender;
-					new DisposableAction(() => scbBorder.InvalidateRender -= onInvalidateRender).DisposeWith(disposables);
+					borderBrush.InvalidateRender += onInvalidateRender;
+					new DisposableAction(() => borderBrush.InvalidateRender -= onInvalidateRender).DisposeWith(disposables);
 				}
 			}
 
@@ -442,6 +443,18 @@ imageData.NativeImage is _Image uiImage &&
 		return disposables;
 	}
 
+	private static Color GetNonGradientBorderColor(Brush borderBrush)
+	{
+		if (borderBrush is LinearGradientBrush linearGradientBrush && linearGradientBrush.SupportsFauxGradientBorder())
+		{
+			return linearGradientBrush.MajorStopColor ?? linearGradientBrush.FallbackColorWithOpacity;
+		}
+		else
+		{
+			return Brush.GetFallbackColor(borderBrush);
+		}
+	}
+
 	/// <summary>
 	/// Get a path that describes the rounded border.
 	/// </summary>

src/Uno.UI/UI/Xaml/Media/LinearGradiientBrush.faux.cs

@@ -27,7 +27,7 @@ internal override bool CanApplyToBorder(CornerRadius cornerRadius)
 #if __WASM__
 		return cornerRadius == CornerRadius.None;
 #elif __IOS__ || __MACOS__
-		return RelativeTransform == null;
+		return cornerRadius == CornerRadius.None && RelativeTransform == null;
 #else
 		return true;
 #endif