Merge pull request #5896 from AvaloniaUI/fixes/skia-drawingcontext-nre

Fix NRE in Skia DrawingContextImpl.

src/Skia/Avalonia.Skia/DrawingContextImpl.cs

@@ -166,7 +166,10 @@ namespace Avalonia.Skia
         {
             using (var paint = CreatePaint(_strokePaint, pen, new Size(Math.Abs(p2.X - p1.X), Math.Abs(p2.Y - p1.Y))))
             {
-                Canvas.DrawLine((float) p1.X, (float) p1.Y, (float) p2.X, (float) p2.Y, paint.Paint);
+                if (paint.Paint is object)
+                {
+                    Canvas.DrawLine((float)p1.X, (float)p1.Y, (float)p2.X, (float)p2.Y, paint.Paint);
+                }
             }
         }
 
@@ -361,7 +364,6 @@ namespace Avalonia.Skia
                     {
                         Canvas.DrawRect(rc, paint.Paint);
                     }
-                  
                 }
             }
 
@@ -397,15 +399,17 @@ namespace Avalonia.Skia
             {
                 using (var paint = CreatePaint(_strokePaint, pen, rect.Rect.Size))
                 {
-                    if (isRounded)
-                    {
-                        Canvas.DrawRoundRect(skRoundRect, paint.Paint);
-                    }
-                    else
+                    if (paint.Paint is object)
                     {
-                        Canvas.DrawRect(rc, paint.Paint);
+                        if (isRounded)
+                        {
+                            Canvas.DrawRoundRect(skRoundRect, paint.Paint);
+                        }
+                        else
+                        {
+                            Canvas.DrawRect(rc, paint.Paint);
+                        }
                     }
-                   
                 }
             }
         }

tests/Avalonia.Skia.UnitTests/DrawingContextImplTests.cs

@@ -0,0 +1,30 @@
+using Avalonia.Media;
+using Avalonia.Skia.Helpers;
+using SkiaSharp;
+using Xunit;
+
+namespace Avalonia.Skia.UnitTests
+{
+    public class DrawingContextImplTests
+    {
+        [Fact]
+        public void DrawLine_With_Zero_Thickness_Pen_Does_Not_Throw()
+        {
+            var target = CreateTarget();
+            target.DrawLine(new Pen(Brushes.Black, 0), new Point(0, 0), new Point(10, 10));
+        }
+
+        [Fact]
+        public void DrawRectangle_With_Zero_Thickness_Pen_Does_Not_Throw()
+        {
+            var target = CreateTarget();
+            target.DrawRectangle(Brushes.Black, new Pen(Brushes.Black, 0), new RoundedRect(new Rect(0, 0, 100, 100), new CornerRadius(4)));
+        }
+
+        private DrawingContextImpl CreateTarget()
+        {
+            var canvas = new SKCanvas(new SKBitmap(100, 100));
+            return (DrawingContextImpl)DrawingContextHelper.WrapSkiaCanvas(canvas, new Vector(96, 96));
+        }
+    }
+}