Fix some issues with strokeless geometry segments (#16019)

* Added failing cross test.

For polyline segment with `IsStroked = false`.

* Fixed some issues with non-stroked segments

* Fix CombinedGeometryImpl with empty paths.

If an empty (but non-null) stroke was passed to `CombinedGeometryImpl` then its empty bounds would be used and the fill bounds ignored. Added a test and fixed that.

---------

Co-authored-by: Nikita Tsukanov <keks9n@gmail.com>

src/Avalonia.Base/Media/PolyLineSegment.cs

@@ -53,7 +53,7 @@ namespace Avalonia.Media
             {
                 for (int i = 0; i < points.Count; i++)
                 {
-                    ctx.LineTo(points[i]);
+                    ctx.LineTo(points[i], IsStroked);
                 }
             }
         }

src/Skia/Avalonia.Skia/CombinedGeometryImpl.cs

@@ -13,7 +13,13 @@ namespace Avalonia.Skia
         {
             StrokePath = stroke;
             FillPath = fill;
-            Bounds = (stroke ?? fill)?.TightBounds.ToAvaloniaRect() ?? default;
+
+            var bounds = stroke?.TightBounds ?? default;
+
+            if (fill != null)
+                bounds.Union(fill.TightBounds);
+
+            Bounds = bounds.ToAvaloniaRect();
         }
 
         public static CombinedGeometryImpl ForceCreate(GeometryCombineMode combineMode, IGeometryImpl g1, IGeometryImpl g2)

src/Skia/Avalonia.Skia/GeometryImpl.cs

@@ -80,7 +80,10 @@ namespace Avalonia.Skia
             lock (_lock)
             {
                 _pathCache.UpdateIfNeeded(StrokePath, pen);
-                return _pathCache.RenderBounds;
+                var bounds = _pathCache.RenderBounds;
+                if (StrokePath != FillPath && FillPath != null)
+                    bounds = bounds.Union(FillPath.Bounds.ToAvaloniaRect());
+                return bounds;
             }
         }
 

src/Skia/Avalonia.Skia/StreamGeometryImpl.cs

@@ -88,6 +88,22 @@ namespace Avalonia.Skia
             private bool _isFigureBroken;
             private bool Duplicate => _isFilled && !ReferenceEquals(_geometryImpl._fillPath, Stroke);
 
+            private void EnsureSeparateFillPath()
+            {
+                if (Stroke == Fill)
+                    _geometryImpl._fillPath = Stroke.Clone();
+            }
+            
+            private void BreakFigure()
+            {
+                if (!_isFigureBroken)
+                {
+                    _isFigureBroken = true;
+                    EnsureSeparateFillPath();
+                }
+                    
+            }
+
             /// <summary>
             /// Initializes a new instance of the <see cref="StreamContext"/> class.
             /// <param name="geometryImpl">Geometry to operate on.</param>
@@ -134,11 +150,8 @@ namespace Avalonia.Skia
             /// <inheritdoc />
             public void BeginFigure(Point startPoint, bool isFilled)
             {
-                if (!isFilled)
-                {
-                    if (Stroke == Fill)
-                        _geometryImpl._fillPath = Stroke.Clone();
-                }
+                if (!isFilled) 
+                    EnsureSeparateFillPath();
 
                 _isFilled = isFilled;
                 _startPoint = startPoint;
@@ -179,7 +192,7 @@ namespace Avalonia.Skia
                 {
                     if (_isFigureBroken)
                     {
-                        LineTo(_startPoint);
+                        Stroke.LineTo(_startPoint.ToSKPoint());
                         _isFigureBroken = false;
                     }
                     else
@@ -204,11 +217,7 @@ namespace Avalonia.Skia
                 }
                 else
                 {
-                    if (Stroke == Fill)
-                        _geometryImpl._fillPath = Stroke.Clone();
-
-                    _isFigureBroken = true;
-
+                    BreakFigure();
                     Stroke.MoveTo((float)point.X, (float)point.Y);
                 }
                 if (Duplicate)
@@ -236,11 +245,7 @@ namespace Avalonia.Skia
                 }
                 else
                 {
-                    if (Stroke == Fill)
-                        _geometryImpl._fillPath = Stroke.Clone();
-
-                    _isFigureBroken = true;
-
+                    BreakFigure();
                     Stroke.MoveTo((float)point.X, (float)point.Y);
                 }
                 if (Duplicate)
@@ -263,11 +268,7 @@ namespace Avalonia.Skia
                 }
                 else
                 {
-                    if (Stroke == Fill)
-                        _geometryImpl._fillPath = Stroke.Clone();
-
-                    _isFigureBroken = true;
-
+                    BreakFigure();
                     Stroke.MoveTo((float)point3.X, (float)point3.Y);
                 }
                 if (Duplicate)
@@ -283,11 +284,7 @@ namespace Avalonia.Skia
                 }
                 else
                 {
-                    if (Stroke == Fill)
-                        _geometryImpl._fillPath = Stroke.Clone();
-
-                    _isFigureBroken = true;
-
+                    BreakFigure();
                     Stroke.MoveTo((float)point2.X, (float)point2.Y);
                 }
                 if (Duplicate)

tests/Avalonia.RenderTests.WpfCompare/CrossUI.Wpf.cs

@@ -190,6 +190,7 @@ namespace Avalonia.RenderTests.WpfCompare
                                 CrossPathSegment.Arc arc => new ArcSegment(arc.Point.ToWpf(), arc.Size.ToWpf(), arc.RotationAngle, arc.IsLargeArc, (SweepDirection)arc.SweepDirection, s.IsStroked),
                                 CrossPathSegment.CubicBezier cubicBezier => new BezierSegment(cubicBezier.Point1.ToWpf(), cubicBezier.Point2.ToWpf(), cubicBezier.Point3.ToWpf(), cubicBezier.IsStroked),
                                 CrossPathSegment.QuadraticBezier quadraticBezier => new QuadraticBezierSegment(quadraticBezier.Point1.ToWpf(), quadraticBezier.Point2.ToWpf(), quadraticBezier.IsStroked),
+                                CrossPathSegment.PolyLine polyLine => new PolyLineSegment(polyLine.Points.Select(p => p.ToWpf()).ToList(), polyLine.IsStroked),
                                 _ => throw new NotImplementedException(),
                             }), f.Closed)))
                 };

tests/Avalonia.RenderTests/CrossTests/CrossGeometryTests.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Drawing.Drawing2D;
 using System.Linq;
 using Avalonia.Media;
 using CrossUI;
@@ -109,7 +110,37 @@ public class CrossGeometryTests : CrossTestBase
             Background = brush
         });
     }
-    
+
+
+    [CrossFact]
+    public void Should_Render_PolyLineSegment_With_Strokeless_Lines()
+    {
+        var brush = new CrossSolidColorBrush(Colors.Blue);
+        var pen = new CrossPen()
+        {
+            Brush = new CrossSolidColorBrush(Colors.Red),
+            Thickness = 8
+        };
+        var figure = new CrossPathFigure()
+        {
+            Closed = true,
+            Segments =
+            {
+                new CrossPathSegment.PolyLine([new(0, 0), new(100, 0), new(100, 100), new(0, 100), new(0, 0)], false)
+            }
+        };
+        var geometry = new CrossPathGeometry { Figures = { figure } };
+
+        var control = new CrossFuncControl(ctx => ctx.DrawGeometry(brush, pen, geometry))
+        { 
+            Width = 100, 
+            Height = 100,
+        };
+
+        RenderAndCompare(control,
+            $"{nameof(Should_Render_PolyLineSegment_With_Strokeless_Lines)}");
+    }
+
     // Skip the test for now
 #if !AVALONIA_SKIA
     [CrossTheory,

tests/Avalonia.RenderTests/CrossUI/CrossUI.Avalonia.cs

@@ -201,6 +201,11 @@ namespace Avalonia.Direct2D1.RenderTests.CrossUI
                                         Point2 = q.Point2,
                                         IsStroked = q.IsStroked
                                     },
+                                    CrossPathSegment.PolyLine p => new PolyLineSegment()
+                                    {
+                                        Points = p.Points.ToList(),
+                                        IsStroked = p.IsStroked
+                                    },
                                     _ => throw new InvalidOperationException()
                                 }))
                         }))

tests/Avalonia.RenderTests/CrossUI/CrossUI.cs

@@ -158,6 +158,7 @@ public abstract record class CrossPathSegment(bool IsStroked)
     public record Arc(Point Point, Size Size, double RotationAngle, bool IsLargeArc, SweepDirection SweepDirection, bool IsStroked) : CrossPathSegment(IsStroked);
     public record CubicBezier(Point Point1, Point Point2, Point Point3, bool IsStroked) : CrossPathSegment(IsStroked);
     public record QuadraticBezier(Point Point1, Point Point2, bool IsStroked) : CrossPathSegment(IsStroked);
+    public record PolyLine(IEnumerable<Point> Points, bool IsStroked) : CrossPathSegment(IsStroked);
 }
 
 public class CrossDrawingBrush : CrossTileBrush

tests/Avalonia.Skia.UnitTests/CombinedGeometryImplTests.cs

@@ -0,0 +1,23 @@
+using SkiaSharp;
+using Xunit;
+
+namespace Avalonia.Skia.UnitTests;
+
+public class CombinedGeometryImplTests
+{
+    [Fact]
+    public void Combining_Fill_With_Empty_Stroke_Returns_Fill_Bounds()
+    {
+        var fill = new SKPath();
+        fill.LineTo(100, 0);
+        fill.LineTo(100, 100);
+        fill.LineTo(0, 100);
+        fill.Close();
+
+        var stroke = new SKPath();
+
+        var result = new CombinedGeometryImpl(stroke, fill);
+
+        Assert.Equal(new Rect(0, 0, 100, 100), result.Bounds);
+    }
+}