Refactor creating a stroked path.

- Move the logic into `SKPathHelper.CreateStrokedPath`; called from `PathHelper` and `GetWidenedGeometry`
- Use a pen hash code to check if we're up-to-date in `PathHelper` and include the dash style in that

src/Skia/Avalonia.Skia/GeometryImpl.cs

@@ -3,6 +3,7 @@ using System.Diagnostics.CodeAnalysis;
 using Avalonia.Media;
 using Avalonia.Platform;
 using Avalonia.Skia.Helpers;
+using Avalonia.Utilities;
 using SkiaSharp;
 
 namespace Avalonia.Skia
@@ -78,10 +79,7 @@ namespace Avalonia.Skia
 
         public IGeometryImpl GetWidenedGeometry(IPen pen)
         {
-            using var cache = new PathCache();
-            cache.UpdateIfNeeded(StrokePath, pen, includeDashStyle: true);
-
-            if (cache.ExpandedPath is { } path)
+            if (StrokePath is not null && SKPathHelper.CreateStrokedPath(StrokePath, pen) is { } path)
             {
                 // The path returned to us by skia here does not have closed figures.
                 // Fix that by calling CreateClosedPath.
@@ -162,60 +160,34 @@ namespace Avalonia.Skia
 
         private struct PathCache : IDisposable
         {
-            private double _width, _miterLimit;
-            private PenLineCap _cap;
-            private PenLineJoin _join;
+            private int _penHash;
             private SKPath? _path, _cachedFor;
             private Rect? _renderBounds;
             private static readonly SKPath s_emptyPath = new();
             
-
             public Rect RenderBounds => _renderBounds ??= (_path ?? _cachedFor ?? s_emptyPath).Bounds.ToAvaloniaRect();
             public SKPath ExpandedPath => _path ?? s_emptyPath;
 
-            public void UpdateIfNeeded(SKPath? strokePath, IPen? pen, bool includeDashStyle = false)
+            public void UpdateIfNeeded(SKPath? strokePath, IPen? pen)
             {
-                var strokeWidth = pen?.Thickness ?? 0;
-                var miterLimit = pen?.MiterLimit ?? 0;
-                var cap = pen?.LineCap ?? default;
-                var join = pen?.LineJoin ?? default;
-                
-                if (_cachedFor == strokePath
-                    && _path != null
-                    && cap == _cap
-                    && join == _join
-                    && Math.Abs(_width - strokeWidth) < float.Epsilon
-                    && (join != PenLineJoin.Miter || Math.Abs(_miterLimit - miterLimit) > float.Epsilon))
+                if (PenHelper.GetHashCode(pen, includeBrush: false) is { } penHash &&
+                    penHash == _penHash &&
+                    strokePath == _cachedFor)
+                {
                     // We are up to date
                     return;
+                }
 
                 _renderBounds = null;
                 _cachedFor = strokePath;
-                _width = strokeWidth;
-                _cap = cap;
-                _join = join;
-                _miterLimit = miterLimit;
-                
-                if (strokePath == null || Math.Abs(strokeWidth) < float.Epsilon)
-                {
-                    _path = null;
-                    return;
-                }
-
-                var paint = SKPaintCache.Shared.Get();
-                paint.IsStroke = true;
-                paint.StrokeWidth = (float)_width;
-                paint.StrokeCap = cap.ToSKStrokeCap();
-                paint.StrokeJoin = join.ToSKStrokeJoin();
-                paint.StrokeMiter = (float)miterLimit;
-
-                if (includeDashStyle && DrawingContextHelper.TryCreateDashEffect(pen, out var dashEffect))
-                    paint.PathEffect = dashEffect;
+                _penHash = penHash;
+                _path?.Dispose();
 
-                _path = new SKPath();
-                paint.GetFillPath(strokePath, _path);
+                if (strokePath is not null && pen is not null)
+                    _path = SKPathHelper.CreateStrokedPath(strokePath, pen);
+                else
+                    _path = null;
 
-                SKPaintCache.Shared.ReturnReset(paint);
             }
 
             public void Dispose()
@@ -223,7 +195,6 @@ namespace Avalonia.Skia
                 _path?.Dispose();
                 _path = null;
             }
-
         }
     }
 }

src/Skia/Avalonia.Skia/Helpers/PenHelper.cs

@@ -0,0 +1,38 @@
+using System;
+using Avalonia.Media;
+
+namespace Avalonia.Skia.Helpers;
+
+internal static class PenHelper
+{
+    /// <summary>
+    /// Gets a hash code for a pen, optionally including the brush.
+    /// </summary>
+    /// <param name="pen">The pen.</param>
+    /// <param name="includeBrush">Whether to include the brush in the hash code.</param>
+    /// <returns>The hash code.</returns>
+    public static int GetHashCode(IPen? pen, bool includeBrush)
+    {
+        if (pen is null)
+            return 0;
+
+        var hash = new HashCode();
+        hash.Add(pen.LineCap);
+        hash.Add(pen.LineJoin);
+        hash.Add(pen.MiterLimit);
+        hash.Add(pen.Thickness);
+
+        if (pen.DashStyle is { } dashStyle)
+        {
+            hash.Add(dashStyle.Offset);
+
+            for (var i = 0; i < dashStyle.Dashes?.Count; i++)
+                hash.Add(dashStyle.Dashes[i]);
+        }
+
+        if (includeBrush)
+            hash.Add(pen.Brush);
+
+        return hash.ToHashCode();
+    }
+}

src/Skia/Avalonia.Skia/Helpers/SKPathHelper.cs

@@ -1,9 +1,17 @@
-using SkiaSharp;
+using System;
+using Avalonia.Media;
+using Avalonia.Utilities;
+using SkiaSharp;
 
 namespace Avalonia.Skia.Helpers;
 
 internal static class SKPathHelper
 {
+    /// <summary>
+    /// Creates a new path that is a closed version of the source path.
+    /// </summary>
+    /// <param name="path">The source path.</param>
+    /// <returns>A closed path.</returns>
     public static SKPath CreateClosedPath(SKPath path)
     {
         using var iter = path.CreateIterator(true);
@@ -29,4 +37,31 @@ internal static class SKPathHelper
 
         return rv;
     }
+
+    /// <summary>
+    /// Creates a path that is the result of a pen being applied to the stroke of the given path.
+    /// </summary>
+    /// <param name="path">The path to stroke.</param>
+    /// <param name="pen">The pen to use to stroke the path.</param>
+    /// <returns>The resulting path, or null if the pen has 0 thickness.</returns>
+    public static SKPath? CreateStrokedPath(SKPath path, IPen pen)
+    {
+        if (MathUtilities.IsZero(pen.Thickness))
+            return null;
+
+        var paint = SKPaintCache.Shared.Get();
+        paint.IsStroke = true;
+        paint.StrokeWidth = (float)pen.Thickness;
+        paint.StrokeCap = pen.LineCap.ToSKStrokeCap();
+        paint.StrokeJoin = pen.LineJoin.ToSKStrokeJoin();
+        paint.StrokeMiter = (float)pen.MiterLimit;
+
+        if (DrawingContextHelper.TryCreateDashEffect(pen, out var dashEffect))
+            paint.PathEffect = dashEffect;
+
+        var result = new SKPath();
+        paint.GetFillPath(path, result);
+        SKPaintCache.Shared.ReturnReset(paint);
+        return result;
+    }
 }