Use PolygonClipper

Author: JimBobSquarePants

ImageSharp.Drawing.sln

@@ -337,6 +337,8 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "workflows", "workflows", "{
 		.github\workflows\build-and-test.yml = .github\workflows\build-and-test.yml
 	EndProjectSection
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "PolygonClipper", "..\..\SixLabors\PolygonClipper\src\PolygonClipper\PolygonClipper.csproj", "{5ED54794-99BF-5E50-A861-0BAAAC794E44}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -359,6 +361,10 @@ Global
 		{5493F024-0A3F-420C-AC2D-05B77A36025B}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{5493F024-0A3F-420C-AC2D-05B77A36025B}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{5493F024-0A3F-420C-AC2D-05B77A36025B}.Release|Any CPU.Build.0 = Release|Any CPU
+		{5ED54794-99BF-5E50-A861-0BAAAC794E44}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{5ED54794-99BF-5E50-A861-0BAAAC794E44}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{5ED54794-99BF-5E50-A861-0BAAAC794E44}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{5ED54794-99BF-5E50-A861-0BAAAC794E44}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -386,12 +392,14 @@ Global
 		{68A8CC40-6AED-4E96-B524-31B1158FDEEA} = {815C0625-CD3D-440F-9F80-2D83856AB7AE}
 		{5493F024-0A3F-420C-AC2D-05B77A36025B} = {528610AC-7C0C-46E8-9A2D-D46FD92FEE29}
 		{23859314-5693-4E6C-BE5C-80A433439D2A} = {1799C43E-5C54-4A8F-8D64-B1475241DB0D}
+		{5ED54794-99BF-5E50-A861-0BAAAC794E44} = {815C0625-CD3D-440F-9F80-2D83856AB7AE}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {5F8B9D1F-CD8B-4CC5-8216-D531E25BD795}
 	EndGlobalSection
 	GlobalSection(SharedMSBuildProjectFiles) = preSolution
 		shared-infrastructure\src\SharedInfrastructure\SharedInfrastructure.projitems*{2e33181e-6e28-4662-a801-e2e7dc206029}*SharedItemsImports = 5
+		..\..\SixLabors\PolygonClipper\shared-infrastructure\src\SharedInfrastructure\SharedInfrastructure.projitems*{5ed54794-99bf-5e50-a861-0baaac794e44}*SharedItemsImports = 5
 		shared-infrastructure\src\SharedInfrastructure\SharedInfrastructure.projitems*{68a8cc40-6aed-4e96-b524-31b1158fdeea}*SharedItemsImports = 13
 	EndGlobalSection
 	GlobalSection(Performance) = preSolution

src/ImageSharp.Drawing/ImageSharp.Drawing.csproj

@@ -47,5 +47,8 @@
     <PackageReference Include="SixLabors.Fonts" Version="3.0.0-alpha.0.3" />
     <PackageReference Include="SixLabors.ImageSharp" Version="4.0.0-alpha.0.49" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\..\SixLabors\PolygonClipper\src\PolygonClipper\PolygonClipper.csproj" />
+  </ItemGroup>
   <Import Project="..\..\shared-infrastructure\src\SharedInfrastructure\SharedInfrastructure.projitems" Label="Shared" />
 </Project>

src/ImageSharp.Drawing/Processing/Processors/Drawing/DrawPathProcessor.cs

@@ -48,7 +48,20 @@ public IImageProcessor<TPixel> CreatePixelSpecificProcessor<TPixel>(Configuratio
         // The global transform is applied in the FillPathProcessor.
         IPath outline = this.Pen.GeneratePath(this.Path.Transform(Matrix3x2.CreateTranslation(0.5F, 0.5F)));
 
-        return new FillPathProcessor(this.Options, this.Pen.StrokeFill, outline)
+        DrawingOptions effectiveOptions = this.Options;
+
+        // Non-normalized stroked output can contain overlaps/self-intersections.
+        // Rasterizing these contours with non-zero winding matches the intended stroke semantics.
+        if (!this.Pen.StrokeOptions.NormalizeOutput &&
+            this.Options.ShapeOptions.IntersectionRule != IntersectionRule.NonZero)
+        {
+            ShapeOptions shapeOptions = this.Options.ShapeOptions.DeepClone();
+            shapeOptions.IntersectionRule = IntersectionRule.NonZero;
+
+            effectiveOptions = new DrawingOptions(this.Options.GraphicsOptions, shapeOptions, this.Options.Transform);
+        }
+
+        return new FillPathProcessor(effectiveOptions, this.Pen.StrokeFill, outline)
             .CreatePixelSpecificProcessor(configuration, source, sourceRectangle);
     }
 }

src/ImageSharp.Drawing/Processing/StrokeOptions.cs

@@ -8,20 +8,32 @@ namespace SixLabors.ImageSharp.Drawing.Processing;
 /// </summary>
 public sealed class StrokeOptions : IEquatable<StrokeOptions?>
 {
+    /// <summary>
+    /// Gets or sets a value indicating whether stroked contours should be normalized by
+    /// resolving self-intersections and overlaps before returning.
+    /// </summary>
+    /// <remarks>
+    /// Defaults to <see langword="false"/> for maximum throughput.
+    /// When disabled, callers should rasterize with a non-zero winding fill rule.
+    /// </remarks>
+    public bool NormalizeOutput { get; set; }
+
     /// <summary>
     /// Gets or sets the miter limit used to clamp outer miter joins.
     /// </summary>
-    public double MiterLimit { get; set; } = 4;
+    public double MiterLimit { get; set; } = 4D;
 
     /// <summary>
     /// Gets or sets the inner miter limit used to clamp joins on acute interior angles.
     /// </summary>
-    public double InnerMiterLimit { get; set; } = 1.01;
+    public double InnerMiterLimit { get; set; } = 1.01D;
 
     /// <summary>
-    /// Gets or sets the arc approximation scale used for round joins and caps.
+    /// Gets or sets the tessellation detail scale for round joins and round caps.
+    /// Higher values produce more vertices (smoother curves, more work).
+    /// Lower values produce fewer vertices.
     /// </summary>
-    public double ApproximationScale { get; set; } = 1.0;
+    public double ArcDetailScale { get; set; } = 1D;
 
     /// <summary>
     /// Gets or sets the outer line join style used for stroking corners.
@@ -44,19 +56,21 @@ public sealed class StrokeOptions : IEquatable<StrokeOptions?>
     /// <inheritdoc/>
     public bool Equals(StrokeOptions? other)
         => other is not null &&
-        this.MiterLimit == other.MiterLimit &&
-        this.InnerMiterLimit == other.InnerMiterLimit &&
-        this.ApproximationScale == other.ApproximationScale &&
-        this.LineJoin == other.LineJoin &&
-        this.LineCap == other.LineCap &&
-        this.InnerJoin == other.InnerJoin;
+           this.NormalizeOutput == other.NormalizeOutput &&
+           this.MiterLimit == other.MiterLimit &&
+           this.InnerMiterLimit == other.InnerMiterLimit &&
+           this.ArcDetailScale == other.ArcDetailScale &&
+           this.LineJoin == other.LineJoin &&
+           this.LineCap == other.LineCap &&
+           this.InnerJoin == other.InnerJoin;
 
     /// <inheritdoc/>
     public override int GetHashCode()
         => HashCode.Combine(
+            this.NormalizeOutput,
             this.MiterLimit,
             this.InnerMiterLimit,
-            this.ApproximationScale,
+            this.ArcDetailScale,
             this.LineJoin,
             this.LineCap,
             this.InnerJoin);

src/ImageSharp.Drawing/Shapes/ClipPathExtensions.cs

@@ -11,14 +11,16 @@ namespace SixLabors.ImageSharp.Drawing;
 /// </summary>
 public static class ClipPathExtensions
 {
+    private static readonly ShapeOptions DefaultOptions = new();
+
     /// <summary>
     /// Clips the specified subject path with the provided clipping paths.
     /// </summary>
     /// <param name="subjectPath">The subject path.</param>
     /// <param name="clipPaths">The clipping paths.</param>
     /// <returns>The clipped <see cref="IPath"/>.</returns>
     public static IPath Clip(this IPath subjectPath, params IPath[] clipPaths)
-        => subjectPath.Clip((IEnumerable<IPath>)clipPaths);
+        => subjectPath.Clip(DefaultOptions, clipPaths);
 
     /// <summary>
     /// Clips the specified subject path with the provided clipping paths.
@@ -31,7 +33,7 @@ public static IPath Clip(
         this IPath subjectPath,
         ShapeOptions options,
         params IPath[] clipPaths)
-        => subjectPath.Clip(options, (IEnumerable<IPath>)clipPaths);
+        => ClippedShapeGenerator.GenerateClippedShapes(options.BooleanOperation, subjectPath, clipPaths);
 
     /// <summary>
     /// Clips the specified subject path with the provided clipping paths.
@@ -40,7 +42,7 @@ public static IPath Clip(
     /// <param name="clipPaths">The clipping paths.</param>
     /// <returns>The clipped <see cref="IPath"/>.</returns>
     public static IPath Clip(this IPath subjectPath, IEnumerable<IPath> clipPaths)
-        => subjectPath.Clip(new ShapeOptions(), clipPaths);
+        => subjectPath.Clip(DefaultOptions, clipPaths);
 
     /// <summary>
     /// Clips the specified subject path with the provided clipping paths.
@@ -53,14 +55,5 @@ public static IPath Clip(
         this IPath subjectPath,
         ShapeOptions options,
         IEnumerable<IPath> clipPaths)
-    {
-        ClippedShapeGenerator clipper = new(options.IntersectionRule);
-
-        clipper.AddPath(subjectPath, ClippingType.Subject);
-        clipper.AddPaths(clipPaths, ClippingType.Clip);
-
-        IPath[] result = clipper.GenerateClippedShapes(options.BooleanOperation);
-
-        return new ComplexPolygon(result);
-    }
+        => ClippedShapeGenerator.GenerateClippedShapes(options.BooleanOperation, subjectPath, clipPaths);
 }

src/ImageSharp.Drawing/Shapes/ComplexPolygon.cs

@@ -1,7 +1,6 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
-using System.Buffers;
 using System.Diagnostics.CodeAnalysis;
 using System.Numerics;
 
@@ -34,7 +33,7 @@ public ComplexPolygon(PointF[] contour, PointF[] hole)
     /// </summary>
     /// <param name="paths">The paths.</param>
     public ComplexPolygon(IEnumerable<IPath> paths)
-        : this(paths.ToArray())
+        : this([.. paths])
     {
     }
 

src/ImageSharp.Drawing/Shapes/OutlinePathExtensions.cs

@@ -12,14 +12,16 @@ namespace SixLabors.ImageSharp.Drawing;
 /// </summary>
 public static class OutlinePathExtensions
 {
+    private static readonly StrokeOptions DefaultOptions = new();
+
     /// <summary>
     /// Generates an outline of the path.
     /// </summary>
     /// <param name="path">The path to outline</param>
     /// <param name="width">The outline width.</param>
     /// <returns>A new <see cref="IPath"/> representing the outline.</returns>
     public static IPath GenerateOutline(this IPath path, float width)
-        => GenerateOutline(path, width, new StrokeOptions());
+        => GenerateOutline(path, width, DefaultOptions);
 
     /// <summary>
     /// Generates an outline of the path.
@@ -35,8 +37,7 @@ public static IPath GenerateOutline(this IPath path, float width, StrokeOptions
             return Path.Empty;
         }
 
-        StrokedShapeGenerator generator = new(strokeOptions);
-        return new ComplexPolygon(generator.GenerateStrokedShapes(path, width));
+        return StrokedShapeGenerator.GenerateStrokedShapes(path, width, strokeOptions);
     }
 
     /// <summary>
@@ -69,7 +70,7 @@ public static IPath GenerateOutline(this IPath path, float width, ReadOnlySpan<f
     /// <param name="startOff">Whether the first item in the pattern is on or off.</param>
     /// <returns>A new <see cref="IPath"/> representing the outline.</returns>
     public static IPath GenerateOutline(this IPath path, float width, ReadOnlySpan<float> pattern, bool startOff)
-        => GenerateOutline(path, width, pattern, startOff, new StrokeOptions());
+        => GenerateOutline(path, width, pattern, startOff, DefaultOptions);
 
     /// <summary>
     /// Generates an outline of the path with alternating on and off segments based on the pattern.
@@ -235,7 +236,6 @@ public static IPath GenerateOutline(
         }
 
         // Each outline span is stroked as an open polyline; the union cleans overlaps.
-        StrokedShapeGenerator generator = new(strokeOptions);
-        return new ComplexPolygon(generator.GenerateStrokedShapes(outlines, width));
+        return StrokedShapeGenerator.GenerateStrokedShapes(outlines, width, strokeOptions);
     }
 }