First draft of PolygonOffsette

First draft of implementing PolygonOffsetter
Also added back the IntersectionRule to GenerateClippedShapes. It is not implemented yet

Author: stefannikolei

src/ImageSharp.Drawing/Shapes/ClipPathExtensions.cs

@@ -63,7 +63,7 @@ public static IPath Clip(
         clipper.AddPath(subjectPath, ClippingType.Subject);
         clipper.AddPaths(clipPaths, ClippingType.Clip);
 
-        IPath[] result = clipper.GenerateClippedShapes(options.ClippingOperation);
+        IPath[] result = clipper.GenerateClippedShapes(options.ClippingOperation, options.IntersectionRule);
 
         return new ComplexPolygon(result);
     }

src/ImageSharp.Drawing/Shapes/ISimplePath.cs

@@ -1,6 +1,11 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices.ComTypes;
+using SixLabors.ImageSharp.Drawing.Shapes.PolygonClipper;
+using SixLabors.PolygonClipper;
+
 namespace SixLabors.ImageSharp.Drawing;
 
 /// <summary>
@@ -17,4 +22,22 @@ public interface ISimplePath
     /// Gets the points that make this up as a simple linear path.
     /// </summary>
     ReadOnlyMemory<PointF> Points { get; }
+
+    /// <summary>
+    /// Converts to <see cref="SixLabors.PolygonClipper.Polygon"/>
+    /// </summary>
+    /// <returns>The converted polygon.</returns>
+    internal SixLabors.PolygonClipper.Polygon ToPolygon()
+    {
+        SixLabors.PolygonClipper.Polygon polygon = [];
+        Contour contour = new();
+        polygon.Add(contour);
+
+        foreach (PointF point in this.Points.Span)
+        {
+            contour.AddVertex(new Vertex(point.X, point.Y));
+        }
+
+        return polygon;
+    }
 }

src/ImageSharp.Drawing/Shapes/PolygonClipper/Clipper.cs

@@ -19,7 +19,7 @@ internal class Clipper
     /// <param name="operation">The clipping operation.</param>
     /// <param name="rule">The intersection rule.</param>
     /// <returns>The <see cref="T:IPath[]"/>.</returns>
-    public IPath[] GenerateClippedShapes(BooleanOperation operation)
+    public IPath[] GenerateClippedShapes(BooleanOperation operation, IntersectionRule rule)
     {
         ArgumentNullException.ThrowIfNull(this.subject);
         ArgumentNullException.ThrowIfNull(this.clip);
@@ -28,7 +28,6 @@ public IPath[] GenerateClippedShapes(BooleanOperation operation)
 
         SixLabors.PolygonClipper.Polygon result = polygonClipper.Run();
 
-
         IPath[] shapes = new IPath[result.Count];
 
         int index = 0;
@@ -86,15 +85,7 @@ public void AddPath(IPath path, ClippingType clippingType)
     /// <param name="clippingType">Type of the poly.</param>
     internal void AddPath(ISimplePath path, ClippingType clippingType)
     {
-        ReadOnlySpan<PointF> vectors = path.Points.Span;
-        SixLabors.PolygonClipper.Polygon polygon = [];
-        Contour contour = new();
-        polygon.Add(contour);
-
-        foreach (PointF point in vectors)
-        {
-            contour.AddVertex(new Vertex(point.X, point.Y));
-        }
+        SixLabors.PolygonClipper.Polygon polygon = path.ToPolygon();
 
         switch (clippingType)
         {

src/ImageSharp.Drawing/Shapes/PolygonClipper/PolygonOffsetter.cs

@@ -3,6 +3,7 @@
 
 using System.Numerics;
 using System.Runtime.CompilerServices;
+using SixLabors.PolygonClipper;
 
 namespace SixLabors.ImageSharp.Drawing.Shapes.PolygonClipper;
 
@@ -101,13 +102,25 @@ public void Execute(float delta, PathsF solution)
         //
         // // PolygonClipper will throw for unhandled exceptions but if a result is empty
         // // we should just return the original path.
-        // if (solution.Count == 0)
-        // {
-        //     foreach (PathF path in this.solution)
-        //     {
-        //         solution.Add(path);
-        //     }
-        // }
+        SixLabors.PolygonClipper.Polygon result = SixLabors.PolygonClipper.PolygonClipper.Union(this.solution.ToPolygon(), solution.ToPolygon());
+
+        if (result.Count == 0)
+        {
+            foreach (PathF path in this.solution)
+            {
+                solution.Add(path);
+            }
+        }
+
+        foreach (Contour contour in result)
+        {
+            PathF path = new(contour.Count);
+            solution.Add(path);
+            foreach (Vertex vertex in contour)
+            {
+                path.Add(new Vector2((float)vertex.X, (float)vertex.Y));
+            }
+        }
     }
 
     private void ExecuteInternal(float delta)
@@ -680,6 +693,24 @@ public PathsF(int capacity)
         : base(capacity)
     {
     }
+
+    internal SixLabors.PolygonClipper.Polygon ToPolygon()
+    {
+        SixLabors.PolygonClipper.Polygon polygon = [];
+
+        foreach (PathF pathF in this)
+        {
+            Contour contour = new();
+            polygon.Add(contour);
+
+            foreach (Vector2 point in pathF)
+            {
+                contour.AddVertex(new Vertex(point.X, point.Y));
+            }
+        }
+
+        return polygon;
+    }
 }
 
 internal class PathF : List<Vector2>

tests/ImageSharp.Drawing.Tests/Shapes/PolygonClipper/ClipperTests.cs

@@ -39,7 +39,7 @@ private IEnumerable<IPath> Clip(IPath shape, params IPath[] hole)
             }
         }
 
-        return clipper.GenerateClippedShapes(BooleanOperation.Difference);
+        return clipper.GenerateClippedShapes(BooleanOperation.Difference, IntersectionRule.EvenOdd);
     }
 
     [Fact]