Close the polygons on stroking.

Author: JimBobSquarePants

src/ImageSharp.Drawing/Shapes/OutlinePathExtensions.cs

@@ -49,7 +49,7 @@ public static IPath GenerateOutline(this IPath path, float width, JointStyle joi
         foreach (ISimplePath simplePath in path.Flatten())
         {
             PolygonStroker stroker = new() { Width = width };
-            Polygon polygon = stroker.ProcessPath(simplePath.Points.Span);
+            Polygon polygon = stroker.ProcessPath(simplePath.Points.Span, simplePath.IsClosed);
             polygons.Add(polygon);
         }
 

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

@@ -60,24 +60,45 @@ public double MiterLimitTheta
 
     public double MiterLimit { get; set; } = 4;
 
-    public Polygon ProcessPath(ReadOnlySpan<PointF> pathPoints)
+    public Polygon ProcessPath(ReadOnlySpan<PointF> pathPoints, bool isClosed)
     {
         for (int i = 0; i < pathPoints.Length; i++)
         {
             PointF point = pathPoints[i];
             this.AddVertex(point.X, point.Y, PathCommand.LineTo);
         }
 
-        this.AddVertex(pathPoints[^1].X, pathPoints[^1].Y, PathCommand.LineTo);
-        this.closed = 1;
-        this.Rewind();
+        if (isClosed)
+        {
+            this.AddVertex(0, 0, PathCommand.EndPoly | (PathCommand)PathFlags.Close);
+        }
 
         double x = 0;
         double y = 0;
-        List<PointF> results = new(pathPoints.Length);
-        while (!(_ = this.Vertex(ref x, ref y)).Stop())
+        List<PointF> results = new(pathPoints.Length * 3);
+
+        int startIndex = 0;
+        PointF? lastPoint = null;
+        PathCommand command;
+        while (!(command = this.Vertex(ref x, ref y)).Stop())
         {
-            results.Add(new PointF((float)x, (float)y));
+            PointF currentPoint;
+            if (command.EndPoly() && results.Count > 0)
+            {
+                PointF initial = results[startIndex];
+                currentPoint = new(initial.X, initial.Y);
+                results.Add(currentPoint);
+                startIndex = results.Count;
+            }
+            else
+            {
+                currentPoint = new((float)x, (float)y);
+                if (currentPoint != lastPoint)
+                {
+                    results.Add(currentPoint);
+                    lastPoint = currentPoint;
+                }
+            }
         }
 
         return new Polygon(results.ToArray());