make vector comparison looser for duplicate matching

src/SixLabors.Shapes/Helpers/VectorExtensions.cs

@@ -0,0 +1,35 @@
+// <copyright file="ArrayExtensions.cs" company="Scott Williams">
+// Copyright (c) Scott Williams and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace SixLabors.Shapes
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+    using System.Numerics;
+    using System.Threading.Tasks;
+
+    /// <summary>
+    /// Extensions on arrays.
+    /// </summary>
+    internal static class VectorExtensions
+    {
+        /// <summary>
+        /// Merges the specified source2.
+        /// </summary>
+        /// <param name="source1">The source1.</param>
+        /// <param name="source2">The source2.</param>
+        /// <param name="threshold">The threshold.</param>
+        /// <returns>
+        /// the Merged arrays
+        /// </returns>
+        public static bool Equivelent(this Vector2 source1, Vector2 source2, float threshold)
+        {
+            var abs = Vector2.Abs(source1 - source2);
+
+            return abs.X < threshold && abs.Y < threshold;
+        }
+    }
+}

src/SixLabors.Shapes/InternalPath.cs

@@ -225,7 +225,7 @@ namespace SixLabors.Shapes
                 Vector2 point = FindIntersection(this.points[i], this.points[next], start, end);
                 if (point != MaxVector)
                 {
-                    if (lastPoint == point)
+                    if (lastPoint.Equivelent(point, Epsilon))
                     {
                         // hit the same point a second time do we need to remove the old one if just clipping
                         var side = SideOfLine(this.points[last], start, end);

tests/SixLabors.Shapes.Tests/PolygonTests.cs

@@ -283,5 +283,26 @@ namespace SixLabors.Shapes.Tests
             Assert.Equal(0, intersections.Count());
         }
 
+        [Fact]
+        public void MissingIntersection()
+        {
+            var simplePath = new Polygon(new LinearLineSegment(
+                             new Vector2(10, 10),
+                             new Vector2(200, 150),
+                             new Vector2(50, 300)));
+
+            var hole1 = new Polygon(new LinearLineSegment(
+                            new Vector2(37, 85),
+                            new Vector2(130, 40),
+                            new Vector2(65, 137)));
+
+            var poly = simplePath.Clip(hole1);
+
+            var intersections = poly.FindIntersections(new Vector2(float.MinValue, 85), new Vector2(float.MaxValue, 85));
+
+            // returns an even number of points
+            Assert.Equal(4, intersections.Count());
+        }
+
     }
 }