fix intersections counting for ellipses

src/SixLabors.Shapes/InternalPath.cs

@@ -19,7 +19,7 @@ namespace SixLabors.Shapes
         /// <summary>
         /// The epsilon for float comparison
         /// </summary>
-        private const float Epsilon = 0.0001f;
+        private const float Epsilon = 0.001f;
 
         /// <summary>
         /// The maximum vector
@@ -234,11 +234,11 @@ namespace SixLabors.Shapes
                     {
                         // 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);
-                        if (side != Side.Same && side == SideOfLine(this.points[next], start, end))
+                        if(side != Side.Same && side == SideOfLine(this.points[next], start, end))
                         {
-                            // same side we don't bother adding the crossing
-                            position--; // move back one and the next hist will replace it
-                            count++;
+                            buffer[position + offset] = point;
+                            position++;
+                            count--;
                         }
                     }
                     else
@@ -254,6 +254,7 @@ namespace SixLabors.Shapes
                     lastPoint = point;
                 }
             }
+
             // don't trim the last point
             if(position > 1 && this.closedPath && buffer[offset].Equivelent(buffer[position + offset -1], Epsilon) )
             {

src/SixLabors.Shapes/Rectangle.cs

@@ -170,7 +170,7 @@ namespace SixLabors.Shapes
         /// <value>
         /// The center.
         /// </value>
-        public Vector2 Center => this.topLeft + (this.bottomRight / 2);
+        public Vector2 Center => (this.topLeft + this.bottomRight) / 2;
 
         /// <summary>
         /// Determines if the specified point is contained within the rectangular region defined by

tests/SixLabors.Shapes.Tests/EllipseTests.cs

@@ -49,5 +49,23 @@ namespace SixLabors.Shapes.Tests
                 Assert.NotNull(p);
             }
         }
-    }
+
+        [Fact]
+        public void ClippingCornerShouldReturn1Points()
+        {
+            var poly = new Ellipse(50, 50, 30, 50);
+            var points = poly.FindIntersections(new Vector2(0, 75), new Vector2(100, 75)).ToArray();
+
+            Assert.Equal(1, points.Length);
+        }
+
+        [Fact]
+        public void AcrossEllipsShouldReturn2()
+        {
+            var poly = new Ellipse(50, 50, 30, 50);
+            var points = poly.FindIntersections(new Vector2(0, 49), new Vector2(100, 49)).ToArray();
+
+            Assert.Equal(2, points.Length);
+        }
+    }       
 }

tests/SixLabors.Shapes.Tests/PolygonTests.cs

@@ -218,7 +218,7 @@ namespace SixLabors.Shapes.Tests
             var intersections = poly.FindIntersections(new Vector2(float.MinValue, 137), new Vector2(float.MaxValue, 137));
 
             // returns an even number of points
-            Assert.Equal(2, intersections.Count());
+            Assert.Equal(4, intersections.Count());
         }
 
 
@@ -245,7 +245,7 @@ namespace SixLabors.Shapes.Tests
             var intersections = simplePath.FindIntersections(new Vector2(float.MinValue, 20), new Vector2(float.MaxValue, 20));
 
             // returns an even number of points
-            Assert.Equal(2, intersections.Count());
+            Assert.Equal(4, intersections.Count());
         }
 
         [Fact]
@@ -280,7 +280,7 @@ namespace SixLabors.Shapes.Tests
             var intersections = poly.FindIntersections(new Vector2(float.MinValue, 300), new Vector2(float.MaxValue, 300));
 
             // returns an even number of points
-            Assert.Equal(0, intersections.Count());
+            Assert.Equal(1, intersections.Count());
         }
 
         [Fact]