Added RainbowBrush

Helper/GradientHelper.cs

@@ -0,0 +1,53 @@
+using System;
+using System.Drawing;
+
+namespace CUE.NET.Helper
+{
+    public static class GradientHelper
+    {
+        // Based on https://dotupdate.wordpress.com/2008/01/28/find-the-color-of-a-point-in-a-lineargradientbrush/
+        public static float CalculateGradientOffset(PointF startPoint, PointF endPoint, PointF point)
+        {
+            PointF intersectingPoint;
+            if (startPoint.Y.Equals(endPoint.Y)) // Horizontal case
+                intersectingPoint = new PointF(point.X, startPoint.Y);
+
+            else if (startPoint.X.Equals(endPoint.X)) // Vertical case
+                intersectingPoint = new PointF(startPoint.X, point.Y);
+
+            else // Diagnonal case
+            {
+                float slope = (endPoint.Y - startPoint.Y) / (endPoint.X - startPoint.X);
+                float orthogonalSlope = -1 / slope;
+
+                float startYIntercept = startPoint.Y - slope * startPoint.X;
+                float pointYIntercept = point.Y - orthogonalSlope * point.X;
+
+                float intersectingPointX = (pointYIntercept - startYIntercept) / (slope - orthogonalSlope);
+                float intersectingPointY = slope * intersectingPointX + startYIntercept;
+                intersectingPoint = new PointF(intersectingPointX, intersectingPointY);
+            }
+
+            // Calculate distances relative to the vector start
+            float intersectDistance = CalculateDistance(intersectingPoint, startPoint, endPoint);
+            float gradientLength = CalculateDistance(endPoint, startPoint, endPoint);
+
+            return intersectDistance / gradientLength;
+        }
+
+        // Based on https://dotupdate.wordpress.com/2008/01/28/find-the-color-of-a-point-in-a-lineargradientbrush/
+        /// <summary>
+        /// Returns the signed magnitude of a point on a vector
+        /// </summary>
+        private static float CalculateDistance(PointF point, PointF origin, PointF direction)
+        {
+            float distance = (float)Math.Sqrt((point.Y - origin.Y) * (point.Y - origin.Y) + (point.X - origin.X) * (point.X - origin.X));
+
+            return (((point.Y < origin.Y) && (direction.Y > origin.Y)) ||
+                ((point.Y > origin.Y) && (direction.Y < origin.Y)) ||
+                ((point.Y.Equals(origin.Y)) && (point.X < origin.X) && (direction.X > origin.X)) ||
+                ((point.Y.Equals(origin.Y)) && (point.X > origin.X) && (direction.X < origin.X)))
+                ? -distance : distance;
+        }
+    }
+}