From 9e7d16b0a9727d9fd62274f0d98eb0dd0df13a4f Mon Sep 17 00:00:00 2001
From: Evan Hemsley <2342303+ehemsley@users.noreply.github.com>
Date: Sun, 29 Dec 2019 22:54:21 -0800
Subject: [PATCH] optimize rectangle support function

---
 Bonk/Shapes/Rectangle.cs | 41 +++++++++++++++++++++++++++-------------
 1 file changed, 28 insertions(+), 13 deletions(-)

diff --git a/Bonk/Shapes/Rectangle.cs b/Bonk/Shapes/Rectangle.cs
index ebf9a98..5433ecc 100644
--- a/Bonk/Shapes/Rectangle.cs
+++ b/Bonk/Shapes/Rectangle.cs
@@ -38,21 +38,36 @@ namespace MoonTools.Core.Bonk
             AABB = new AABB(minX, minY, maxX, maxY);
         }
 
+        private Vector2 Support(Vector2 direction)
+        {
+            if (direction.X >= 0 && direction.Y >= 0)
+            {
+                return new Vector2(MaxX, MaxY);
+            }
+            else if (direction.X >= 0 && direction.Y < 0)
+            {
+                return new Vector2(MaxX, MinY);
+            }
+            else if (direction.X < 0 && direction.Y >= 0)
+            {
+                return new Vector2(MinX, MaxY);
+            }
+            else if (direction.X < 0 && direction.Y < 0)
+            {
+                return new Vector2(MinX, MinY);
+            }
+            else
+            {
+                throw new ArgumentException("Support vector direction cannot be zero.");
+            }
+        }
+
         public Vector2 Support(Vector2 direction, Transform2D transform)
         {
-            var maxDotProduct = float.NegativeInfinity;
-            var maxVertex = new Vector2(MinX, MinY);
-            foreach (var vertex in Vertices)
-            {
-                var transformed = Vector2.Transform(vertex, transform.TransformMatrix);
-                var dot = Vector2.Dot(transformed, direction);
-                if (dot > maxDotProduct)
-                {
-                    maxVertex = transformed;
-                    maxDotProduct = dot;
-                }
-            }
-            return maxVertex;
+            Matrix4x4 inverseTransform;
+            Matrix4x4.Invert(transform.TransformMatrix, out inverseTransform);
+            var inverseDirection = Vector2.TransformNormal(direction, inverseTransform);
+            return Vector2.Transform(Support(inverseDirection), transform.TransformMatrix);
         }
 
         public AABB TransformedAABB(Transform2D transform)