Rectangle Intersection Test (with C#)

Rectangle Intersection Test (with C#) by Sebastian Krysmanski
http://manski.net/2011/05/rectangle-intersection-test-with-csharp/

/// <summary> 
/// Does axis separation test for a convex quadrilateral. 
/// </summary> 
/// <param name="x1">Defines together with x2 the edge of quad1 to be checked whether its a separating axis.</param> 
/// <param name="x2">Defines together with x1 the edge of quad1 to be checked whether its a separating axis.</param> 
/// <param name="x3">One of the remaining two points of quad1.</param> 
/// <param name="otherQuadPoints">The four points of the other quad.</param> 
/// <returns>Returns <c>true</c>, if the specified edge is a separating axis (and the quadrilaterals therefor don't 
/// intersect). Returns <c>false</c>, if it's not a separating axis.</returns> 
bool DoAxisSeparationTest(Point x1, Point x2, Point x3, Point[] otherQuadPoints) {   
　　Vector vec = x2 - x1;   
　　Vector rotated = new Vector(-vec.Y, vec.X);   
　　bool refSide = (rotated.X * (x3.X - x1.X)                 
　　　　　　　　   + rotated.Y * (x3.Y - x1.Y)) >= 0;   
　　foreach (Point pt in otherQuadPoints) {     
　　　　bool side = (rotated.X * (pt.X - x1.X)                
　　　　　　　　　　+ rotated.Y * (pt.Y - x1.Y)) >= 0;     
　　　　if (side == refSide) {       
　　　　　　// At least one point of the other quad is one the same side as x3. Therefor the specified edge can't be a       
　　　　　　// separating axis anymore.       
　　　　　　return false;     
　　　　}   
　　}   
　　// All points of the other quad are on the other side of the edge. Therefor the edge is a separating axis and   
　　// the quads don't intersect.   
　　return true; 
}