I want to perform collision detection on rotated rectangles.

It's easy when the rectangles aren't rotated:

Code:

boolean isOverlapped(Shape s1, Shape s2) { //is Shape 2 overlapping Shape 1 
  
	  if ((s1.x + s1.w/2) > (s2.x - s2.w/2)) { return true;} //s1 right edge versus s2 left edge
	  else if ((s1.y + s1.h/2) > (s2.y - s2.h/2)) {return true;} //s1 bottom edge verus s2 top
	  else if ((s1.x - s1.w/2) < (s2.x + s2.w/2)) { return true;} //s1 left edge verus s2 right edge
	  else if ((s1.y - s1.h/2) < (s2.y + s2.h/2)) { return true;} //s1 top edge versus s2 bottom edge
else {return false;}
 
}
 

But when rectangles are rotated (I am using pushMatrix() and popMatrix() to rotate), it's hard to know their exact coordinates. Should I "rotate" my test? I can't get this to work. Is there another technique for testing overlap / collision?

good example above!

using Java 'Areas' is also possible in this case

Code:

boolean isOverlapped(Shape s1, Shape s2) 
{
   // create Areas from your Java Shapes
   Area s1Area = new Area(s1);
   Area s2Area = new Area(s2);

  //translate according to the current rotate angle and the shapes position
   AffineTransform s1Transformation = AffineTransform.getRotateInstance(rotateAngle1, s1.x, s1.y);
   s1Area.transform(s1Trans);
   AffineTransform s2Transformation = AffineTransform.getRotateInstance(rotateAngle2, s2.x, s2.y);
   s2Area.transform(s2Trans);

   // test if they overlap
   s1Area.intersect(s2Area);

   if (!s1.isEmpty())
   {
	return true;
   }
   else
   {
	return false;
   }
}