2d collisions pdf: https://drive.google.com/file/d/1LQhIXwdd0UYjOtahbyL08yf5NxsG6c0I/view?usp=sharing stackoverflow thread: https://stackoverflow.com/questions/345838/ball-to-ball-collision-detection-and-handling vector2d class implementation: http://www.danielsoltyka.com/programming/2010/05/30/c-vector2d-rectangle-classes/