Enter an x and y coordinate for the stationary circle (white) and the other circle can be controlled by mouse x and y. The moving circle turns red on colliding and purple on not colliding. -Mathematical Principles- 1. This works on the principle that the distance between the center of a circle and any point on the circle is equal (radius) and that 2 X Radius is equal to the diameter of the circle. 2. The detection works using the distance formula of coordinate geometry. This engine is free to use with credit to me.