Suppose i have a 2d archery game(silly, i know). Player's job is to tap the moving circular archery board. Depending of the accuracy of the tap the player will get a score. More the center is the tap, the more is the score. So, after determining if the tap is within the circle I have to calculate the tap accuracy(by accuracy i mean how close is the tap from the center of the circle) So, how to calculate the distance from the center of the circle to a specific point? .