Detects if the vertex point's x and y are inside of a circle

point-in-circle-test.js

/**
 * Detects if the vertex point's x and y are inside of a circle. Only works with
 * plain symetrical circles, not ovals
 * @link Adapted from http://stackoverflow.com/questions/2212604/javascript-check-mouse-clicked-inside-the-circle-or-polygon#answer-2212678
 * @param {array|number} point Point to test, formatted as [x, y]
 * @param {array|number} circleCenter Center of the circle formatted as [x, y]
 * @param {number} radius Radius of the circle, which calculates as half its with or height
 * @returns {boolean} True if the point is contained in the circle
 */
function pointInCircle (point, circleCenter, radius) {
    var xDif = point[0] - circleCenter[0];
    var yDif = point[1] - circleCenter[1];
    return xDif * xDif + yDif * yDif <= radius * radius;
}