trianglePoints.js

(function () {
    var deg120 = Math.PI * 2/3;
    var deg240 = Math.PI * 4/3;
    var cos120 = Math.cos(deg120);
    var sin120 = Math.sin(deg120);
    var cos240 = Math.cos(deg240);
    var sin240 = Math.sin(deg240);

	/**
	 * Given center and radius of circumcircle, return points of triangle's vertices
	 * @param {Number} x
	 * @param {Number} y
	 * @param {Number} radius
	 * @return {[[Number]]}
	 */
    function trianglePoints (x, y, radius) {
        var c = [x, y + radius];
        
        var bx = c[0] * cos120 - c[1] * sin120;
        var by = c[0] * sin120 + c[1] * cos120;
        
        var ax = c[0] * cos240 - c[1] * sin240;
        var ay = c[0] * sin240 + c[1] * cos240;
        
        return [c, [bx, by], [ax, ay]]
    }
    
    return trianglePoints;
}());