reflect point on line javascript function

README.md

Reflect point along line

Javascript function to reflect point p along line through points p0 and p1. Expects three point objects of the type { x: number1, y: number2 } as input and returns the first point p reflected on p0 and p1 as output.

reflect.js

    /**
     * @brief Reflect point p along line through points p0 and p1
     *
     * @author Balint Morvai <balint@morvai.de>
     * @license http://en.wikipedia.org/wiki/MIT_License MIT License 
     * @param p point to reflect
     * @param p0 first point for reflection line
     * @param p1 second point for reflection line
     * @return object
     */
    var reflect = function(p, p0, p1) {
        var dx, dy, a, b, x, y;

        dx = p1.x - p0.x;
        dy = p1.y - p0.y;
        a = (dx * dx - dy * dy) / (dx * dx + dy * dy);
        b = 2 * dx * dy / (dx * dx + dy * dy);
        x = Math.round(a * (p.x - p0.x) + b * (p.y - p0.y) + p0.x); 
        y = Math.round(b * (p.x - p0.x) - a * (p.y - p0.y) + p0.y);

        return { x:x, y:y };
    }