[cubic-bezier-solver]

README.md

a cubic-bezier solver.

cubic-bezier.js

"use strict";

module.exports = function(v1, v2, v3, v4, epsilon){

    var curveX = function(t){

        var v = 1 - t,
            b1 = t * t * t,
            b2 = 3 * t * t * v,
            b3 = 3 * t * v * v,
            b4 = v * v * v;

        return v4.x * b1 + v3.x * b2 + v2.x * b3 + v1.x * b4;
    };

    var curveY = function(t){

        var v = 1 - t,
            b1 = t * t * t,
            b2 = 3 * t * t * v,
            b3 = 3 * t * v * v,
            b4 = v * v * v;

        return v4.y * b1 + v3.y * b2 + v2.y * b3 + v1.y * b4;

    };

    return function(t){

        var x = t, t0, t1, t2, x2;

        t0 = 0; t1 = 1; t2 = x;

        if (t2 < t0) return curveY(t0);
        if (t2 > t1) return curveY(t1);

        while (t0 < t1){
            x2 = curveX(t2);
            if (Math.abs(x2 - x) < epsilon) return curveY(t2);
            if (x > x2) t0 = t2;
            else t1 = t2;
            t2 = (t1 - t0) * 0.5 + t0;
        }

        return curveY(t2);

    };
};