gecko/layout/style/test/animation_utils.js

function px_to_num(str)
{
    return Number(String(str).match(/^([\d.]+)px$/)[1]);
}

function bezier(x1, y1, x2, y2) {
    // Cubic bezier with control points (0, 0), (x1, y1), (x2, y2), and (1, 1).
    function x_for_t(t) {
        var omt = 1-t;
        return 3 * omt * omt * t * x1 + 3 * omt * t * t * x2 + t * t * t;
    }
    function y_for_t(t) {
        var omt = 1-t;
        return 3 * omt * omt * t * y1 + 3 * omt * t * t * y2 + t * t * t;
    }
    function t_for_x(x) {
        // Binary subdivision.
        var mint = 0, maxt = 1;
        for (var i = 0; i < 30; ++i) {
            var guesst = (mint + maxt) / 2;
            var guessx = x_for_t(guesst);
            if (x < guessx)
                maxt = guesst;
            else
                mint = guesst;
        }
        return (mint + maxt) / 2;
    }
    return function bezier_closure(x) {
        if (x == 0) return 0;
        if (x == 1) return 1;
        return y_for_t(t_for_x(x));
    }
}