util.js

function deltaTransformPoint(matrix, point) {

    var dx = point.x * matrix.a + point.y * matrix.c + 0;
    var dy = point.x * matrix.b + point.y * matrix.d + 0;
    return { x: dx, y: dy };
}

function decomposeMatrix(matrix) {

    // @see https://gist.github.com/2052247

    // calculate delta transform point
    var px = deltaTransformPoint(matrix, { x: 0, y: 1 });
    var py = deltaTransformPoint(matrix, { x: 1, y: 0 });

    // calculate skew
    var skewX = ((180 / Math.PI) * Math.atan2(px.y, px.x) - 90);
    var skewY = ((180 / Math.PI) * Math.atan2(py.y, py.x));

    return {

        translateX: matrix.e,
        translateY: matrix.f,
        scaleX: Math.sqrt(matrix.a * matrix.a + matrix.b * matrix.b),
        scaleY: Math.sqrt(matrix.c * matrix.c + matrix.d * matrix.d),
        skewX: skewX,
        skewY: skewY,
        rotation: skewX // rotation is the same as skew x
    };
}