if (y < y2) {
        k = y < y1 ? 0 : y1 === y2 ? 1 : (y1 - y) / (y1 - y2);
        xa = x1 - (x1 - x2) * k;
        car = c1r - (c1r - c2r) * k;
        cag = c1g - (c1g - c2g) * k;