Function lighten

pattern/canvas.js:3301–3303

(img1, img2, dx, dy, alpha)

    return blend(SUBTRACT, img1, img2, dx, dy, alpha);
}
function lighten(img1, img2, dx, dy, alpha) {
    return blend(LIGHTEN, img1, img2, dx, dy, alpha);
}
function darken(img1, img2, dx, dy, alpha) {
    return blend(DARKEN, img1, img2, dx, dy, alpha);
}