Different cairo operator examples - ported to python from http://stackoverflow.com/questions/9955964/creating-a-highlight-effect-with-the-cairo-library

try_operator.py

import cairocffi as cairo

s = cairo.ImageSurface(cairo.constants.FORMAT_ARGB32, 600, 400)
img = cairo.ImageSurface.create_from_png("/usr/share/icons/gnome/48x48/devices/joystick.png")
w, h = img.get_width(), img.get_height()

cr = cairo.Context(s)

def before():
    cr.save()
    cr.rectangle(0, 0, w, h)
    cr.clip()
    cr.set_source_surface(img)
    cr.paint()

def after():
    cr.restore()
    cr.translate(w, 0)


def try_operator(op, alpha):
    before()
    cr.set_operator(op)
    cr.set_source_rgba(1, 1, 1, alpha)
    cr.paint()
    after()


def try_alpha(alpha):
    cr.save()
    before()
    after()
    try_operator(cairo.constants.OPERATOR_ATOP, alpha)
    try_operator(cairo.constants.OPERATOR_COLOR_DODGE, alpha)
    try_operator(cairo.constants.OPERATOR_SOFT_LIGHT, alpha)
    try_operator(cairo.constants.OPERATOR_HARD_LIGHT, alpha)
    try_operator(cairo.constants.OPERATOR_HSL_HUE, alpha)
    try_operator(cairo.constants.OPERATOR_HSL_SATURATION, alpha)
    try_operator(cairo.constants.OPERATOR_HSL_COLOR, alpha)
    try_operator(cairo.constants.OPERATOR_HSL_LUMINOSITY, alpha)
    cr.restore()
    cr.translate(0, h)


try_alpha(1)
try_alpha(0.75)
try_alpha(0.5)
try_alpha(0.25)
try_alpha(0)

s.write_to_png("/tmp/t.png")