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Combining PyGame and PyCairo

Note: See http://pygame.org/wiki/CairoPygame for other examples.

This piece of code allows you to convert a Cairo surface to a PyGame surface. It also includes a small example on how to make SVG loading work. It works with Python 2.5+ and requires relatively recent versions of pygame, pycairo and NumPy to work. For the SVG example to work, you must also have rsvg installed.

#!/usr/bin/env python
# Copyleft 2010 Niels Serup, WTFPL 2.0. Free software.

### Imports ###
import math
import pygame
import cairo
import numpy
import Image

### Constants ###
width, height = 640, 480


### Functions ###
def draw(ctx):
    ctx.set_line_width(15)
    ctx.arc(320, 240, 200, 0, 2 * math.pi)

    #                   r    g  b    a
    ctx.set_source_rgba(0.6, 0, 0.4, 1)
    ctx.fill_preserve()

    #                   r  g     b    a
    ctx.set_source_rgba(0, 0.84, 0.2, 0.5)
    ctx.stroke()

def bgra_surf_to_rgba_string(cairo_surface):
    # We use PIL to do this
    img = Image.frombuffer(
        'RGBA', (cairo_surface.get_width(),
                 cairo_surface.get_height()),
        cairo_surface.get_data(), 'raw', 'BGRA', 0, 1)

    return img.tostring('raw', 'RGBA', 0, 1)


### Body ###
# Init PyGame
pygame.display.init()
screen = pygame.display.set_mode((width, height), 0, 32)

# Create raw surface data (could also be done with something else than
# NumPy)
data = numpy.empty(width * height * 4, dtype=numpy.int8)

# Create Cairo surface
cairo_surface = cairo.ImageSurface.create_for_data(
    data, cairo.FORMAT_ARGB32, width, height, width * 4)

# Draw with Cairo on the surface
ctx = cairo.Context(cairo_surface)
draw(ctx)


##### SVG LOADING EXAMPLE #####
# Using rsvg it is possible to render an SVG file onto a Cairo
# surface. Uncomment the following lines to make it work.
#import rsvg # This will probably not work in Windows. As far as I
# know, only GNU/Linux distibutions package this Python
# module. Nevertheless, it should be easy to create a small wrapper;
# see http://www.cairographics.org/cairo_rsvg_and_python_in_windows/

# Load the file
#svg_graphics = rsvg.Handle('path/to/file.svg')

# Render the graphics onto your Cairo context
#svg_graphics.render_cairo(ctx)

# To get the SVG file's dimensions before you create a Cairo surface,
# use the following function:
#print svg_graphics.get_dimension_data()
###############################

# On little-endian machines (and perhaps big-endian, who knows?),
# Cairo's ARGB format becomes a BGRA format. PyGame does not accept
# BGRA, but it does accept RGBA, which is why we have to convert the
# surface data. You can check what endian-type you have by printing
# out sys.byteorder
data_string = bgra_surf_to_rgba_string(cairo_surface)

# Create PyGame surface
pygame_surface = pygame.image.frombuffer(
    data_string, (width, height), 'RGBA')

# Show PyGame surface
screen.blit(pygame_surface, (0,0))
pygame.display.flip()

clock = pygame.time.Clock()
while not pygame.QUIT in [e.type for e in pygame.event.get()]:
    clock.tick(30)