Not Even My Wife Reads This

Someone on the PyGTK mailing list just asked which is faster for drawing rectangles, GDK or Cairo.

I wasn't sure, so I wrote a silly little test program.  Note that it's not quite apples-to-apples as the Cairo rectangles have variable transparency while the GDK rectangles are opaque.

On my box, running Gentoo Linux and the latest stable versions of everything, the Cairo version draws 500 rectangles in about 0.01 to 0.03 seconds, while the GDK version takes about 0.13 to 0.14 seconds.  So Cairo is faster.

To run this, just cut-and-paste into an editor window, save the file as rectangles.py, and run "python rectangles.py"

#!/usr/bin/env python

"""GTK rectangle drawing speed test, GDK vs. Cairo

David Ripton 2008-12-03
MIT license
"""

import time
import random

import gtk

NUM_RECTS = 500

handle_id = None

def main():
    window = gtk.Window()
    window.connect("destroy", gtk.main_quit)
    window.set_default_size(800, 600)
    vbox = gtk.VBox()
    window.add(vbox)
    area = gtk.DrawingArea()
    vbox.pack_start(area)
    gdk_button = gtk.Button("GDK")
    gdk_button.connect("clicked", on_gdk_button_clicked, area)
    vbox.pack_start(gdk_button, expand=False)
    cairo_button = gtk.Button("Cairo")
    cairo_button.connect("clicked", on_cairo_button_clicked, area)
    vbox.pack_start(cairo_button, expand=False)
    window.show_all()
    gtk.main()

def on_gdk_button_clicked(button, area):
    global handle_id
    if handle_id is not None:
        area.disconnect(handle_id)
    handle_id = area.connect("expose-event", on_area_exposed_gdk)
    area.queue_draw()

def on_cairo_button_clicked(button, area):
    global handle_id
    if handle_id is not None:
        area.disconnect(handle_id)
    handle_id = area.connect("expose-event", on_area_exposed_cairo)
    area.queue_draw()

def on_area_exposed_gdk(area, event):
    t0 = time.time()
    width, height = area.window.get_size()
    colormap = area.get_colormap()
    gc = area.get_style().fg_gc[gtk.STATE_NORMAL]
    for ii in xrange(NUM_RECTS):
        r = random.randrange(0, 65535 + 1)
        g = random.randrange(0, 65535 + 1)
        b = random.randrange(0, 65535 + 1)
        gc.foreground = colormap.alloc_color(r, g, b)
        x = random.randrange(0, width)
        y = random.randrange(0, height)
        w = random.randrange(0, width - x)
        h = random.randrange(0, height - y)
        area.window.draw_rectangle(gc, True, x, y, w, h)
    t1 = time.time()
    print "gdk drew %d rectangles in %f seconds" % (NUM_RECTS, t1-t0)

def on_area_exposed_cairo(area, event):
    t0 = time.time()
    cr = area.window.cairo_create()
    width, height = area.window.get_size()
    for ii in xrange(NUM_RECTS):
        r = random.random()
        g = random.random()
        b = random.random()
        a = random.random()
        cr.set_source_rgba(r, g, b, a)
        x = random.randrange(0, width)
        y = random.randrange(0, height)
        w = random.randrange(0, width - x)
        h = random.randrange(0, height - y)
        cr.rectangle(x, y, w, h)
        cr.fill()
    t1 = time.time()
    print "cairo drew %d rectangles in %f seconds" % (NUM_RECTS, t1-t0)

if __name__ == "__main__":
    main()

Rant: It is way too hard to post code with WordPress. First I tried the "code" button, but all my indentation was destroyed (bad for any code, fatal for Python). Then I tried the "b-quote" button; same effect. Then I switched to HTML mode and hand-inserted a "pre" tag, which preserved the indentation. But WordPress then proceded to vandalize my code with "smart" quotes. (Have you ever seen anything with "smart" in its name that actually was?) Luckily it was simple to find and install the wpuntexturize plugin, a few lines of PHP that eradicate Moron Quotes. But why the hell are they there in the first place, let alone enabled by default, let alone enabled by default inside a "pre" tag?