Python GTK+ Canvas

Question

I'm currently learning GTK+ via PyGobject and need something like a canvas. I already searched the docs and found two widgets that seem likely to do the job: GtkDrawingArea and GtkLayout. I need a few basic functions like fillrect or drawline ... In fact these functions are available from c but I couldn't find directions how to use them from python. Can you recommend a tutorial or manpage that deals with their python equivalents ?

If you have a better idea how to get something similar to a canvas every tip would be appreciated. I'm still learning and as long as it can be embedded within my Gtk application I'd be content with any solution.

The apropriate widget for that is GtkDrawingArea. I don't have any sample right now, but you should use pycairo to draw into it, as a reaction to the `expose` event. — rodrigo, Dec 22 '11 at 19:19
That means GtkDrawingArea is only a container that can be filled by other frameworks ? Is there any canvas included in GTK+ ? — lhk, Dec 22 '11 at 19:33
@rodrigo The `expose-event` signal has been replaced by the `draw` signal in gtk3 according to the [reference manual](http://developer.gnome.org/gtk3/3.3/ch25s02.html#id1413935). — jcollado, Dec 22 '11 at 20:00
I read up on pycairo and the possibility to "fill" a drawingarea. It seems like it's possible to let pygame do the job. However common belief is that integrating pygame into gtk+ means trouble: The event systems / update mechanisms crash. I have to admit: As I've already used pygame I'd like to use it again, so I'm a little biased. — lhk, Dec 22 '11 at 20:01
What makes pycairo stand out? @rodrigo why did you recommend it ? — lhk, Dec 22 '11 at 20:01
@lhk - Cairo is pretty much the standard free (as in freedom) 2D graphic library, at least on *nix systems. PyCairo just wraps it. Embedding PyGame in GTK is a -1 for me. :) — mac, Dec 22 '11 at 20:18
@lhk The modern and recommended way to draw in GTK+ is using cairo (the only way in Gtk+3, actually). So if you use PyGTK then using PyCairo is just expected. — rodrigo, Dec 22 '11 at 22:03

rodrigo · Accepted Answer · 2011-12-22T22:28:25.417

In order to illustrate my points made in the comments, let me post a quick'n'dirty PyGtk example that uses a GtkDrawingArea to create a canvas and paints into it using cairo

CORRECTION: you said PyGObject, that is Gtk+3, so the example is as follows (the main difference is that there is no expose event, instead it is draw and a cairo context is already passed as a parameter):

#!/usr/bin/python
from gi.repository import Gtk
import cairo
import math

def OnDraw(w, cr):
    cr.set_source_rgb(1, 1, 0)
    cr.arc(320,240,100, 0, 2*math.pi)
    cr.fill_preserve()

    cr.set_source_rgb(0, 0, 0)
    cr.stroke()

    cr.arc(280,210,20, 0, 2*math.pi)
    cr.arc(360,210,20, 0, 2*math.pi)
    cr.fill()

    cr.set_line_width(10)
    cr.set_line_cap(cairo.LINE_CAP_ROUND)
    cr.arc(320, 240, 60, math.pi/4, math.pi*3/4)
    cr.stroke()

w = Gtk.Window()
w.set_default_size(640, 480)
a = Gtk.DrawingArea()
w.add(a)

w.connect('destroy', Gtk.main_quit)
a.connect('draw', OnDraw)

w.show_all()

Gtk.main()

Ok, the advantages over integrating pygame are more than obvious. The fact that a cairo context is provided with the event is just beautiful. I'll mark this as an answer for the question. Of course I'd appreciate alternative ideas although this seems perfect. — lhk, Dec 23 '11 at 10:23

Python GTK+ Canvas

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