Correct use of pixbuf, pixmap, and image?

[Ari Jolma <ari jolma tkk fi>]

Hi,

This is about the Gtk2::Ex::Geo modules, which are on CPAN. How the code 
works is, at least partly, explained also on 
http://map.hut.fi/PerlForGeoinformatics

I've got a derivative (subclass in Perl sense) of Gtk2::Gdk::Pixbuf. I 
create it using gdk_pixbuf_new_from_data. The data is created in C using 
my own draw routines. From this pixbuf I create a pixmap by calling 
render_pixmap_and_mask in Gtk-Perl. And in the last step I create an 
Gtk2::Image by calling set_from_pixmap.

The image is used in a subclass of Gtk2::ScrolledWindow. Everything 
works. But there is somewhere a problem of wasting memory.

Creating the initial pixbuf may take a long time (seconds) and it is not 
possible to draw on a pixbuf, only on a pixmap. In my code I want to be 
able to re-use once created pixbuf. For example there is a dialog box, 
where the user may select a graphical object and it is highlighted by 
drawing it (with Gtk-Perl) on the pixmap. So every time the user selects 
a new object, this procedure is executed:

1. create pixmap from the initial pixbuf and set the pixmap into the image
2. draw on the pixmap
3. hide the ScrolledWindow
4. show the ScrolledWindow

I haven't seen a good documentation on some of the functions I use, so 
I've ended up to this procedure with some experimentation. I also don't 
understand well the client/server concept related to this (if the 
program is running over X, the pixmap is created on the client?). I just 
played with this and I believe the code is hogging memory when the above 
procedure is run multiple times. Does anybody have any ideas? About 
documentation.. I just found the Havoc Pennington's book on 
developer.gnome.org and I have Warkus' book. Are there other good sources?

Thanks,

Ari