mate-desktop/mate-desktop — pull request #46 by jasmineaura (2012-12-13 17:19:36+00:00)
Title: [mate-bg] cleanup, refactor, plug possible X client leak(s)

Part of the original code (from gnome-desktop) for setting root pixmap seems very similar to, and may have been adapted from common source:
http://people.debian.org/~lunar/xwpset.c

The original concept all dates back to an Eterm/Esetroot technique that became commonly used (ex. xchat) for window transparency over desktop:
http://www.eterm.org/docs/view.php?doc=ref#trans

Wisdom can be gained from studying various similar implementations
Examples:
https://github.com/derf/feh/blob/master/src/wallpaper.c
http://ag.cs.uvic.ca/static/debian5/sources/blackbox_0.70.1/blackbox-0.70.1.orig/util/bsetroot.cc
http://files.minuslab.net/SetBG.cc