This is the Heatbug demo app.  The code is very well commented,
so the only thing that needs to be said here is that if you want
to see little pictures (pixmap) running around instead of squares,
then run make like so:

   make CPPFLAGS=-DUSE_PIXMAP

Also, you can write screenshots for each update to PNG files
if you build like this:

   make CPPFLAGS=-DSCREENSHOTS
