The demo uses a G320x200x256 mode or the one you set with SVGALIB_DEFAULT_MODE.
This demo is part of svgalib and can be found in the demos/ subdirectory of the original svgalib distribution. However, it is not installed in the system by default, s.t. it is unclear where you can find it if your svgalib was installed by some linux distribution. Even then, when you have the demo on your system, you probably won't have the sources s.t. it is only of limited use for you.
In case of any such problem, simply get an svgalib distribution from the net. You even don't need to install it. Just make in the demos/ subdirecty. As of this writing, svgalib-1.2.12.tar.gz is the latest version and can be retrieved by ftp from sunsite.unc.edu at /pub/Linux/libs/graphics and tsx-11.mit.edu at /pub/linux/sources/libs which will most probably be mirrored by a site close to you.
svgalib(7), vgagl(7), libvga.config(5), vga_runinbackground(3), threed(6), accel(6), eventtest(6), forktest(6), fun(6), keytest(6), mousetest(6), scrolltest(6), speedtest(6), spin(6), testaccel(6), testgl(6), testlinear(6), vgatest(6), plane(6), wrapdemo(6)
This manual page was edited by Michael Weller <firstname.lastname@example.org>. The exact source of the referenced demo as well as of the original documentation is unknown.
It is very likely that both are at least to some extent are due to Harm Hanemaayer <H.Hanemaayer@inter.nl.net>.
Occasionally this might be wrong. I hereby asked to be excused by the original author and will happily accept any additions or corrections to this first version of the svgalib manual.