int gl_setcontextvga(int mode);
The function returns 0 for success and non-zero if the mode is not supported by the hardware.
The only thing you can do with a planar (mode X-like) 256 color mode is aligned gl_putbox, and use it as a target for gl_copyscreen.
In all of the svga modes this program makes a description of the vga mode available to the vgagl functions. The 256 color svgamodes are handled properly by this program.
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. This page was modified by Don Secrest <email@example.com>.
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.