We used to use OpenGL, but we had trouble with compatibility so rbz made it use DirectDraw instead.
I can fish out the old code, but it's still dependent on Windows initialisation. Easy enough to fix if it moved to use glut.
Effectively tiny_ptc_ext is there exactly so we can do pixel bashing/software rendering in FB without worrying about DirectX, OpenGL or any of the other stuff. It provides a framebuffer and a way of moving it up to the screen.
Jim