If you do use the fb device for some reason you don't need to have the user give the screen parameters like size and bit depth. Once you know the name of the framebuffer device all of that information is available in /sys/class/graphics/fbX/
There's also FBIOGET_VSCREENINFO / FBIOPUT_VSCREENINFO through which you can set the current screen information. You can also do fake double buffering this way, by allocating a mode that's twice as tall, drawing to different parts of it, and changing the yoffset to present each "buffer".
