I know the problem, same problem with the X version (Linux, windowed). The problem is first that I didn't write the Windoze (SDL) graphics driver, and also that it is already very slow. If you know about SDL you can look at it.
I may when I have time, also as I have said before doing 'doze stuff is a problem for me.
Anyone knowing about Xlib is also welcome to fix the X11 driver.