This document is no longer up-to-date, but is a good start to
understanding how the OpenGL code works for non-filtered modes.
-------------------------------------------------------------------------

     OpenGL is currently only avialable on Linux and via CVS. For the most
part, it works and fairly stable. Please send all comments, suggestions,
and bug fixes to hpsolo@my-deja.com. DO NOT EMAIL THE OTHER DEVELOPERS
SINCE THEY ARE not INVOLVED WITH THIS CODE. And please make sure you've
read through the list of known issues before sending your bug report.


HOW OPENGL RENDERS THE SNES VIDEO BUFFER

    The SNES video buffer has dimensions 288x224 (sometimes 288x239 for
certain games; however I have not come across any). The first 16 and last
16 column of pixels are not displayed (perhaps used as a scrolling
buffer?), so the only important part of the video buffer is the middle
256x224 pixels. The SNES video buffer pointer is vidbuffer. With OpenGL,
only the visible 256x224 pixels are needed and they are cropped into
glvidbuffer. glvidbuffer is then turned into a texture that gets bound to
a QUAD whose size depends on whether ZSNES uses aspect ratio to display
each frame.


HI-RES FILTERS WITH OPENGL

     The video mode selection is taken care of by SDL, including full
screen mode. The current code does not allow for many hi-res filter
options. While it is not difficult to implement the hi-res features using
the current filtering code (in copyvwin.asm), it appears that the code for
copy640x480x16bwin() causes memory corruption and sometimes segfaults when
you exit ZSNES. For this reason, the filters have been left out. You can,
however, add it in yourself by:

     1. allocating enough memory space for glvidbuffer (use realloc)
     2. assign glvidbuffer to the destination pointer SurfBufD (instead of
        surface->pixels)
     3. setting Temp1 to surface->pitch, i.e. Temp1 = 2*SurfaceX
     4. calling copy640x480x16bwin()
     5. correctly binding the glvidbuffer as a texture to a QUAD

There is a old patch that enables these filters and it is located at:
http://www.students.uiuc.edu/~handuong/opengl.patch2


3DFX USERS (VOODOO2 AND OLDER HARDWARE)

     Lord_Nightmare managed to get OpenGL to work on a Voodoo2. Some
things you'll need to do in order to get ZSNES OpenGL to work on your
Voodoo:

     1. Make sure to have the latest Mesa drivers and compile it with
        the following option:

	make -f Makefile.X11 linux-386-glide

	Voodoo2 users might want to use:

	make -f Makefile.X11 linux-386-opt-V2-glide

	since that is optimized for Voodoo2 cards. According the the
	XFree86 website, Voodoo3 users (and later) should have DRI
	support via the tdfx driver so this might not be needed.

     2. When you run ZSNES, make sure to set the environment variable
        MESA_GLX_FX to either w or f (window/full screen). E.g. use

	export MESA_GLX_FX=f

	if you use a bash shell. Theoretically using the w option
	should work, but it not only is slow (5fps) but seems
	broken. Voodoo Rush users might be able to get by.

Note that only the 640x480 full screen mode works on the Voodoo2 cards
so please do not email me about the other video modes. Files which
might be usefull to have before compiling anything:

Device3Dfx, Glide_SDK, Glide_V2 (or Glide_XXXX depending on your card)

I believe Glide 2 is what you want, as Glide 3 doesn't work for older
hardware. Also Device3Dfx may not be implemented the same way for 2.4.x
kernels.


KNOWN ISSUES (AND SOME WORK-AROUNDS)

- after many video mode switches (all windowed), switching to full screen
  then back to window mode cases an SDL parachute exit; try not to use too
  many video mode changes, and restart ZSNES every once in a while if you
  are just testing out video modes

- segfault after having compiled the source -- this might be due to an old
  zguicfg.dat file; delete this and see if the problem gets fixed


TODO

- use something like SDL_GL_UpdateRects with hi-res filters

								-- hpsolo --
