Info on OpenGL support

zsnes/opengl.txt

@@ -0,0 +1,57 @@
+     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
+
+
+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 --