opengl: optimization for ati card
This patch is for 1.42 version.
It fixes an important speed issue when using zsnes
opengl frontend with some ati cards under linux. The
problem is that ati driver is really bad at downloading
16 bits (RGB 5-6-5) textures;
after patching, znes does buffer conversion before the
Another change: the texture download now utilizes
glTexSubImage2D instead of glTexImage2D.