For several WIPs now and in 1.40, bilinear interpolation would not enable at all when selected with the sdl/linux port of ZSNES. Big issue since bilinear isn't just for making lowres tolerable on a monitor... it corrects scaling artifacts. However, finally decided to take a look in the source code and found that if you remove lines 269 and 270 from src/linux/gl_draw.c bilinear interpolation works when enabled with no apparent side effects.
Anyway, background:
Slackware linux 10.0
SDL 1.2.6
NVIDIA 1.0-6629 w/ Geforce FX 5900+
Again, I know it's just a hack. I hope somebody can either find the real problem or tell me that I broke more than I fixed.
Bug and Hack fix: Bilinear Interp. not working in linux
Moderator: ZSNES Mods