https://en.wikipedia.org/wiki/GLSL(
DO NOT LINK) h t t p s : / / openarena . wikia . com/wiki/Manual/Graphic_options#GLSL_effects
(
DO NOT LINK) h t t p s : / / openarena . wikia . com/wiki/GLSL (the page is under updating... the updated version is -temporarily- at (
DO NOT LINK) h t t p s : / / openarena . wikia . com/wiki/Glsl_Tutorial_Test).
I hope in future it may be possible to fix a couple of problems that affect 0.8.8 implementation of GLSL shaders when the shader is run with GLSL support disabled or with errors...