In PB, you define fullscreen shaders in the Mod.ini file. Once they are defined, you can swap between different fullscreen shaders (or use shader0, which is to turn them off) on the fly via commands in PB. The command should be listed in the manual somewhere. I also believe I made a note of the command in the Mod.ini file that should be supplied with the PB download. [rummages through old archives] Found it! You use the "SetScreenShader=X" command to swap between them.
There are other shader related commands in there (Such as changing values within the shader itself), but don't have a reference on me to list them off for you right now.
The one and only,
