Help a n00b understand shaders!

[Patrick]

So Graf's implementation of custom shaders seems like it could be useful, but unfortunately I don't have a clue how to start using them, or even what could be accomplished with them. So here are some questions in no particular order:

(1) The syntax appears to be GLSL specific. Could one potentially borrow code from other open source graphics programs to achieve certain effects? For example, one effect I'd like to see if it is possible would be to add bloom/HDR to my custom skyboxes.

(2) I think it's a safe assumption that abusing shaders or using them extensively could cause some performance issues? Is this a correct understanding?

(3) I've seen it mentioned that reflective effects could be achieved. Could it also be possible to apply reflective or shiny surfaces to model skins? Could it be possible to make brightmaps for model skins?

(4) Graf has an example shader in GZDoom.pk3 now, can someone give me an idea of what exactly this does?

(5) In general, what are some of the things that can be done with these custom shaders? what are their limitations?

Any links to tutorials, wikis, etc. are appreciated. The ZDoom wiki doesn't seem to have any info ATM. And for my sake, please don't post unless you have something that can answer my questions. I don't want to hear about how you hate gzdoom's new renderer or how it isn't doom anymore.

[Patrick]

Double post :S

So here's a link that contains some files that create a rippling effect on textures using GLSL. I figure I can just move this code into my /shaders directory in my PK3 to create a kind of rippling effect for water surfaces:

http://lists.apple.com/archives/quartzcomposer-dev/2008/Sep/msg00009.html

I havent tried this yet, so I have no idea if this will actually work. I'm not going to have the chance to try this until later tonight. If anyone has the opportunity to try this, or if anyone is familiar enough with GLSL to let me know what I might need to make this work, that would be awesome