Would it be possible to add GLError checking to residualvm, or, if there already is a mechanism, how do i activate/use it?

If you're simply enabling error checking for debugging, here is what I would do: (in descending order of convenience)
- Use gDEBugger or AMD CodeXL and break on error
- Use apitrace or Renderdoc and check the error log
- If your OpenGL implementation is new enough or has the right extensions, use the OpenGL debug hooks
- If your OpenGL implementation is open source, put a breakpoint on the function that sets the error flag
- Finally, if nothing else works, patch the code to wrap all OpenGL calls with a wrapper that calls `glGetError`.

@Botje

Thank you, i'll go with the easiest...have yet to find out which, probably apitrace (guess something like this exists on AmigaOS4)

1) i don't have a working debugger (gdb is buggy here)
2) glsnoop (apitrace for AmigaOS) does not display any errors (then again it's alpha)
3) The debug hooks sound interesting, but are beyond my capabilities
4) It is opensource, but i'm nowhere near to add anything or compile a working one myself
5) heh, sure :-/

Guess i'll try to catch something with the buggy debugger

Nope, debugger is buggy

I assume it's an unsupported PixelFormat, since i had something similar lately in ScummVM's BladeRunner engine.