Re: Identifying just the one triangle that the user clicked on?

> Doing it with OpenGL:
>
> Assuming you can draw with 8 bits per channel there are 2^24
> values you can address using the colour buffer. Just give each
> triangle a colour that maps to a number, to a glReadPixels on
> the mouse position and you're done.

OUCH!!! What about a 16 bit desktop depth?
DO NOT DO THIS!

You could do it with a gluPickMatrix, but it's not wise either.

> Doing it not with OpenGL:
>
> Use some space partitioning structure to accelerate ray-triangle
> intersection. Or use a ready to use library. Google
> for "collision detection". I can recommend OPCODE
> <http://www.codercorner.com/Opcode.htm>

Best way.
For speed issues, I'd check for a bounding sphere/ray collision first,
this 
can be done very quickly and safes you the triangle-ray test for only a
few 
triangles you would have to investigate further.