Is it legal to modify the transformation matrices multiple times within the same glBegin()/glEnd() block? Does that bog down the 3D card? I ask this because I have a portion of the map that uses the same texture, and I want to render some of it, change the camera, then render the rest.
Within glBegin/glEnd block, you can not modify any matrix. To do so is an error.
As DFrey said, you can’t do any transformations inside glBegin/glEnd. There is nothing wrong with using multiple glBegin/glEnd blocks in a frame. It’s often even necessary. (A series of triangle strips for example…)