Some Mesa demos, such as "gloss", render black when running under X without a window manager. With freeglut, the Reshape() function is apparently never called, which is what sets up the frustum and such. Presumably this is because there isn't a window manager to provide a ConfigureNotify event.
Notably, Mark Kilgard's glut does call the Reshape() function.
However, it seems like Mesa demos should probably set up their initial frustum and such.
Works fine with the latest software and running in Xephyr, so don't care I guess. Closing as works for me.