
I think the original post was searching for existing implementations of
f.i. Gouroud-shading of triangles. This is fairly complex to do with plain
X. Simpler shading models are implemented already, f.i. in x3d (ask archie
where to get the latest version).
For Gouroud, a fast implementation will be possible utilizing some extension
only, either MIT-SHM to do the shade in an image and fast update the window
with it, or PEX/OpenGL which should be able to shade themselves. The portable
'vanilla X' way would be to shade in a normal XImage and use XPutImage(),
what would be good enough to do static things as f.i. fractal landscapes
or such stuff.

To speak about POVRay, the X previewer that comes with the original source
package is not that good, especially in speed, protocol-friendlyness and
ICCCM compliance. Have a look on x256q, my own preview code. It is on

141.76.1.11:pub/gfx/ray/misc/x256q/

The README states the points where it is better than xwindow.c from
POVRay 1.0
