[x3d-public] Collect Shader variable documentation links into a single page

[Michalis Kamburelis]

doug sanden wrote:
> M,
> Thanks - Q. is this the page I should be looking at for how to implement plugs?
> http://castle-engine.sourceforge.net/compositing_shaders_doc/html/chapter.implementation.html

Yes, exactly. This page outlines our existing implementation in Castle
Game Engine. The actual source code that implements this is of course
open-source, it's in
https://github.com/castle-engine/castle-engine/blob/master/src/x3d/opengl/castlerendererinternalshader.pas
.

It would be *incredibly* cool to see another implementation of this
concept (to show that it's a solid solution to writing shaders in X3D,
and I believe it is, I use it often for real-life cases (my games...)).
So please, please, please --- if you have any questions or suggestions
do ask:)

Regards,
Michalis