implement pre-collapsed shader stage, fix #216

[illwieckz]

This is my attempt to implement pre-collapsed shader stages, as defined in #216.
This will allow to use more than one collapsed (multi-texture) stage per shader.

Historical syntax (Doom3-like) with collapsing heuristic is still there.

[illwieckz]

That looks ready to me

[illwieckz]

I removed the colorMap stage keyword as it is useless and seems to have no reason to be used. In the engine, a colormap is a simple map without anything else (no lightmap, no normal…).

[illwieckz]

I merged into master the very first commit that is not doing anything on the code itself, except moving some text to make subsequent PR less noisy.

[illwieckz]

Note to myself; I said there: #189 (comment)

that I had an implementation to collapse both lighting stages and reflection stages with an unified glsl shader (I hope I still have the branch somewhere 😁 ) but this is blocked because of #190.

Once a fix is found for #190, many lines would be deletable.

[illwieckz]

@slipher: resolved remarks, rebased on master

[slipher]

Code seems all right to me. I don't understand anything about shaders, of course.

[illwieckz]

I don't understand anything about shaders, of course.

Which is unfotunately to expect: that code is probably the most obscure part of dæmon, at least the most obscure I've seen.

Basically XreaL project hacked shader parser of Quake 3 to parse Doom3 shaders the quick and dirty way, expecting multi textures as shader globals (what does Doom 3) while the Quake 3 design allows advanced stage blending and operation. While those textures parts (normal/spec/glow) can perfectly run as separate stages, for performance reason it's better to collapse everything we can to render as must things we can in one pass, hence the convoluted collapse code that has to deal with the fact there is way to define textures both in shader stages and shader globals… 😨

To add features it's usually required to redesign from scratch some parts that do not make possible to extend the existing code to add such features. So, hopefully, PR after PR the code becomes less complex. And less buggy: there is a lot of dragons ready to bite in dark corners, and bugs, those dragons are trained and bugs squished as I walk over the code. It's all about serendipity.