[2.11] Shader changes

[stgatilov]

The latest dev build (dev16617-10107) contains major changes to shaders, which means that the visual look has changed.
The goal of the changes is to remove inconsistency between ambient and interaction, and make TDM lighting math closer to standard Phong (or Blinn-Phong) model which is so familiar to everyone.

1) Now specular term in ambient shader is modulated by specularColor instead of diffuseColor.
The same problem was in interaction shader, and it was fixed back in 2.08 (5044), now the same change is applied to ambient shader for consistency.

2) Specular term in ambient shader is no longer modulated by diffuse texture.
Previously it was additionally modulated by diffuse texture, as if you baked all diffuse textures into specular textures... but only for ambient. In interaction shader, specular term did not depend on diffuse texture (almost --- read below).

3) Directional part of diffuse term in ambient shader is no longer modulated by "(1,1,1) - specular texture color".
This was again some kind of hack against the standard Phong model, not present in interaction shader.

4) Removed dependency of specular term on diffuse texture contents in interaction shader.
Previously there was additional modulation by (75% + 25% * diffuse texture color). On one hand, it was not changing much because 75% of intensity still goes unmodulated. On the other hand, this is again some rather arbitrary hack on top of Phong model.

Overally, I'd say specular has become a bit stronger now.

The main trouble with these changes is of course that they can devastate your carefully tuned assets.
So please report here your experience with the new version.

P.S. The changes were tracked as 5828.