Re: [Flightgear-devel] Color-shifts for textures

[Renk T. <tho...@jy...>]

Ah, now I understand what Mathias is after:

> That would be ok if this would be optional in the sense that it does not
> impact what is there performance wise. But since this is all runtime  
> configured
> by an uebershader with a lot of uniforms this is not the case. Any  
> additional
> feature done in this way *does* impact everbody in several ways. Any
> additional uniform takes time to be set up in the driver. Any code that  
> is in
> the shader and that cannot be optimized away at *link* time of the  
> shader may
> take registers which affects the partitioning and the amount of paralell
> executed threads in the GPU. At least a notable amount of gpu's on the  
> market can get register set limited at that point.

This paragraph has nothing to do with what is actually happening.

1) The 'ubershader' for _models_  (model-combined-deferred.eff and ubershader.vert/frag) has not been introduced by myself but by "Frederic Bouvier and Gijs de Rooy with major additions and revisions by Emilian Huminiuc and Vivian Meazza 2011" (says so in the shader code). That shader requires to insert <generate> tags into each model which uses normal maps. The shader is optional, i.e. it is not compiled if model shader quality is set to zero. It is configured by a lot of uniforms (really a lot more than I ever used for terrain). 

My own contribution with regard to this shader is just to change the light and fog functions, I did not otherwise alter its design. However, since there's lightmap, reflection map, normal map and dirt map, there are potentially 15 different combinations of dedicated shaders which are not configured by uniforms, it seems to me there may be a maintenance issue to consider and it makes sense to do it that way.

I did not come up with the need to modify each model, that is a property of the original shader. Mathias, you picked the wrong audience.

2) The terrain 'ubershader' (terrain-haze-detailed.vert/frag and terrain-haze-ultra.vert/frag) is my own work. These are two quality levels of procedural *terrain*  texturing with terrain-haze.vert/frag being the 'bare' light scattering framework without any terrain effects, just modifying light and fog.

This shader is very different from the model ubershader and does *not* require any insertion or modification of any model. All of these shaders are only compiled if the respective quality level is actually used and atmosperic light scattering is actually checked.

3) terrain-haze-detailed.vert/frag still has if-clauses linked to quality level in - however the plan (made on this list) is to take them out as I recognize it doesn't help for performance. This has largely been done in terrain-haze-ultra.vert/frag already.

It would have been 5 minutes effort for Mathias to take a look into our effect files to see how all this is actually implemented and to realize that none of the shaders being discussed here is compiled unless this is asked for by the user.  But it would appear his criticism is not based on any understanding of the situation, but just on his interpretation of bits and pieces of messages out of context. So, I will disregard it as unfounded.

Mathias, please next time have a look at what you are against before you start writing. Thanks,

* Thorsten