Add specialization for directional light split blend and fog to mobile renderer.

[DarioSamo]

Optimizes some paths that can be easily derived by looking at the global scene configuration and adds them as specialization constants to the shaders to help eliminated dead code.

• Multiple optional parameters on fog. This takes out at least three branches that are commonly unused with the default configuration.
• Whether to blend directional light PSSM splits together. This takes out an entire chunk of shadow sampling code that goes unused if the feature is unused. This led to a significant improvement when directional lights are used.

AMD Ryzen 7950 HD Integrated GPU
master: ~20.42 ms
more-mobile-scs: ~19.77 ms

---

Contributed by W4 Games. 🍀

[clayjohn]

Looks good to me. I was able to reproduce the performance benefit in a scene with nothing but a light, a sky, and one default cylinder mesh.

[Calinou]

Code looks good to me.

I wonder if this would be relevant to Forward+ as well, although I presume the performance gain will be lower on a dedicated GPU.

[clayjohn]

I wonder if this would be relevant to Forward+ as well, although I presume the performance gain will be lower on a dedicated GPU.

It might be. We really need to take the time and evaluate what specializations to use in the Forward+ renderer.

For mobile, we are finding that removing pretty much every uniform branch is helpful. For Desktop it will be less helpful and therefore the cost of switching PSOs all the time might outweight the benefit. So we need to evaluate it separately.

[Repiteo]

Thanks!