Implement per-light Specular property in DirectionalLight3D

[Calinou]

• This closes DirectionalLight3D currently has no Specular property #80737.
• Supersedes Add Specular property to DirectionalLight3D #80742. Thanks @AndrewShobbrook for the original implementation 🙂

[clayjohn]

Looks good to me for RD. I expect a slight performance decrease when using DirectionalLights from this change as I think that part of the shader is relatively load/store bound. However, this was a missing feature so there is no way around it. I would avoid cherry picking this PR for that reason though

For compatibility, have you checked if the property is being sent from the CPU?

[Calinou]

I expect a slight performance decrease when using DirectionalLights from this change as I think that part of the shader is relatively load/store bound.

Can we do bitpacking or use FP16 in the future to reduce the performance impact? This particular value doesn't need much precision, as it's between 0.0 and 1.0 most of the time (rarely above 3.0). Half precision float would be fine, possibly even lower if it's converted from a fixed-point value.

[clayjohn]

Can we do bitpacking or use FP16 in the future to reduce the performance impact? This particular value doesn't need much precision, as it's between 0.0 and 1.0 most of the time (rarely above 3.0). Half precision float would be fine, possibly even lower if it's converted from a fixed-point value.

Bitpacking would most likely help as long as the bottleneck continues to be load/store related. You just need to find a property to pack with it

[Repiteo]

Needs rebase before it can be merged

[Calinou]

Rebased and tested, it works as expected in Forward+/Mobile. I've also managed to fix it in Compatibility (both with shadows enabled and disabled): I was replacing the wrong argument in light_compute() in drivers/gles3/scene.glsl, which is why it wasn't working previously.

While testing this, I've also found that the Specular property doesn't do anything with any light type on vertex-shaded materials. This is an issue on all rendering methods. I believe it should be addressed separately as it'll require more shader changes.

[clayjohn]

While testing this, I've also found that the Specular property doesn't do anything with any light type on vertex-shaded materials. This is an issue on all rendering methods. I believe it should be addressed separately as it'll require more shader changes.

This is intentional. Neither metallic nor specular are used.

[akien-mga]

Thanks!

[Calinou]

This is intentional. Neither metallic nor specular are used.

I meant the light's specular property, not the material's specular property (which is a derivative of its metallic behavior). Light3D Specular only affects the specular lobe (not other reflections), and it should be possible to make it affect vertex-shaded materials too.