Add use_texture_arrays project setting for ReflectionProbes

[clayjohn]

Describe the project you are working on

Godot rendering

Describe the problem or limitation you are having in your project

Reflections in reflection probes look significantly worse than reflections from the sky. This is because ReflectionProbes always render their filtered environment maps into a mipmapped cubemap. Skies, on the other hand, by default render their filtered environment maps into texture arrays which are then mipmapped, this results in significantly smoother reflections

Current reflection probe

Current Sky

Describe the feature / enhancement and how it helps to overcome the problem or limitation

This will allow the quality of rough reflections from reflection probes to match the quality of rough reflections from the sky. Using texture arrays comes with an increased cost as you are shading more pixels during the filtering pass and you have to do additional downsample passes to fill the texture array mipmaps, but the quality increase will be worth it, especially for when using Update Mode Once

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

The false here:
https://github.com/godotengine/godot/blob/2a0393e2226d12f077b90e018a1fe4ca171a5562/servers/rendering/renderer_rd/renderer_scene_render_rd.cpp#L762

Will instead change depending on the value of a new project setting reflection_probe_use_texture_array

After drawing, the array mipmaps need to be filled which can be done with a single function as they are done for skies
https://github.com/godotengine/godot/blob/2a0393e2226d12f077b90e018a1fe4ca171a5562/servers/rendering/renderer_rd/renderer_scene_sky_rd.cpp#L1442-L1444

If this enhancement will not be used often, can it be worked around with a few lines of script?

It can't be worked around in script

Is there a reason why this should be core and not an add-on in the asset library?

It is core

[Calinou]

Related to godotengine/godot#49789.

Does this proposal affect objects rendered to the reflection atlas, or just the background sky that is represented on the reflection atlas?

[clayjohn]

Does this proposal affect objects rendered to the reflection atlas, or just the background sky that is represented on the reflection atlas?

Both :) I use the sky as an example in the photos above just so that it is clear how much better the reflections could be.

Related to godotengine/godot#49789.

Yes, but note that this proposal only affects the quality of rough reflections.