This PR adds world probe baking to Eevee-next. The world is baked to a
cubemap and is used for reflective light in the deferred render pass.
The world probe is baked to a resolution of 2048x2048. In the future this
would become a user facing setting, but wasn't considered essential for
the first implementation.
When updating the world cubemap the world surface shader is reused.
Currently the world surface shader clears many render passes. It was
decided to replace the render passes with dummy textures as the effort
and potential slowdown didn't weigh against the benefit of doing this nicely.
Updating the world reflection probe isn't expected to happen often.
A big difference with Eevee(-legacy) is that the roughness GGX reflection
parameter isn't baked into the texture (as mipmap levels), but is calculated
during shading. This improves accuracy as we don't assume that every
object is an infinitive small sphere. The result has more noise and that
will be tackled after SSR will land.
Pull Request: https://projects.blender.org/blender/blender/pulls/108149
fb38bb9806