Per-light energy gives more control to the user on the final result of
volumetric fog. Specific lights can be fully excluded from volumetric fog
by setting their volumetric fog energy to 0, which improves performance
slightly. This can also be used to prevent short-lived dynamic effects
from poorly interacting with volumetric fog, as it's updated over several
frames by default unless temporal reprojection is disabled.
Volumetric fog shadows now obey Light3D's Shadow Opacity property as well.
The shadow fog fade property was removed as it had little visible impact
on the final scene's rendering.
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