This uses the principles outlined in
Screen Space Indirect Lighting with Visibility Bitmask
to compute local and distant diffuse lighting.
This implements it inside the ray-tracing module as a fallback when the
surface is too rough. The threshold for blending between technique is
available to the user.
The implementation first setup a radiance buffer and a view normal
buffer. These buffer are tracing resolution as the lighting quality is
less important for rough surfaces. These buffers are necessary to avoid
re-projection on a per sample basis, and finding and rotating the
surface normal.
The processing phase scans the whole screen in 2 directions and outputs
local incomming lighting from neighbor pixels and the remaining
occlusion for everything that is outside the view.
The final steps filters the result of the previous phase while applying
the occlusion on the probe radiance to have an energy conserving mix.
Related #112979
Pull Request: https://projects.blender.org/blender/blender/pulls/114259
3097d5d821