Blender Git Loki

EEVEE: Light: 2.5D Culling: Initial implementation

This follows closely the implementation of 2.5D tiled light
culling described in the presentation:
"Improved Culling for Tiled and Clustered Rendering"
from Michal Drobot
http://advances.realtimerendering.com/s2017/2017_Sig_Improved_Culling_final.pdf

I chose the tile + Z binning approach for its high depth range support
and low CPU overhead & low memory consumption compared to the cluster
based culling. The cons is that the culling is a bit less precise in
some aspect but it is quite balanced.

The culling is done by the `Culling` object which is templated to easily
be reused for light probes cullg.

The Z-binning process is described starting from slide 20 in the
reference pdf.

I also implemented a debug pass to visualize false negative (light
culled when they shouldn't) and light evaluation density.
This is useful to detect failure case and hotspot. This could be exposed
as a developper only render pass in the future.

Some optimization of the reference implementation requires extensions
not yet added to GPU module and will be added later.