We spawn MAX_LIGHTS/32 (currently 8) jobs and
multi-threading is active as soon as we have more
than one light. All jobs work on disjoint buffers
to avoid false sharing between threads.
It’s possible to adjust roughly the number of jobs
by changing the group size (currently 32). However
this also affects vectorization.
With the current parameters, with 256 lights max
we get 8 jobs, and 4 spot-light test / froxel.
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