[Bf-cycles] Distance Culling of Lamps?

Zauber Paracelsus zauber at gridmail.org
Tue Feb 3 22:18:27 CET 2015

Would it be possible, through a new lamp setting, to support 
distance-based culling of lamps?  The basic idea is that lamps would not 
be sampled if they are far enough away from the area being sampled, 
thereby cutting down on rendering time.

This can already be done to a degree by using nodes via the Ray Length 
output of the Light Path node, and I find that in complex scenes with 
numerous surfaces and several lamps over a large area, it can reduce 
rendering times by roughly half.

However, there are two flaws with this approach:
1) Ray Length only measures the length of the current ray, meaning it 
could still be sampled despite being a greater distance away.
2) Ray Length is supplied after a bounce is calculated (I think), 
meaning it would not be fully sufficient to stop the lamp from being 

If distance culling for lamps is supported directly within blender, 
however, then it would perhaps unlock larger performance gains because 
it would stop the lamp from being sampled before any bounces are calculated.

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