[Bf-cycles] max bounces

David Fenner d4vidfenner at gmail.com
Thu Nov 6 14:00:17 CET 2014

Hi Thomas, thanks for the commit yesterday, to control bounces per light,
very nice!!

Been doing some tests here, and I ran into a very strange scenario:

When I have 3 or more max diffuse bounces in global render settings,
reducing per lamp bounces have little to no impact in render times, even if
set to 0 bounces. However, when I have only 2 max diffuse bounces in render
settings, lowering per lamp bounces have a very big impact on render times,
reducing them almost as much as if I lowered global diffuse bounces on the
same quantity. It's like there was some sort of threshold at 2 global
bounces. For example:

(on a simple diff scene with one lamp)

Global Max Diff Bounces = 0
Lamp bounces                 = 0
Render Time: 4.7 sec

Global Max Diff Bounces = 3
Lamp bounces                 = 1024
Render Time: 10 sec

Global Max Diff Bounces = 3
Lamp bounces                 = 0
Render Time: 9.7 sec   (almost the same as before)

Global Max Diff Bounces = 2
Lamp bounces                 = 2
Render Time: 8.5 sec      (lower rendertime thanks to one less bounce)

Global Max Diff Bounces = 2
Lamp bounces                 = 0
Render Time: 4.9 sec       (before it didn't even care, yet for 2 bounces
and below its almost as there where no global bounces)

It's great, with 2 global diff bounces and below the gains of lowering per
lamp bounces are almost as big as if lowering global diffuse bounces, so
having only a few lights with GI can increase your rendertimes amazingly,
however,  with 3 global diff bounces and over there is strangely almost no
gain, even when all lamps have 0 bounces.
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