[Bf-cycles] max bounces

[David Fenner]

maybe it's the structure of the scene itself? that with 3 bounces lots of
rays go crazy? it's only a sun coming through a window (interior lighting).
all diffuse.

2014-11-06 10:00 GMT-03:00 David Fenner <d4vidfenner at gmail.com>:

> 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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