Deterministic multicore rendering

[cfreude]

Hello,

I would like to deterministically get the same results when using the same seed for sample generation.
However it seems that this only works when using a single core, and as soon as I use multiple cores,
there are differences from one run to the next showing the tile pattern.
My guess is that the scheduler does not guarantee that each thread is processing the same tiles in each run,
which results in different random numbers used for certain tiles in each run.

Is my guess correct?
And what would be the minimal change necessary to ensure a completely deterministic result when using multicore rendering?
I only render locally, so I would not need this for remote rendering on a cluster.

I currently have difficulties understanding the full scheduling infrastructure, since there are numerous interdependent class hierarchies.

Cheers,
Christian

[wjakob]

Hello @cfreude,

no such capability exists at the moment. It might be quite tricky to realize it in an adequately efficient manner, and so that it works on both CPUs and GPUs.

[cfreude]

Dear @wjakob,

thank you for your quick reply.
Since I am using Mitsuba 0.6, it would only need to run on the CPU.
I'll try to see what I can do on that end.
Thank you for confirming my suspicion that it might not be trivial to implement. :)

Cheers,
Christian