curious observation with RT / CPU workflows

[abowen]

hello guys .

I am wondering in anyone has seen a similar situation

Set up a very simple scene with dome light / vray / vray mtls.
What i am curious about is that i see a slight difference(shadow strength and light intensity) with rendering production vs RTgpu. the difference only shows with vray sun turned 'on' ...meaning i get same results (good) between renders if using only dome light and exr image.
Is this a known bug of some kind of special way vray sun interacts with the scene in cpu vs how it does it wit the gpu

[abowen]

murphys law i guess . i think i found the error in the rt engine used . i was using open cl on nvidia gpu's . switched to cuda and prob seemed to vanish

hopefully this can someone else
Andre

[abowen]

alright . it seems to be a bug . has anyone seen this situation before . meaning rendering w cpu production render is different that rtgpu even if all supported features are used.

[bennyboy]

I've actually had similar problems with Cuda GPUs as well: slightly darker renders. I assumed it had to do with the adaptive DMC settings (optimized for fast AA). I wouldn't mind a little explanation, or a link to one, of how RT is different from the standard production renderer in terms of DMC and AA. Initially, I had the feeling it wasn't intended to be adaptive (I thought the whole point was for it not be adaptive, just dumb brute power), but now I'm not sure - apparently they've made it adaptive, but perhaps it doesn't work quite the same as the CPU, so the settings for the lights and such need to be different...don't know.

[vlado]

Is this a known bug of some kind of special way vray sun interacts with the scene in cpu vs how it does it wit the gpu

Which V-Ray version?

Best regards,
Vlado

[abowen]

vray 3.0 nvidia gpu's , max 2014. .... from my knocking around ,it seems like the dome light integration is perfect and works when this is only exterior light.. but my workflow has a vray sun additionally for stronger shadows... this vray sun light is not being added in RT process. weird !