Getting weird black sampling squares in atmospheric pass

[luan_simonin]

Hi, I have an issue with rendering atmospheric (as you can tell by the file linked). I am using a fog effect inside of a V-Ray environment plugged into my ROP. Inside the ROP, I have tried lowering the min shading rate to 1, reducing the noise threshold to very low values, reducing the bucket size, switching the AA filter type to Catmull-Rom, increasing the GI subdivs... Inside the fog effect I've tried reducing the step size, reducing the cutoff threshold, increasing the max steps... All of which help to get rid of this issue in other scenes I have, however in this one nothing does the trick. If anyone has any ideas on solution to fix this problem please do let me know, I'd like to add that it's a problem I have encountered across many different scenes and lighting scenarios, I hope this issue gets fixed in future versions of V-Ray because it's really the only big negative thing about it imo. Thanks in advance, wishing you all a wonderful day!
Luan

[david.anastacio]

Hey,

We've detected something similar with the fog too, and found a workaround to fix it, maybe it also fixes you issue. In the Light Evaluation option i the ROP, switch from Adaptive Lights to Full Evaluation mode.
https://docs.chaos.com/display/VRAYH...ionsTab-Lights

I've already sent the Chaos team a test scene with this issue last week, so it should't be long until this is fixed. But we also found a second issue with the fog, when the camera rays can reach the background, the fog becomes very bad sampled, if there where objects and infinity is not visible, the sampling was fine, to fix this we added a falloff map in distance mode and camera Z to the fog transparency slot and faded the fog away in a far distance.

Best,
David.

[viktor_angelov]

Thank you, david.anastacio for joining the thread. luan_simonin Please, give it a try as proposed, to remove all Adaptive Lights from your scene. If this does not resolve the matter, please, Pack your scene and send it to us to investigate further: http://ftp.chaosgroup.com/support/sc...2_10-18-19.jpg

You can send the scene here or by Submitting a Request to our system: Submit a request

[luan_simonin]

Thank you so much david.anastacio viktor_angelov for the kind help. Turning the light evalutation mode to full and adding the falloff map in the transparency slot of the fog helped to get rid of the problem. The render takes way longer however, but I'm guessing that removing all the lights that aren't affecting the fog but are still being calculated will help fix that, so thank you very much! Hoping for this to be adressed in future updates, but in the meantime this method works well.
Best to you two,
Luan

[david.anastacio]

Glad to help ☺️

Are you by any chance not using GI? In our case the Full light evaluation didn't really add time to the render, but not using GI (Brute Force + LC) took the renders from 10 minutes to an hour, so keep the GI ON, it really helps to speed up the render with many lights, even with Adaptive lights not being used.

Best,
David.

[luan_simonin]

Hmm, that's weird, I do have GI on. However, I set it to Light Cache, for this particular scene it was way slower with Brute Force. That was for the beauty render tho, maybe just for the atmos pass setting it to Brute Force could help speed up render time? In any case, turning off the lights that were not affecting the fog seem to bring back render times back to reasonable values.
Best,
Luan