Performance drop in VRayDome caused by nodes processed by V-Ray Scene Converter

V-Ray V-Ray for 3ds Max Issues
1

Hi team,

I did some more testing and found the exact trigger for the performance drop.

It turns out the issue is specifically caused by Color Correction nodes that were processed by the V-Ray Scene Converter.

Here are my test results on the exact same scene:

  • VRayDome + Color Correction node (processed by V-Ray Scene Converter): ~5 minutes

  • VRayDome + Newly created Color Correction node (same settings): ~2 minutes

  • VRayDome + Pure HDRI: ~2 minutes

  • Environment Slot (8) + Converted node: ~2 minutes

When using a freshly created node, everything renders fast (~2 mins). However, if the node went through the V-Ray Scene Converter, it leads to a 2.5x render time increase specifically when used inside a VRayDome Light (while rendering normally in the standard Environment slot).

It seems the V-Ray Scene Converter alters internal node parameters or data types in a way that disrupts VRayDome’s Importance Sampling.

Could you please check what the V-Ray Scene Converter modifies in these nodes to cause such a performance hit?

I use this scene with my hdri here:

Thanks!

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2

The performance loss is somewhat expected, and it is due to the fact that there are two such nodes, which add further calculations to your 8K image. The slowdown is apparent with VRayDome, particularly because it contributes to the lighting (unlike the Environment Slot, which affects only GI/Reflections/Refractions).

Simply combine the two nodes into one (as you’ve already done in the screenshot), and you should get better times.

3

No, if i use 1 vray_colorcorrect in dome, my scene still render 5 min.

You can render my scene and be convinced of this. Vray_colorcorrect located in Environment slot.

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Ok, i try render dome with 2 new color correct and get 5 min. But, why if i use it in environment slot i have 2 min?

Now, i render with 1 new color correct and get 5 min with dome.

4

I have answered in the other thread with a simple scene, I think your complicating all settings in your scene, Ill try to test it on later.

5

You are right. I actually reproduced the slowdown without any Color Correction nodes - it seems to be directly linked to the Inverse Gamma calculation. Seems to happen with a .hdr image in your scene, too. Will try to reproduce it on a fresh scene and log it for dev investigation.

EDIT: The problem seems to be not a slowdown, but a negation of the speedup provided by Path Guiding, as the Inverse Gamma render time difference is not apparent without Path Guiding.

6

But if render just inverse gamma 0,5 in environment slot i have 2 min. Just with dome have 5 min. Path Guiding is on.

Path Guiding is off and i still have render with environment faster than dome light.

7

Direct comparison of the Environment slot to the VRayDome is not correct. As I mentioned earlier - VRayDome contributes to the Lighting, unlike the Environment slot.

Otherwise, I managed to reproduce the issue on another scene: Path guiding + VRayDome with a Inverse Gamma corrected Texture = slower rendering. Will log it for dev investigation.

8

Ok, thanks. I have 4 min 20 sec with environment vs 18 min 10 sec with dome light. Path Guiding is off. Just one vraybitmap inverse gamma 0,5. Imposible. I thought a dome light was supposed to be faster.

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9

Logged the issue as (VMAX-15852).

Otherwise, check this thread for more info about the differences between VRayDome Light and the Environment slot.