BUG rapport, and please help me understand.

[CLF73]

I have rendered these two images, nothing besides the render engine changed. Default render settings - Bucket - Noise threshold 0,05.

See this comparison.


The brightest of the two are the GPU rendered.
The difference in fullrez (15000x7500) render time is CPU 7 hours, and GPU 2 hours. (AMD Ryzen 5950X16core/64GB RAM/GTX 3090)

1: BUG - Please notice that the procedural noise map, set in world space in the displacement snow layer beneith the floor, change its appearance (seed) dependent on if its GPU vs. CPU.
2: Question - Why does the GPU generated appears to have more burnout. See particular around the left hand text on the back wall? which becomes hard to read.
3: Question - It seems that the GPU looses some refractions, in the machinery on the right hand side, near the back wall (becomes almost completely black)?
4: Oh' and one last thing. (not GPU related) Could you please make the VRay Instancer read the particle ID interger of tyFlow?
As far as I can tell, it is not currently possible to replicate the exact particles out of tyFlow with a VRay instancer. Only random or cycle/sequential is currently possible.


I have included the two pictures in better resolution for better local comparison.

Thank you

[hermit.crab]

1. It's not a bug. It happens because both engines use different Noise map implementations. With V-Ray CPU, the native 3ds Max Noise texture is used, whereas with GPU - our implementation of the Noise map is used (accessed through the VRayPluginNodeTex). The results will be identical if both are rendered in Standalone. To resolve the difference within the host platform, use the VRayPluginNodeTex with the TexNoiseMax plugin.
2. That's hard to say without the scene - maybe you could send it for investigation?
3. Try increasing the Trace Depth (Render Setup> Perf> Utilization) and see if that makes any difference.
4. TyFlow particle systems are not yet supported for VRayInstancer. Maybe you mean pFlow?

EDIT:
Missed the 4th question.

[CLF73]

Aha. thank you for responding.

[CLF73]

I would how ever say, that even though there is a locical explination for the noise map difference. I would think that the majority of your user base, would experience this as another particularity (bug) when switching to the GPU engine.

[CLF73]

Please keep in mind that artist who work under tight deadlines, often don't have time or willingness to go through the process to iron out these kinks.
Among my colleagues, there is an increasing interest in a 100% GPU Engine like Redshift, just out of frustration when the department shifted from Vray CPU to VRay GPU a year ago.

I am sure that RedShift has its own issues and missing abilities, but the thought of a engine, build from the ground up, as a 100% gpu engine seems attractive in principle.
However, with a long background in VRay since the early Betas back around 2002-2003. I would like to support and see this grow to its full potential.

[hermit.crab]

That's true. However, we recommend choosing a render engine and sticking to it. CPU and GPU rendering has different requirements, purposes, and benefits, which should be considered prior to a project's start.

[CLF73]

1. It's not a bug. It happens because both engines use different Noise map implementations. With V-Ray CPU, the native 3ds Max Noise texture is used, whereas with GPU - our implementation of the Noise map is used (accessed through the VRayPluginNodeTex). The results will be identical if both are rendered in Standalone. To resolve the difference within the host platform, use the VRayPluginNodeTex with the TexNoiseMax plugin.
2. That's hard to say without the scene - maybe you could send it for investigation?
3. Try increasing the Trace Depth (Render Setup> Perf> Utilization) and see if that makes any difference.
4. TyFlow particle systems are not yet supported for VRayInstancer. Maybe you mean pFlow?

EDIT:
Missed the 4th question.

Regarding 4:
VRay instancer is able to instance objects based on tyFlow (when tyFlow has the interface enabled) but the VRay instancer can not recognize and replicate the exact particle properties with multiple objects, such as shape, size, pos, rot etc. It is my impression this is possible with Pflow as you imply, using the vray instancer - Particle Interger reader.

However, I think most of us prefer tyFlow over pFlow, so it would be an appreciated feature.
Ibeele has some further explanation here:
https://forum.tyflow.com/thread-1623...articleinteger

04-15-2020, 08:33 AM
Not currently, I've supplied ChaosGroup with my interface a few months ago, now we just have to wait for them to implement it.

[hermit.crab]

Yes, you are correct, it does not work for tyFlow systems. Note that using tyFlow's Particle Object Interface (which is inherent in all particle generators in 3ds max) as a linking method to the VRayInstancer is more of a byproduct phenomenon, meaning there may be issues with it. Otherwise, I've logged an improvement request for the particle integer instancing mode's support (internal bug-tracker id: VMAX-11707).