Time for the yearly GPU rant

[savage309]

Well, I feel a remote session would be best. I can open the two scenes that are giving trouble, and you can see what happens. I'm out of ideas. We have teamviewer installed already, as we use it to monitor our rendernodes.

Perfect.
We can do anytime in the next two hours today or anytime tomorrow / during the week.
Please mail to blagovest.taskov@chaosgroup.com with cc to support@chaosgroup.com for what time works for you and for Team Viewer details.

Best,
Blago.

[kosso_olli]

Okay,
I got the scene with the car working by hiding the wheels rear lights. For some reason the material on this makes the render crash, I have no idea why. Maybe I find the time to debug further
So I got my scene rendered in around 25min on a single 1080Ti in 4K.

Sadly I am not pleased with the result because of severe bugs, some of them I have reported over half a year ago! Following are some images to demonstrate.

First of all, here is an image from the same scene in CPU mode. There is no post work to this, this is straight out of the VFB. I know you can't directly compare results, but still, this is what GPU has to fight against.



Now, this is the first result I got with GPU, minus wheels and lights. You can immediately see that there is something wrong with the VRayPlane set to matte shadow catcher. For some strange reason the car is getting illuminated from below, and I can not find the cause for this. Also, the shadow of the car is not showing up in the reflection channel. This looks like this very problem here, where I provided a scene for debugging: https://forums.chaosgroup.com/forum/...ection-channel


The noise on the black plastic of the inner wheel arch lining never clears up. Something is going on there.





Also, note the pink color spill on the license plate. This is caused by the VrayPlane. For some reason, the GlobalIllumination RE is all pink, something I have never seen before in CPU mode. There is a second problem to this: The pink color spill can be seen on the car paint in the GI render element, but not in the Beauty. That is an inconsistency that is not acceptable.

[kosso_olli]

Continuing previous post, because of attachment limit.

Next up are the reflection and lighting channel. The strange illumination from below if nowhere to be found in the render elements. So these do not represent the final beauty RGB. Also not acceptable.
Reflection of the shadow is not present here, which makes believable renders quite hard.







In my opinion there is something terribly wrong with the matte shadow system in GPU. It has been a long time since GPU was introduced, and this is still not working correctly. There shouldn't be any illumination out of nowhere. The shadow that falls onto the plane has to reflect back into any objects that are sitting on the ground plane. And most of all: We need the ground projection feature. This is essential in the automotive visualization field. As I said, that alone is something that stops me from using GPU for serious work.

Just for comparison I made a render without matte shadow system, but of course this is useless because I do not want to see the grey ground plane. Neither diretly below the car, and not in the reflection.



I don't want to sound rude every half a year, but I can assure you that whenever a new major release of V-Ray comes out, I am testing exactly this. And for around 3 years, nothing has changes in that regard. Yes, the speed might have been increased, but still GPU is missing crucial features. Until these things are not fixed, I can't even think of considering GPU for rendering. Too much hassle, too much problems.

Take my word: I will try this next year. I don't get tired of doing this.

Thanks for your time.

[kosso_olli]

The render crashes as soon as the wheels are visible. Can't track it down.

[sherridge101]

I am in exactly the same boat.
The secondary matte feature is essential to our work and something that has been asked for on the GPU, several times, starting over 1 year ago.
All of the speed enhancements etc. are good, along with features like dispersion on the GPU, but the secondary matte feature is high priority for lots of us Automotive guys.

Also, I would like to know the 'There are ways to workaround the secondary matte in post' technique?

Cheers

[sherridge101]

ooh, I've also seen the pink in some render test.

[kosso_olli]

Yeah, I keep running into brick walls all the time on GPU. I don't use it, because for my type of work it is completely broken. I have given numerous hints on what to look out for, yet these problems are completely ignored by the developers. GPU rendering will not happen for us, I'm afraid.

[sherridge101]

Shame, we've got a few GPU's here that we can't use in production. Just need the 'Secondary Matte'

[savage309]

Shame, we've got a few GPU's here that we can't use in production. Just need the 'Secondary Matte'

It seems like it is a thing that many people need. As Update 1 for V-Ray Next is quite close, I think it will not make it into that one, but we will see what we can make for the next one.

Best,
Blago.

[kosso_olli]

Please give us the ability to test this inside out. It is time that this need feature is working 100% correctly.

[savage309]

Please give us the ability to test this inside out. It is time that this need feature is working 100% correctly.

I will make sure that when there is secondary matte support we will ping you to test. It will not make it for Update 1, as we haven't started looking into that yet.

Best,
Blago.

[sherridge101]

Ping me too please.

[Ivan1982]

kosso_olli , i had a good laugh reading trough some of the comments you made

I know what you are experiencing as i was there, it's serious issue you are having but those are easy to avoid as you get familiar with engine, CPU and GPU even though are "compatible" should be treated as separate engines.

1) GPU doesn't like overly complicated shaders and old material nodes (older versions of Vray), if you ever find that some particular material (object) is giving you trouble (crashing or error) you can:

a) Make new shader (it favors new shaders anyhow)

b) Use "Corona converter" trick Vray>Corona back to VrayNext it should revert everything back to Default values as it assigns new material and it will keep your shader settings in general ballpark values, however it will require tuning afterwards.

2) If by any chance you require displacement in scene, make sure it is subdivision method as it is easier to manage memory usage although 3d displacement works much better in Next, it can sometimes go nuts and crash the scene, even decimating geometry is good idea sometimes as geometry don't bother GPU at all.
! And ALWAYS disable displacement in material itself (use modifier instead). !

3) Siger shaders and lot's of other 3rd party material packages are known to create troubles with GPU, make sure you either update library or do trick above.

4) Always resize your textures while you are testing scene to 1k, it will give you general idea of memory usage and what can you expect, make sure to use mipmap for bigger resolution, but keep in mind that you can fit amazing amount of things in 11gb of memory.

5) Reflection, glossiness and bump values often need to be specially adjusted for GPU to produce comparable results you got with CPU, though much less in Next than in 3.6.

6) Make sure windows doesn't update your GPU drivers automatically, and that you install some older version if you are running older GPU like 1080TI, guru3d driver uninstaller and then clean install Nvidia drivers, often some pci issues can pop up and you can see it in event viewer so you maybe need to update MB chipset drivers also if that happens.

7) Optimize scene and remove everything that you do not need, it's not like CPU that will eat trough everything, it is as you know very sensitive ans susceptible to crashes.

Go easy on yourself at first, use something simpler to test out what you are getting, maybe simpler shader scene, benefits vs time you are investing, this is from my experience as i personally had same issues when i was trying first time to switch on GPU.

If you accept that this is separate engine you will need some time to get used to, and that there are few limits you must live without like no caustics or support for certain nodes, scene like that BMW should render in couple of minutes or even faster.

Take care,
Ivan

[kosso_olli]

kosso_olli

Go easy on yourself at first, use something simpler to test out what you are getting, maybe simpler shader scene, benefits vs time you are investing, this is from my experience as i personally had same issues when i was trying first time to switch on GPU.

If you accept that this is separate engine you will need some time to get used to, and that there are few limits you must live without like no caustics or support for certain nodes, scene like that BMW should render in couple of minutes or even faster.

Take care,
Ivan

Well, I am trying to use GPU for production work. I can not go easy, because all our scenes look like this. The screenshot I showed was the most basic thing we do. If GPU can not handle this, it is not usable for us, it is that simple. I can agree with the shading part. There might be somehting in there that GPU doesn't support, but most of the shaders are VrScans. And to this day, basic stuff like shadow catcher with secondary matte doesn't work, which is a major deal breaker for us.
The BMW scene has around 25million polies, and I highly doubt it will get rendered in resolutions above 8K in a matter of minutes...

[sherridge101]

Any progress on the Overrides GPU support. Even if it's just the Background, so we can render the floor reflected back in to the geo?