Particle Shader Fog Not Honoring Color Maps In GPU

[Joelaff]

I have a bunch of particles from a PhoenixFDFire sim. I am shading them using the Fog method of PhoenixParticleShader. When I use any Map as a Color Map (checkbox ON) the map does not render in VRay5GPU. I do see the effect in the Building Light Cache stage, but then the image proceeds to fill in without the Color Map. It works in CPU VRay5. (Max2021.1 Win10 PHX June 15 release of 4.2).

Render As Geometry has no effect.

VRayGPU kinda makes me pull my hair out because there are so many limitations not fully documented (I love the warnings in the render window-- at least they tell you about some issues).

I see a similar effect with Bitmap Apertures, by the way. The show up in light cache, but then not in the render.

[Svetlin.Nikolov]

This is great timing - we just implemented Color Map for the Fog mode on V-Ray GPU Will have to pick it to the V-Ray 5 stable nightlies and will ping you when you can grab a latest stable nightly

[Joelaff]

This is great timing - we just implemented Color Map for the Fog mode on V-Ray GPU Will have to pick it to the V-Ray 5 stable nightlies and will ping you when you can grab a latest stable nightly

Oh nice!

I ended up switching to Frost for instancing (it is what I normally prefer, but Frost VRay Instancing does not work right in 2021, and I never got it to work in 2020 either... Thinkbox is not so responsive after their purchase by AWS. Prior to that they were fast at fixes and custom build fixes... Sad.)

Anyway, I would be happy to give it a shot. Thanks.

[Svetlin.Nikolov]

Ping again - For mode Color Map for V-Ray GPU will be working in tomorrow's V-Ray 5 stable nightlies: https://nightlies.chaosgroup.com/mai...ble/stable_5.0

We are also working on implementing the Color Map for Bubbles/Splashes modes.

[Svetlin.Nikolov]

Ah, btw, just a note though - neither of the 4 Phoenix textures - Grid, Particle, Ocean and Foam - is implemented on V-Ray GPU. If you want to use any of those in the Color Map, please ping me so I can raise the priority.

[Joelaff]

While we have no pressing need for the Phoenix textures I could certainly see a need at some point in the future. However, it would depend on the scene. I wouldn’t change the priority based on me, though. Thanks.

VFX is weird work, where we frequently abuse tools, by using them in ways they were not intended. Scenes are either really simple with a few elements, or insanely big with full CG scenes. I’d say only a small percentage are currently renderable in GPU due to technical limitations, or GPU memory limitations.

In this shot, which involves millions of under water bubbles that are transparent, the GPU makes such a huge improvement that we are working hard to make it work. CPU is many hours per frame even on ThreadRippers.

[Svetlin.Nikolov]

The V-Ray GPU Phoenix support still needs a lot of love and lately things have picked up, so hopefully there will be more good news soon Please keep pinging us about anything that pops up - your feedback has been excellent so far!

[Joelaff]

What would be very helpful is a way to control the ALPHA (opacity) of the various ParticleShader modes (Fog, Particle, and Bubbles, etc.). Both in Vray CPU and GPU. I don't see a way to do that.

For now I have gone back to CPU... For instance I would really like to fade the alpha to zero with a distance blending Falloff. I can fade the color, but can't seem to fade the alpha. I believe this means (and render times seem to indicate) that those distant particles still need to be rendered. Whereas if they were transparent (opacity mapped) wouldn't the get culled due to cutoff? I am playing with a Cutter object to cull most of them, but it really would be better if we had control over the alpha.


Since you guys are great about listening to feedback here is some more slightly related stuff:

Also, and correct me if I am wrong, but I don't think Point mode honors Depth of Field. This would be VERY nice, as Depth of Field is pretty critical in VFX. Krakatoa does this by essentially blurring each particle based on the distance from the focal plane and then drawing it into the buffer. (Probably more to it than that, especially with their bokkeh, but based on this concept). It works really well.

Another feature I would love to see if a way to take a set of particles, let's say 1 million. I'd like to have a way to assign 20% of those particles to Fog. Then 60% of those particles to Points, and the rest of them to Bubbles. No two types of shaders use the same particle (so you don't get a point inside a bubble).

Also, can EVERY thing that has a random function (like particle count, etc.) please have a Seed parameter? This is very useful. I'd love to have this in all aspects of Phoenix. The ability to Roll the Dice again is very helpul, and also allows things like Krakatoa's Partitioning. (See their docs... I am pretty sure this parameter MUST be named "seed" for it to work.)

Thanks for listening. I know there is a big list of stuff moving forwards. Just thought I'd throw a few more things out there.

[Joelaff]

Please don't miss my other posting directly above this...

However, I wanted to say thank you to you and the GPU guys/gals too for getting the Color Maps working on Fog with GPU! We may be switching back to GPU for this guy.

[Svetlin.Nikolov]

Yay, thanks very much! Opacity texture map for the Particle Shader is in the TODO list - bumped it's priority and now it's among the top 5%. We have to take special care about skipping particles with mapped opacity of zero, but it should not be too hard. The whole thing's gotta come to CPU first, and then we'll port it to GPU and make sure it's also working with Corona...

I've also been thinking about more powerful ways to select particles - currently the Subgroup options allow for some very simple scenarios where you could set one particle shader to a certain subgroup and another shader - to the opposite. Now that we have the Voxel and Particle tuners, we could use the idea for more advanced particle selection as well...

Let us double check the random seed and also the DOF and will get back to you

[Svetlin.Nikolov]

So just confirming - the random values that determine if a particle would render or not or its size seem to be connected to the following options:
- Count Multiplier
- Size Variation and Size Distribution

Please ping me if I'm missing any option..