Particles opacity problem

[Anonymous]

Hello I imported colored particles into Maya. here's what I do to get the original particles colors to appear in the Arnoild Material :

- Go to Hypershade
* tab > aiStandardSurface
* Outliner : select file1_1
* aiStandardSurface : RMB > assign to selected objet
* aiStandardSurface : attribute editor : base > weight = 1, specular > weight = 0, geometry > opacity = 1
* TAB > particleSamplerInfo.
* particleSamplerInfo connect RGB PP in aiStandardSurface, input : base Color
- Check the render

However, I can't get my alpha / opacity to work. The original particles have alphas set up. With particleSamplerInfo , I tried to connect the "Opacity PP" to aiStandardSurface, inputs Opacity R, Opacity G, Opacity B. But it does not work, the render becomes all black, WHY?

Thanks

David

[Stephen.Blair]

What do you get when you import particles into Maya? Do you have an nParticles node?

I'm not clear on what's in the scene? Some Houdini Engine node?
And if you export an ASS file, what is in it? Is there opacityPP user data on a points node?

[Anonymous]

Hey Stephen!!

Yes I have in my Maya scene a Houdini asset with a particle node called "file1_0" which is treated by Maya as simple particles.

Maya or Houdini Engine has added a "nucleus1" node.

As for ASS: do you mean I should export from Houdini to an ASS file?

[Stephen.Blair]

@David Saber A particleSampler ends up as an Arnold user data shader.

So for opacityPP:

• Add opacityPP to Arnold > Export Attributes on the nParticleShape
• Clear the Opacity check box for the nParticleShape
• In your shading tree, use a User Data Float to get opacityPP, and connect it to the opacity R, G, and B ports.

[Anonymous]

Ok I got it working, I just had to read more precisly the docs!!!

https://docs.arnoldrenderer.com/display/A5AFMUG/Particles : "OpacityPP with particles will only be exported if the Opacity in the Arnold section of the particleShape is disabled." . So:

- file1_1 > file1_1Shape > part Arnold > default settings : Opaque = checked, Matte = unchecked.

- aiStandardSurface_Sparks > particleSamplerInfo2 > we connect the "Opacity PP" to aiStandardSurface, inputs Opacity R, Opacity G, Opacity B > the render is black.

- file1_1 > file1_1Shape > part Arnold > Opaque = unchecked, Matte = unchecked > the render is visible and the opacity is visible!