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Mike Fix avatar image
Mike Fix asked ·

XParticles Fire in C4D

I'm trying to figure out how to render fire with X-Particles 4. I'm using the most recent demo of Arnold.

Any help is much appreciated!

x-particles
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Peter Horvath avatar image
Peter Horvath answered ·

I suppose you exported the sim to OpenVDB and use the Arnold Volume object, right?

First of all, make sure you list all needed channels in the Grids field of the Arnold Volume.

Than you just use the fuel channel for the emission and heat for blackbody if you selected that mode.


volume-grids.png (16.7 KiB)
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Aias Kokkalis avatar image
Aias Kokkalis answered ·

@Peter Horvath Yes! That worked! You are amazing Peter! Playing with Xparticles OpenVDB and Arnold alot these days two more questions.

1. The Arnold manual says that the XP Gaseous xparticles shader when assigned on an XPDomain should automatically be translated by Arnold. Has this functionality broken with XParticles 4?

2. The velocity data is also exported in the VDB. And it is not loaded apparently in Arnold as motion blur for the OpenVDB volume object does not work. Am I missing something? I have enabled motionblur both in Arnold settings as well as in the object's Arnold tag.

Thanks again for the immediate and great response Peter

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1. Not that I know of, it should work. If not, please send me a scene and I'll take a look.

2. You have to specify the Velocity grid on the Arnold Volume object and enable motion blur, that should be it. I'm sure if I tested with X-Particles though. Again, if you have a scene, I'll take a look.

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1. The standard/physical renderer renders the Gaseous shader properly if I assign the shader on the xpExplosiaFX object. Arnold does not translate the shader regardless of the object of assignment (xpDomain as per documentation or xpExplosiaFx). Scene: https://drive.google.com/open?id=1SC_0pi8R944cx10FpZcdL-2hIou3sr-d

2. This was my fault. When exporting with xpCache, users must include the Velocity channel both in the Inclusion Tab but also in the kind of hidden and obscure dropdown menu in Object -> Build -> EFX Format tab of the xpCache object.

Thanks again!

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I guess I have to clarify the docs. The gaseous shader is translated to Arnold only if it's assigned to an xpDomain. If it's assigned to an Arnold Volume or the xpExplosiaFX, then it won't work, because the channels in the vdb files are different than in a domain (e.g. smoke vs density). I'll take a look if I can make the shader work with VDBs, but for now you have to use the standard_volume shader in this scene.

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Even if assigned at the xpDomain and not through OpenVDB I still cannot make it to work. The simulation should be cached or the Gaseous shader should "just work" on the xpDomain in realtime? I am attaching a new scene to show you that xpDomain and Gaseous shader do not go along well for me.

xpDomain scene: https://drive.google.com/open?id=1Rytw_lk4MpuSe25E6RtCtJx-wFLIKQm_

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Aias Kokkalis avatar image
Aias Kokkalis answered ·

I am not able to render the fire channel at all @djeison canuto ! Would you please guide me with this? the density channel works for the smoke great either with a volume_sample_float node or straight by filling the density channel. Where exactly do I put the fuel field? emission? temperature? A screenshot would be immensely appreciated as I have been struggling to make the fire appear for the last 2 days. Thank you!

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djeison canuto answered ·

I'm not sure if you figure this out but to get XP fire to show up in Arnold you have to make sure you use the same channel naming convention as Arnold. Fuel > Temperature.

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Peter Horvath answered ·

Btw, a workaround could be to cache your sim with an xpcache set to OpenVDB and render with the Arnold Volume object. As far as I know there is a scale problem, so you have to reduce the size.

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Mike Fix avatar image
Mike Fix answered ·

Thank you!

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Peter Horvath answered ·

I'm not sure about the changes in X-Particles 4, yet it's likely the xp3 SDK is not compatible. I'll contact Insydium and update the integration in a future release.

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