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Daniel dos Orixás avatar image
Daniel dos Orixás asked ·

Smoke and Fire RGBA channels in Turbulence FD to openvdb

Hi

I’m wondering if there is any way to include the ‘fire’ and ‘smoke’ RGBA channels that Arnold uses in its interaction with TFD if you add an Arnold tag to the TFD container, when converting the .bcf files that TFD uses to an OpenVDB format using the bcf2vdb application included with TFD?

Even the command line version states that only the float and vector channels are available, and TFD itself has the same list of channels checkable in the plugin - not the 2 RGBA channels that interact with the Arnold tag on the TFD container and look just like Physical with mutiple scattering. These channels must exist somewhere?!?!

Is there a way to get the 2 RGBA channels included in the OpenVdb conversion? These channels make shading the fire so easy as a starting point!

Many thanks!!


c4dtoavolumes
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Peter Horvath avatar image
Peter Horvath answered ·

Fire and smoke are not actual channels of the simulation, they are shaded results coming from the TFD API. It requires a Turbulence FD Container, does not available in a VDB file. Not sure what you can do, I'd say it's up to TFD and the simulation settings to write out a higher quality VDB. Does the VDB look blocky in other renderers/apps as well?

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Daniel dos Orixás avatar image
Daniel dos Orixás answered ·

Update:

It appears the ‘fire’ channel can be used as a BlackBody multiplier, but if the mode in Arnold is set to ‘channel’ rather than ‘blackbody’ there is a very strange ‘MineCraft’ result…nothing like when those settings are used with the TFD container, which then reproduces the ‘Physical + Multiple Scattering’ look from the native renderer.

Same if you specify ‘smoke’ or ‘density’ in the ‘density’ channel of the openVDB - instant ‘Minecraft’. It has some data to use, but it's...er, odd.

It reports only ‘temperature’ in the ‘available grids’ for the Arnold Volume, so I'm using that for density.

I’m getting some nice looks, just wondering if there is some setup I’m not familiar with that works better.
I'll post some pics when I find some time :)

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Daniel dos Orixás avatar image
Daniel dos Orixás answered ·

Thanks a lot for a super clear answer. No worries, it seems a couple of nodes in the network of the volume shader can do a lot of magic with just that one temperature channel :), and no need to invoke smoke or fire at all.
Just takes a bit of fiddling with ramps and wotnot to zone in on the 'straight from the native TFD shaders' look, which I find a good starting place usually.

I'll have a look to see if I had some intensity settings way out of range, as the dev over at Jawset (TFD) had some useful suggestions about the origins of that blocky look.

But I think basically the TFD container has some good shaders built in (with a bit of tweaking), and it's a matter of starting from scratch if working with a .vdb output of the cache (which is something like 4x the size, also!)

Just learning Arnold atm, and super impressed so far.

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Right, you can definitely achieve something similar with a shader graph, just takes more time. Would be nice having the TFD shader ported as an Arnold shader, but we don't have that atm.
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