Is Emission working for Volume Medium node?

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Is Emission working for Volume Medium node?

Postby pegot » Thu Sep 15, 2016 6:13 pm

pegot Thu Sep 15, 2016 6:13 pm
I can't seem to get emission working in my smoke sims in Mac Octane Blender.

If I attach an RGB Float texture node to the Emission pin absolutely nothing happens. However if I import the VDB files from Blender into Octane SA I have no problem being able to render Emission.

Wondering if I am doing something wrong in Blender, If this is a bug, or simply a feature not yet fully implemented?
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Re: Is Emission working for Volume Medium node?

Postby JimStar » Thu Sep 15, 2016 7:37 pm

JimStar Thu Sep 15, 2016 7:37 pm
Things are complicated here to explain...

In short.
As I wrote before - Blender currently has a rudimental VDB support internally. So the Octane module uses what works currently, waiting for Blender developers to finish all this.

In long.
Blender saves the VDB files with non-standard channel names. So, standalone opens these files and by default sets the "density" channel to all the Octane channels including "emission". So, because of that, by default you see the "emission" channel "working" - but it renders a wrong data.
But the things are more complicated. Blender exports the channel having this data into a VDB files, with non-standard "heat" or "heat big" names. So, if you choose it manually in standalone for Octane's "emission" channel and this Blender's "heat" channel" will have a meaningful data in it - it should be rendered by standalone.
But the thing here is: Blender only uses this channel internally for any other smoke types than "Domain" (when the "fuel" functionality is active in there). But only "Domain" type supports VDB grids. So, despite the fact Blender tries to save this "heat" channel when generating VDB cache, its code is not finished and the standard functionality of accessing the "flame" grid (that must use the "heat" channel data according what I see in Blender Foundation's code) is not working currently. The Octane module uses Blender's function implied to return the "flame" grid with this data, but currently (in 2.77a) it always returns empty grid (filled by zeroes). Despite the fact the same function implied to return the "density" channel works absolutely OK.
This is the Blender code (Octane-specific) you can see on GitHub:
1.png

You see here that Octane module uses the Blender's function to access the "flame" channel, and it uses this channel as Octane's VDB "emission" channel. But as I said - Blender Foundation's SmokeDomainSettings_flame_grid_get() function always returns the empty "flame" channel for "Domain" type smoke. At the same time SmokeDomainSettings_density_grid_get() works OK and returns actual "density" grid data (used for Octane's scatter and absorption channels).

So, we need to wait before it will be fixed by Blender developers... I could implement this functionality instead of Blender developers, but I can't spend resources developing Blender itself, I only do anything regarding Octane support in it... If I developed this Blender's functionality myself, after Blender developers do the same in the same parts of Blender - merging with a new Blender versions becomes a nightmare 'cause the same functionality in the same Blender files will be developed differently...
So, as I said we need to wait for next Blender versions where the VDB support becomes improved...
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Re: Is Emission working for Volume Medium node?

Postby pegot » Thu Sep 15, 2016 10:18 pm

pegot Thu Sep 15, 2016 10:18 pm
JimStar wrote:As I wrote before - Blender currently has a rudimental VDB support internally. So the Octane module uses what works currently, waiting for Blender developers to finish all this..

That's what I suspected, which is why I didn't post this in the Bugs forum.

Thanks for the explanation, regardless of its complications. At least I don't have to devote more time to figuring out why it didn't work for me. And of course it makes no sense to duplicate Blender developer efforts creating problematic application forks. VDB functionality is still pretty new to Blender; hopefully the necessary development to align it with Octane won't take too long.

Is there a protocol by which Otoy can influence or request from the Blender Foundation such an alignment in regards to VDB?
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Re: Is Emission working for Volume Medium node?

Postby JimStar » Thu Sep 15, 2016 10:38 pm

JimStar Thu Sep 15, 2016 10:38 pm
There is no "alignment" needed... They just need to make the SmokeDomainSettings_flame_grid_get() function working. ;)
As I see currently in their code - the "Domain" smoke object generates the "heat" grid, and this grid is saved to VDB cache. But when it reads this cache (before rendering), it checks and only reads the "heat" channel if the smoke has any other type than "Domain". :shock: So, the "flame" grid (which is supposed to be filled by this "heat" channel data) remains allocated, but not filled in (all values are zeroes) - so when Octane module calls SmokeDomainSettings_flame_grid_get(), it just returns this empty "flame" grid...
So, this looks rather not like a Blender's "bug", but rather like not finished development of this functionality... Where they have made this channel generated for "Domain" smoke, saved to VDB cache, but still not read from this cache to make the SmokeDomainSettings_flame_grid_get() working... This is not just one place in Blender's code where "the bug" could be fixed, this is spread all over different code places as "not finished" code which leads to the consequence that SmokeDomainSettings_flame_grid_get() reads the empty "flame" grid... I don't have a time currently to check if they have already finished this in a trunk, but I hope they will do it at some stage...
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Re: Is Emission working for Volume Medium node?

Postby regionfive » Fri Sep 16, 2016 3:03 pm

regionfive Fri Sep 16, 2016 3:03 pm
I am trying to do some multicolored smoke at the moment. Unfortunately, with octane I cannot access the color attribute from the smoke flow emitter to the shader, like i would do with in the cycles smoke shader. To have multi colored smoke in octane, I would have to set up multiple smoke domains on top of each other. Which works but the simulation doesn´t affect the other smoke emitters and therefore looks odd. Is it somehow possible to write different color information to different VDB Grids within one domain in the Volume Shader?
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Re: Is Emission working for Volume Medium node?

Postby JimStar » Fri Sep 16, 2016 6:54 pm

JimStar Fri Sep 16, 2016 6:54 pm
I already discussed this with haze (developer of Octane's OpenVDB integration), and he said this color information can't be used by Octane's OpenVDB functionality. So, currently I have the obtaining of color data grid implemented in Blender integration, but I've been forced to comment it out 'cause it has no use for Octane rendering core...
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Re: Is Emission working for Volume Medium node?

Postby Synthercat » Sun Dec 17, 2017 7:35 am

Synthercat Sun Dec 17, 2017 7:35 am
Do we have any news about that Blender improvement?
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Re: Is Emission working for Volume Medium node?

Postby JimStar » Sun Dec 17, 2017 7:52 pm

JimStar Sun Dec 17, 2017 7:52 pm
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