Help mimic Fume Black Body Shader with V-Ray Volume Grid / Phoenix shader?

[vfxhooker]

Howdy! So I'm new to Phoenix, and by extension the shader. I've been doing a bunch of Fume explosions and the sims are getting slow to load. I decided to resim and export as open .vdb for use with the v-ray volume grid. After purchasing Phoenix FD, it looks to me like the V-Ray volume grid is using the same basic shader as Phoenix. Maybe slightly different? Anyway, so far, I'm having no luck rendering the vvg fire/smoke in a manner that looks anything even remotely close to my Fume FX. Is there a known formula for being able to closely approximate the black-body shader, etc from Fume with the Phoenix shader setup? Also does anyone have recommendations on a current tutorial or series of tutorials on using the Phoenix shader/rendering options? I love how fast the volume grid is in comparison to the fume sims. Hope I can make it look as good!

Thanks!

[Svetlin.Nikolov]

Hey,

It's exactly the same code for both shaders - the volume grid is the Phoenix shader extracted and wrapped as a V-Ray plugin. It's just different depending on the moment in time Phoenix or V-Ray is built. If you get a Phoenix nightly, you will always be using the latest version

We've attempted to make an automatic conversion script from FumeFX settings to Phoenix/VolumeGrid, but it turned out a lot of stuff happen under the hood with the FumeFX shader and the script remained on hold. So unfortunately you'll have to match the looks manually - here are some tips to keep in mind https://docs.chaosgroup.com/display/...meFXandHoudini

Step by step equalizing the render settings so that you'll get the closest possible match works like that:
- First equalize the smoke alpha. Turn off fire in FFX and set Fire -> 'Based on' to Disabled and work with the Smoke Opacity rollout - if the smoke has a specific render curve in FFX, replicate it in Phoenix. Otherwise you can go with Simple Smoke mode as well. I think the curve in FFX was flipped horizontally for some reason though - note that in Phoenix smoke amount zero is one the left and smoke amount 1 is on the right of the curve. Adjust the opacity until the alpha of the rendered smoke match.
- Second step is equalizing the smoke color, which should be simpler especially in case it's just a constant over the entire volumetric. With the fire still disabled, adjust the smoke color or the smoke color gradient until the RGB renders match.
- The next two steps are with smoke rendering disabled and fire enabled - set Fire -> Based on -> Fuel (by default the FFX fire channel maps to Phoenix's fuel), set the Fire Opacity Mode to Own Opacity, turn off Emit Light, and first equalize the alpha by adjusting the render curve and the fire opacity multiplier. This is very important because fire can have color and opacity in Own Opacity as well, so equalizing the color and alpha simultaneously can be much more difficult than first equalizing the alpha and then the color.
- Finally adjust the fire strength and color gradient according to the ones set in FFX. Here the Physically Based option also takes effect - by default Phoenix uses black body radiation model and with this param you can balance between adding exponential intensity (at 1.0) versus having the fire color look exactly like the one in the color gradient (at 0.0). I suggest that you first zero the Physically Based option and after you match the colors with FFX, try boosting it little by little. A current limitation of Physically Based is that it needs fire to be based on a channel which is in Kelvins, such as the Phoenix Temperature channel which ranges usually from 300 to 2000. If you plug in FFX's fire channel which could go up to 10-20, this will not work and would need to be scaled - this is in our TODO list, so that channels outside the physically correct range would be able to be shaded too. You could still get the black body by manually changing the fire curve to an exponent shape and setting the fire multiplier to a crazy 5-6 digit number though.

Hope this helps - if you have anything in progress and need advise, please ping us

Cheers!

[vfxhooker]

Svetlin,

Thanks so much for replying! I will get into my scene and use your instructions and see what I can come up with. I really appreciate your response.

-Josh