Hi Stanislav,
The Krakatoa PRT FumeFX object has a checkbox to generate an Emission channel out of the Fire channel of FumeFX. It basically runs the FumeFX Fire Shader to produce the colors you would expect, but it does nothing for the Smoke color, which ends up being black, unless a Color channel was simulated by FumeFX and exported with the simulation.
In the following simple test, I took a Simple Emitter and let it burn. So not an explosion, but I hope the general principles are the same. I then converted the FumeFX sim to a PRT FumeFX, and checked the checkbox to generate Emission from Fire.
Then I added a Magma modifier to read the Emission and dump into the Color channel so I can visualize what it is producing in the viewports. I then took the Fire channel which describes how much fire there is in the voxel, and used it to Blend an arbitrary Smoke color which I defined as a shade of gray with the Emission color. I also Multiplied by the Density which represents the Smoke channel of FumeFX. In a rendering, the Density would fade off the Smoke Color to transparent, but we don’t support opacity display in Krakatoa PRT objects yet, so I had to fade to black instead. I then clamped the Color between Black and White because Emission can go way above 1.0,1.0,1.0.
I also set the Selection channel to the Density less than a threshold, and used a Krakatoa Delete to cull any particles with low density to control the shape of the resulting plume.
Next I could just make a Frost out of that and enable Vertex Colors - since I am outputting to the Color channel in Magma, that ends up on the mesh!
A material with Vertex Color map would make that then show up in the renderer. The main problem is how to get the Emission as Self-Illumination on the mesh. For that, you can dump the Emission channel to the TextureCoord (mapping 1) channel, and use another Vertex Color Map in the Self-Illumination slot of a Standard material to get the effect into the renderer.
However, a significant part of the volumetric effect is carried by the Smoke/Density information which is mostly lost in this case - we are using it just to dim the color and cull the particles, but the mesh has no transparency whatsoever.
Here I used the TextureCoord to transfer the Smoke info into Opacity, while meshing with Geometry > Custom > Box primitive. (The Box shape in Frost generates its own Mapping Channel 1, which destroys the incoming data from Magma, so I had to make a box in the scene and disable its mapping coordinates).
Without the Opacity data but using the box approach, the effect would look like something out of the LEGO movie!
