[IngvarH]

Continuing with trying to understand mxvolumetrics in 3ds Max, and a big problem is the lack of documentation for it. To be able to make a material for the thing I must be able to put some reasonable texture-coordinates on it. But all the documentation refers to Maxwell Studio, and has really no relation to the interface for vdb volumetric in 3ds Max. Am I missing something? Is there some hidden documentation for how this is supposed to work in 3ds Max?

Sincerely,

Ingvar H

[Mihai]

I suppose the UV Channel mapping at the end of the MxVolumetric object settings lets you add UVs based on different grids contained in the vdb file. The 3dsmax doc on this extension is too sparse I agree, but lets say your vdb file contained among other grids, one grid named "temperature", you write that in the Additional grids text field (how to find out how many grids a vdb file has, and what their names are is explained in the main vdb docs). And then in the UV Channel Mapping section, you would add a Temperature UV map. I suppose it wouldn't matter if you add a "Temperature" or a "Density" or an "Age" UV map in this case because the values contained in a temperature grid in the vdb would be of scalar type, and there are several scalar type UV maps you can choose from, among them Density, Temperature, Age. The other type of data a vdb grid can contain is of type vector, and that would be vorticity for example.

The only thing I guess you need to get right is in what order you add them to that UV stack, based on in what order you add the names in the "Additional grids". Maybe your vdb file contains both a temperature grid, and a particle age grid. If you wanted to use both of these grids to generate UVs, you would write: temperature,age in the Additional grids field, and then add two UVs in the UV Channel Mapping stack: Temperature, Age. Now in your Maxwell material you can add maps and choose if you want to use channel 1 or channel 2 for it since the exported volumetric would now contain two UV channels.

The reason you also need to specify the name of the additional grids you want to use is that the name of those grids can have arbitrary names, depending on what name the person who created the file chose. You can have "temp" or "t" or "temperature" or "machupicchu"....so the plugin can't know what the names of the grids are, you need to specify that. And then add the corresponding UV map types (scalar or vector type) to use that grid data to drive the UVs.

This is all speculation, but it makes sense to me

[IngvarH]

Thank you very much for your answer. Yes, what you say made sense to me too, and that's what I tried yesterday, but it doesn't work.

I've been testing with the free explosion.vdb, the one used in the documentation. When I render the file, I can see the limits of the temperature data, which I add. I make a gradient, for testing purposes, a horizontal black to red one. The whole explosion becomes black. I test with a horizontal image with the first vertical row of pixels black, the rest red. The explosion becomes all black. So, it doesn't seem as if it's using the texture coordinates at all.

It would have been interesting to be able to test this in Maxwell Studio, but I can't as I only have the 3ds Max plugin.

Any developer with some input on this?

Sincerely

Ingvar Hulterstrom

[Mihai]

What is your Base grid multiplier set to? Leave it at 1 to test the texture with. Also you may need to set the vdb float 00 range to what is contained in the specific vdb file. For the explosion vdb it's 0 - 0.88.

In any case, I'd ask tech support to explain in more detail how it's supposed to work in Max...

[IngvarH]

Yeah...I think it's time for some techsupport. Again, thanks for you help.

\Ingvar H

[IngvarH]

Just a little update. I tried using the first grid,"density", instead of "temperature", and that seems to work.

\Ingvar H

[Mihai]

I looked at the UI for the MxVolumetric in Max and there seems to be missing the fields for entering the min / max values for the grids found in a vdb...It only has the "Extra magnitudes" fields (which I'm guessing have something to do with particle files created by RealFlow and not vdb files), but it's missing the extra "VDB field" UI found in the extension in Studio.

[IngvarH]

Thank you...because that's exactly how it seems to me. The ability to uv-map the extra grids is missing.

This, I think, is a serious bug.