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MPM particles / Arnold volume material / Property name changed after "Points_to_volume"

Message 1 of 7
275 Views, 6 Replies

MPM particles / Arnold volume material / Property name changed after "Points_to_volume"


Following the excellent threat about Arnold Volume Material with MPM, I have some issue regarding property color.


Step1 : Sphere with colorset named colorSetBoule




Step 2 : I don't get why I need the "first-in_array" node, as when I dump all the info coming from "granular_particles", I find the same information than those you see with my watchpoint (dump .txt file attached). If you have an answer, to this question, please share it with the basic people I represent here.


Anyway, you can see the property named colorSetBoule is here




Step 3 : after points_to_volume, property name has changed to voxel_colorSetBoule




So I wonder how Bifrost can match the data coming from aiUserDataColor hypershade named colorSetBoule, and this new voxel_colorSetBoule.


Does it make sense ?





So here is the result : color information is missing. But perhaps there is more at stake here than a property name...

What do you think ?




Message 2 of 7
in reply to: moiamy

As this is sampling from a volume, in your shading network you will need to use Arnold's volume_sample_rgb shader (aiVolumeSampleRGB in Maya I think) rather than user_data_color (aiUserDataColor), and set the channel name to voxel_colorSetBoule.  I'm assuming your root shader is a standard volume shader, so you can link the sample volume channel to whatever you'd like such as emission color there to test it out.

Message 3 of 7
in reply to: michael.farnsworth

Thanks for the clue.

I tried but it doesn't work. Same Grey result.

I also tried to put voxel_colorSetBoule in the aiStandardVolume1/Emission Color/channel



Message 4 of 7
in reply to: moiamy

Hm, that should have done at least something for the scatter color.  Your emission mode is set to "none", you might need to change modes for it to pick up the color from the upstream shader node.  Also make sure you set the channel name correctly in the aiVolumeSampleRgb1 node (you probably did).


I'll try this out and see if I can reproduce the missing sampling.

Message 5 of 7
in reply to: michael.farnsworth

Yes it is strange. Even when I tried to use basic color it doesn't work.


But the strangest for me is why we can't plug this aiStandartVolume shader in the volume_material port of the assign_material node....


I have added my file as an attachment.

Message 6 of 7
in reply to: moiamy

Actually it works for aiStandartVolume shader in the volume_material port of the assign_material node.


Just forgot to put voxel_fog_density in Density Channel of the aiStandartVolume shader


But still i can't find a way to use my colorset



Message 7 of 7
in reply to: moiamy

Looks like you are using RGBA (float4) for the colorSet, try changing that to RGB if the intended purpose is to setup colors. 

Also connect the volume shader to the volume_material in the assign_material node. 

You should be able to see colors after these changes.


here is a working example:



Aslan Jafari
Sr QA Analyst

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