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Paolo Giandoso avatar image
Paolo Giandoso asked ·

Maya to Arnold, how to read the Cd color attribute of Packed Houdini Instances (from the Copy to Points node)?

Hi

In Houdini I created a base geometry with packed instances (scales) copied on everyone of its points (I used a "copy to points" node with "Pack and Instance" checked). I assigned color to the scales and the base geometry later on in the stream and promoted the Cd attribute to Vertex.

I exported an .abc file with a ROP Alembic node (I checked "Use Instances when possible" and I tried both "Packed Transform: Deform Geometry" and "Packed Transform: Transform Geometry" since I have no clue of which one to use).

Once I open the file in Maya with the GPU Cache node I use the AI Use Data Color to read the Cd attribute I exported from houdini.

The base geometry render with its vertex colors as it should, but the instances render black. Why?

The GPU cache node has a Make Instance and Use Instance Cache options which I have 0 clues about what they do (nothing changes when I check them or uncheck them).

Is there a way to render the vertex color of the packed instances the same way it is possible to do it with the default not instanced geometries? Or any custom attribute really.

In Mantra I can click on "Use Packed Color" in the principal shader and that does the trick.


arnoldmtoahoudinicolorinstances
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rachid Hadj Abderrahmane avatar image
rachid Hadj Abderrahmane answered ·

After the pack you have to transfer your attribute
tranattr.jpg

than you can use aiUserDataColor in Maya with Cd like this:
abcattr.jpg


tranattr.jpg (18.7 KiB)
abcattr.jpg (223.3 KiB)
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untitled-1.jpgHi

Thanks for helping me with this. I am not sure I understood the 1st step (the second yes).

I have packed the scales (instanced geo) already using the copy to point node, is it necessary to pack everything again with the "pack" node?

Are there any settings I need to specify on the "pack" node and "attribute transfer" node to make it work?

Is the attribute randomize necessary to make the process work? I have colored the instances so that they follow a specific gradient I would prefer not to add randomization if possible.

Thanks again :)

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untitled-1.jpg (693.5 KiB)
rachid Hadj Abderrahmane avatar image
rachid Hadj Abderrahmane answered ·

I can't see the pack node!
can you put your scene somewhere, that I can look at it?
edit: do you have the attributes you want in the last node deleteUnusedAttr?


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Absolutely!

https://drive.google.com/file/d/1P8A_KU256MQfXaeEc_WNuNAu5j1RaygI/view?usp=sharing


PS: Yes, I need the Cd attribute so I did not delete it :) In Maya arnold it is applied correctly to the non instanced parts of the file. Just the instances render black.

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You are right does not seem to work! sorry

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Paolo Giandoso avatar image Paolo Giandoso rachid Hadj Abderrahmane ·

Ugh what a bummer.

Thanks anyway! :)

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