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Read Cd attribute from Houdini splines in C4DtoA

21 REPLIES 21
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Message 1 of 22
cassidydodge2
1132 Views, 21 Replies

Read Cd attribute from Houdini splines in C4DtoA

Hi there,

I am trying to read a Cd attribute on alembic splines created in Houdini but can't seem to get it to work in C4DtoA. I have no problem reading the Cd attribute from Houdini particles...


Thanks

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21 REPLIES 21
Message 2 of 22

In theory all attributes, including Cd should be picked up by the Alembic procedural. We'll take a look if there's a bug somewhere. Meanwhile, do you have any errors or warnings in the console log?

Message 3 of 22

Sorry, newbie question — where can I check the console log? Also, would you recommend a user data shader to access the cd attribute? That’s what I have in my setup currently.

Message 4 of 22

Yes, a user data shader should do it.

For the Arnold log:

1623793700070.png



// Stephen Blair
// Arnold Renderer Support
Message 5 of 22

Thank you.

Here's what I'm seeing in the console:screen-shot-2021-06-16-at-12748-pm.png

Message 6 of 22

Looks like the data is not there or invalid. Have to take a look.
Message 7 of 22

Does that mean there’s an issue on the Arnold or Houdini side?

Message 8 of 22

Don't know yet, we have to investigate.
Message 9 of 22

Could we get a simple Houdini scene to see how Cd is being set on the splines?


// Stephen Blair
// Arnold Renderer Support
Message 10 of 22

I'm getting an error when I try to attach the Houdini file to this thread...

Message 11 of 22

You can rename it to a ".txt" file
For example:

maya-arnold-usd-test.hip.txt



// Stephen Blair
// Arnold Renderer Support
Message 12 of 22

Thank you. See the working file attached 🙂


Point_Painting_Basic.txt

Message 13 of 22

I don't have your texture, so I used a test UV grid texture.

It's picking up the colors, but there's no much variation, even in Houdini (so I wonder about the UVs?)

1624305599136.png



// Stephen Blair
// Arnold Renderer Support
Message 14 of 22

Hi Stephen,

Thanks for looking into it for me. I've attached an updated Houdini file as well as my original texture. There was quite a bit of variation between colors (see a screenshot of the Houdini file)... C4D / Arnold just doesn't seem to pick any of it up.


Point_Painting_Basic.txt


Message 15 of 22
Message 16 of 22

Cd is there, but even in Houdini I can't get anything except pale red if I render popnet or trial (see my previous post and screenshots).


1624318798555.png


If I export the ABC from attribfrommap, I get something in C4D too:

1624318865743.png



// Stephen Blair
// Arnold Renderer Support
Message 17 of 22

I think it must have something to do with Arnold reading the Cd attribute from trails specifically. I’ve been able to read particle Cd information from the same setup without any issues (same setup but without trails). I used a TP tag to read the Cd channel for particles... is there anything similar for splines?


As far as not getting color info on the trail object in Houdini, I might be missing an attribute transfer. It was working previously.

Message 18 of 22

Hi there,

I'm still struggling to solve this one... If I convert the Houdini splines into geometry then my color information comes in fine but in doing that the size of the file is unmanageable (as an animation). Arnold / C4D must have difficulty reading the color data from splines specifically.

Any further help would be greatly appreciated.

Thanks so much 🙂

Message 19 of 22

Ok, I looked into this again and I think I've solved the problem.

In the Houdini scene file, the GEO object didn't have Arnold properties (that's why the Cd attribute wasn't exported consistently). I added Arnold properties to the GEO and now it works.

c4dtoa-htoa-cd-attribute.png



// Stephen Blair
// Arnold Renderer Support
Message 20 of 22

Hi Stephen,

Thanks so much for working this through. Will give it a go myself. Just so I know, how do I add Arnold properties in Houdini?

cass

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