Color tracer by user data

[JHåland]

Hi! I came across a problem with the tracer object. I want to color the generated strokes by the parent matrix object.

The parent matrix is colored by a shader effector.

I've tried "curve_id", but seem to only color every trace with one color.

Is there other "id" that can fetch "user data" from the matrix object?

- Jørgen

[peter_horvath]

Can you show your setup? If I understand correctly, you want to color the traces based on the Shader effector of the Matrix object, is that right? Don't think that's going to work, because the spline generated by the Tracer is missing the color information.

[JHåland]

hmm. I see that there are curve color in Redshift, picks the index, and hoped there something similar in Arnold.

[JHåland]

I can share link to the setup. I guess I move the files in one or two days 🙂

https://www.dropbox.com/sh/q7g72zp7izyjjyx/AAAE-M6wRxVpDGPc35iGKL59a?dl=0

[peter_horvath]

Does the RSCurveIDColor attribute return the color from the Matrix object? Because the documentation says it returns a random color:

The RSCurveIDColor attribute will create a random color value for each strand. 

You can generate a random color per strand using the curve_id user data and a random shader. But the color of a parent object is not translated to the Tracer curves currently.

[JHåland]

yes, that adds random color, so sounds about the same. So not picking up color form thee matrix

[peter_horvath]

Alright, I think it's a limitation in Cinema 4D, since the generated splines does not have any color information or any connection to the parent object. You can try xptrails which has a color channel.

[JHåland]

hmm, don't seem to get random strands. I have added the arnold tag with export ids, and use user data rgb, and attribute color_id and connect that to a random node. Don't seem to pickup the color_id

[peter_horvath]

The parameter is called curve_id and load it via a user_data_int shader. Connect it to the integer input of the random shader.

[JHåland]

aha, that works! now I have the index of all the tracer strokes. thanks 🙂 Now I just need to colorize them by the matrix object. hmm. thanks for your help so far 🙂