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Shading problem with yeti fur

Unread postPosted: Tue Jun 30, 2020 11:47 am
by okikoulpa

I'm not really at ease with english for technical explanations, so this is a translation of my message which I wrote with my team in french (it seems that there are maybe some french people who may answer to this question)

We are blocking the assignment of shaders for fur: we imported the cache of fur from maya in the yeti node, as well as the character in alembic with the right UVs. The body is divided into several parts so we use UDIMs for textures. But by plugging the texture of our character on the fur cache, the hairs do not take the texture assigned to them. We use a fur color support plugged in a hair material to project the diffuse of the body on the fur. This technique works when testing with a Clarisse hair generator. But as soon as we want to project on a cache from the procedural yeti the fur goes black.
Do you have a solution to offer us?

In addition is it possible to combine this normal fur support with a gradient to control the color of the hair over its height (root / tip), since these two parameters are connected in the primary and albedo transmission of the hair material?



Nous bloquons sur l'assignation de shaders pour le fur : nous avons importé le cache de fur sorti de maya dans le node yeti, ainsi que le personnage en alembic avec les bons UVs. Le corps est divisé en plusieurs parties nous utilisons donc les UDIM pour les textures. Mais en branchant la texture de notre personnage sur le cache de fur, les poils ne prennent pas la texture qui leur est assignée. Nous utilisons un fur support color branché dans un hair material pour projeter la diffuse du body sur le fur. Cette technique fonctionne quand on fait des tests avec un générateur de hair de Clarisse. Mais dès que nous voulons projeter sur un cache issu du yeti procédural le fur devient noir.
Auriez vous une solution à nous proposer ?

De plus est ce qu’il est possible de combiner ce fur support normal à un gradient pour maitriser la couleur du poil sur sa hauteur (root/tip), puisque ces deux paramètres se branchent dans la primary et transmission albedo du hair material ?

Merci d'avance,

Shading :
Groom :

Re: Shading problem with yeti fur

Unread postPosted: Tue Jun 30, 2020 1:04 pm
by dboude

Fur support color works with UV coordinates. You have to export the UV of the support model within the fur cache. If there are no UV stored it can't work. Basically, you will need two UV sets. One for the individual strand, another for the whole system. Then you will be able to choose which UV set (UV slot in Clarisse) you want to use for mapping. One will control the entire system (the one you want to inject the UDIM in) and the other will control each strand (with this one you will be able to control the root tip mapping, generally you just need the V channel).


Re: Shading problem with yeti fur

Unread postPosted: Tue Jun 30, 2020 1:55 pm
by okikoulpa
Thank you for your answer.
So we have some questions :
- "the UV of the support model" this is a cache of the mesh without the fur, so what's the difference between the base body cache ?
- How can we export the two UV sets ? What do they correspond to ? Do we have to unfold the UVs of the groom into Maya ?
- How can we assign those Uvs to the node Fur Support Color ?

Re: Shading problem with yeti fur

Unread postPosted: Tue Jun 30, 2020 2:17 pm
by dboude
I just tested and yeti export both UV sets you need (by default). And my bad, you don't need the fur color support. This node is just needed when you generate fur with Clarisse generator/interpolate nodes.

Just plug your UDIM stream map file in the color slot of your material and change the UV slot of the stream map file ;)
By default, I have uv_slot_0 for strand UVs and uv_slot_1 for the whole system (the support's UV actually).

Let me know if it works.


Re: Shading problem with yeti fur

Unread postPosted: Tue Jun 30, 2020 2:25 pm
by dboude
Here is an example.

I use the default texture with UV slot 1 which project the color with the UV of the sphere I created fur on (in maya)
And I use a gradient in UV V mode with the UV slot 0 to control the root tip color.



Re: Shading problem with yeti fur

Unread postPosted: Wed Jul 01, 2020 6:39 pm
by okikoulpa
Thans you so much for this quick and clear answer. You allowed us to solve a big problem on wich we spent a lot of time... !

Re: Shading problem with yeti fur

Unread postPosted: Thu Jul 02, 2020 8:33 am
by dboude
You're welcome.