Feathers, Yeti and hair shader 3.

[LL_Will_J]

Hi Guys,

We are doing a project with birds. We are using Yeti for a feather system. With recent updates to Yeti and Vray we are getting some really promising results. Using the Yeti feather system and Vray Hair shader3 we are getting a lovely look to the feathers.

However the Default Yeti feather is rather limited in terms of shapes you can create. So we are looking at using a combination of yeti feathers for the body and some polygon models/cards for the more detailed and patterned feathers on the wings.

I have used the Vray hair shader to great effect on quiet a few jobs and really like it (especially the transmission effects when its back lit).

But is it possible to use the shader on normal polygon geo? I am thinking about a card with an alpha channel, probably a normal map and a diffuse colour. I would love to get all the transmission properties and spec goodness of the hair shader working seamlessly so I can use both yeti feathers and poly geo and shade them in exactly the same way.

Thanks in advance!

Will

[dgruwier]

Don't know about using hair on polygons, I'm guessing it'll never work well because the hair shader assumes that it's used on small tubes. You can convert Yeti feathers into curves, make your changes, and then use VRayRenderableCurve to render them using the hair shader. That way, they'll render in the same way as the pure Yeti ones.
Only thing I'm not sure about is how UVs work on curves, so I'm not sure if it's possible to texture them which would defeat the purpose.

When we had the same problem, we ended up just getting as close as we could with Yeti feathers, and then doing the last bit of shape details using a transparency map in the hair shader.

Out of curiosity, what effect are you trying to achieve with the feathers that Yeti can't do? There's a feature request thread on the Yeti forums about improving feather modeling, your input would probably be helpful there.

[LL_Will_J]

Thanks for your reply dgruwier,

I think I can get the look of all the feathers pretty close now with Yeti feathers. As I have got to grips a bit more with passing attributes about (IDs, feather_UVW and vray hair_properties).

But I still find it daunting to create the high detail flight feathers along the wing using Yeti feathers. The birds we are working on are very realistic - so we will need individual feathers along the wing for control. Did you manage to get the yeti feathers working with a rig? I literally dont know where to start in how to rig a Yeti feather so that it can twist and have super fine control over the individual wing feathers.

I know the Vray side of things is working well. So this is kind of the wrong forum. But I thought I would ask as you seem to have experience already!

Many thanks

Will

[dgruwier]

I feel your pain, I had a skilled rigger help me figuring it out and it took us a long time to get it working problem free. The way we did it was by creating sets of guide curves for the wing feathers, which we could rig, deform and move as we needed. Then we added a single polygon near the base of the primaries, secondaries and tertiaries respectively and used them as the base meshes in the convert node in Yeti. We used the normal $N from those polygons to control the alignment of the feathers in the instance node, so they were always aligned to the animation of the wings, and their own rotation could be further animated.

Almost anyone who uses Yeti would tell you not to go through Yeti to rig wing feathers, but we ended up doing it anyway for the same reasons you mention. I'd only recommend it if you can't find any other way.

If you search on my username on the Yeti forums, you'll probably find a trove of questions that I asked along the way, some of those should be helpful. If you have any problems, ask on the Yeti forums, there's a lot more combined experience over there and people are happy to help.

[LL_Will_J]

Hehe - I also have a skilled rigger scratching his head over this.

I am gonna look at a shading solution for using polygon feathers. I was thinking I can layer up some shaders to achieve the components that make up the hair shader.

Primary spec - use a normal spec with some anisotropic stretch along the feather (paint the rotation angle along the strands? But is probably hard to control)

Secondary spec - tint a second spec from a colour corrected version of my diffuse material (again maybe with anisotropic effect?)

Transmission - Make this using a SSS setup to nicely take backlighting and try and dial this to match the transmission on the hair shaders on the body feathers.

A high res alpha map for the shape and a blurred version of the alpha to make a bump.

Then custom IDs for everything and let comp fix it!

I'll have a snoop around the yeti forums.

Thanks again for your help.

Will