Shading velour

[sharktacos]

A typical approach to shading velvet or velour fabric is to use something like the VrayFalloff Texture to make the shader brighter at grazing angles. In looking at actual fabric samples I observe that there is something in addition going on. The fabric has a direction due to the "pile" which is comparable to the direction of an animal's fur. So when viewing the fabric at a grazing angle with the piles going down (away from the view) the fabric appears brighter, and conversely when viewing the fabric at a grazing angle with the piles going up (towards the viewer) the fabric appears darker. In other words, the brightness is affected by both the viewing angle and the direction of the piles.

So the "render theory" question is how best to simulate this directionality in the shader, together with the falloff based on viewing angle, to achieve this effect?

[dgruwier]

That's anisotropy. Add a noise or texture to the rotation parameter. Fingerprint and smudge textures work very well for that.

[sharktacos]

Anisotropic highlights just mean that the specular dot gets elongated. That is certainly happening on velvet/velour. However, what anisotropy would not do is getting the directionality of the piles so when viewing the fabric with the piles going down (away from the view) the fabric appears brighter, and conversely when viewing the fabric at a grazing angle with the piles going up (towards the viewer) the fabric appears darker.

The only way I can think to do this is with Vray Fur, which would potentially be pretty render intensive. One solution might be to use the normal RE of a rendered swatch of VrayFur and use that as a normal map on the shader.

[sirio76]

Anisotropic highlights just mean that the specular dot gets elongated. That is certainly happening on velvet/velour. However, what anisotropy would not do is getting the directionality of the piles so when viewing the fabric with the piles going down (away from the view) the fabric appears brighter, and conversely when viewing the fabric at a grazing angle with the piles going up (towards the viewer) the fabric appears darker.

The only way I can think to do this is with Vray Fur, which would potentially be pretty render intensive. One solution might be to use the normal RE of a rendered swatch of VrayFur and use that as a normal map on the shader.

I’m building a velvet shader and by looking at real world fabric the behavior is exactly as you described. Right now I’m building the shader in Corona but it will work the same way in Vray too(Vray is my main production engine), I’m fairly happy with preliminary results but the problem is that it works well only using UV projection, as soon as I switch to cubic the look gets screwed up(sometimes the geometry is too complex to be unwrapped). I’ll post a couple test later.
Anyone here have investigated on this topic?

[sirio76]

Here is an example of the issue, if I use the shader using a properly UV mapped surface works quite well, unfortunately not all of my models can be easily unwrapped and as soon as I use a cubic mapping I get a lot of artifacts since my shader is direction dependent like real velvet. Anybody know how to solve this in Vray?

[kosso_olli]

I’m building a velvet shader and by looking at real world fabric the behavior is exactly as you described. Right now I’m building the shader in Corona but it will work the same way in Vray too(Vray is my main production engine), I’m fairly happy with preliminary results but the problem is that it works well only using UV projection, as soon as I switch to cubic the look gets screwed up(sometimes the geometry is too complex to be unwrapped). I’ll post a couple test later.
Anyone here have investigated on this topic?

Anisotropy always needs good UV-coordinates. One of the biggest drawbacks, but sometimes there is no way around it.