Recover topology intersection shading

[Ymauchi]

Someone have a good idea.

As shown in the figure, can the shader ignore the error that the topology intersects?
(Do not shade the Back side.)

Occurs when deforming a very thin object like a wing of a dragon.

topologyerror.zip (97.5 KB)

[svetlozar.draganov]

There are some workarounds that could be used in such cases but all of them have some cons and you will most likely have to give up from Receiving or Casting shadows.
The main problem here is that this is a SSS material, so even if we manage to tell V-Ray to not render faces with inverted normals it will still produce some artifacts in the intersection area.
The other problem is that the overlapped faces will cast shadows over the underlying ones, and the only way to remove those is to either disabled Receive or Cast shadows.

Here is the best result I got with SSS material and with OpacityMat and OverrideMtl with ShadowMtl set to fully transparent shader:

Similar result could be generated with SSS material with Opacity Map and disabled Receive and Cast Shadows:

Scenes:
http://ftp.chaosgroup.com/support/sc…s_override.max
http://ftp.chaosgroup.com/support/sc…st_shadows.max

Things get better with VRayMtl, the artifacts on the intersecting edges are not visible as they were with SSS shader.
Here only Receive Shadows is disabled:

Again we can get the same thing with enabled Receive Shadow but with OvertideMtl with fully transparent shader for the Shadows:

Scenes:
http://ftp.chaosgroup.com/support/sc…ve_shadows.max
http://ftp.chaosgroup.com/support/sc…l_override.max

The best option of course will be to check the geometry before rendering and fix it.
There are so many tools for checking and fixing incorrect geometry nowadays, I am sure that this will not be difficult and time consuming task.

[svetlozar.draganov]

SSS Prepass illumination smooths artifacts but they are still visible with naked eye, at least in this scene.
Maybe if intersection area is not so giant artifacts will be unnoticeable:

[Ymauchi]

hello, Svetlozar
Thanks for a good idea!

interested in an idea how to use OverrideMtl’s Shadow Mtl and Perpendicular / Parallell Opacity.
However, in complex and deforming characters artifacts are still noticeable.

Currently it seems to be only to fix by modeling.

Thank you!

[svetlozar.draganov]

It’s always better have clean topology mesh. Render engines can handle some errors but it not very good idea to count on that since the solution is not always perfect.