UV distortion

[danielsian]

Hi guys, I hope everyone is good.

I'm building a polygon hair and Corona doesn't help me too much in this task, just because the UV distorts when I'm using a low poly model.
See attached a test with Physical Render and Corona.

Physical delivers a non distorted UV.

I know, with more subdivision the problem is not visible, but the intention here is to keep low poly.

Thanks

Version: B1 daily Jun 27 2017 (core 1.7 DailyBuild Jun 26 2017)
Cinema version: CINEMA 4D Studio R18.057 S

[burnin]

Wire frame render + simple test scene would give more info & chance for an easy fix/bypass (similar to what c4d engines do in the back)  ;)

I assume single cut/edge loop (down the middle) should fix this.

[danielsian]

The scene is attached with the texture used.
And yes, probably like I said, more Subdivision atenuate the problem, but no fix it.
And even if a cut fix the distortion, I can't create this cut on each hair, in flat generated hairs.
Actually this is my intention.

Thanks

[burnin]

Oh, sorry, missed it.

Didn't mean to subdivide it per se, but do a simple Loop/Path cut.
eg.
Viewport - Left: C4D Physical shaded; Right: Corona shaded & cut



As you can observe in viewport (OGL) same bad result is shown - large quads are shown as if triangulated (underneath these are tris, thus extra edges = extra seams = extra normals) and UV map is distorted. Problem can also be observed with other engines (PRMan, VRay, Arnold, IRay, Cycles, Indigo, Thea, Unreal...). So it's correcting UVs or adding Loops... unless there is something i missed (again)? Is it made in C4D? If it's from another app consider using tris to export or subdivide after, since game engines walk this way.

Note: Cinema fixes this only internally for its render engines (Standard/AR & Physical, but not in viewport).

[houska]

Hi, unfortunately, this is not possible to fix without support for quads, because you have to interpolate across the whole area of the quad instead of taking it as two triangles. What you could try would be use a different mapping type (e.g. "Flat" or "Spatial"), but of course, this approach would be difficult to animate...

Edit: So the core guys said we might eventually support quads, but it's not in any immediate plans.

[danielsian]

Oh, sorry, missed it.

Didn't mean to subdivide it per se, but do a simple Loop/Path cut.
eg.
Viewport - Left: C4D Physical shaded; Right: Corona shaded & cut



As you can observe in viewport (OGL) same bad result is shown - large quads are shown as if triangulated (underneath these are tris, thus extra edges = extra seams = extra normals) and UV map is distorted. Problem can also be observed with other engines (PRMan, VRay, Arnold, IRay, Cycles, Indigo, Thea, Unreal...). So it's correcting UVs or adding Loops... unless there is something i missed (again)? Is it made in C4D? If it's from another app consider using tris to export or subdivide after, since game engines walk this way.

Note: Cinema fixes this only internally for its render engines (Standard/AR & Physical, but not in viewport).

I never realized before that problem, maybe because I'm not used to render low poly stripes like that, and if I did before (I'm not sure) it was in Standard and Physical Render, so never experienced the issue. BWT thanks for you time and tests.

[danielsian]

Hi, unfortunately, this is not possible to fix without support for quads, because you have to interpolate across the whole area of the quad instead of taking it as two triangles. What you could try would be use a different mapping type (e.g. "Flat" or "Spatial"), but of course, this approach would be difficult to animate...

Edit: So the core guys said we might eventually support quads, but it's not in any immediate plans.

I hope they do that!
Thanks