Significance of shaded polygon? (ZBrush)

I’m trying to use Blender with ZBrush.

Sometimes, (when I’m desperate) I export OBJ files from ZB in order to use the UV
editor in Blender. It’s usually because I forgot to assign UVs earlier.

But I find it’s next to impossible to re-export an OBJ from blender and get the vertex
order preserved, even when I make no edits to the mesh whatsoever, and I’m careful
to use the OBJ exporter options to keep vertex order. One or two polys usually have
the vertex order rotated (or flipped) on export.

I’ve noticed that the messed up polys are usually the poly that Blender displays shaded
(see attachment) and possibly one other next to it.

I’m wondering what the significance of this shaded poly’ is, and is there a way to remove
or disable whatever that special quality is to blender?

Does anyone out there have any advice on that, or any help using Blender to UV
meshes from ZB?




The shaded poly is just the active face, the last face selected, you cannot remove it. If you get flipped polys while exporting just flip them back in zbrush or use display double sided polys.

Thanks Richard.

I figured the shading was something like that.

The problem though, is that the re-imported poly’s normals look good back in ZBrush.

The effect on re-import to ZB seems to be that the polys UV assignment gets rotated
or flipped and the texture then displays incorrectly on the affected poly’s (even if the
texture is generated in ZB). It’s as if the texture normal is reversed, but not the
display normal (I don’t have to flip or use ‘double’ to see the affected poly’s in ZB).

I suspect ZB might be ‘fixing’ the vertex order on re-import, but not correcting
the UV assignment?

I’m going to try messing with an OBJ using a text editor to see if I can figure out
what’s going on.


Just for the record…In case someone else hits this one.

The two polys’s I was having problems with were exported from ZBrush as:

f 5 3 1 7
f 11 9 1 3

After applying UVs and re-exporting from Blender. These two polys, that is, the ‘active’
face and the next (adjacent) poly, were reordered to:

f 1/1 7/2 5/3 3/4
f 1/1 3/4 11/5 9/6

Manually correcting the order to:

f 5/3 3/4 1/1 7/2
f 11/5 9/6 1/1 3/4

Avoids the problem on re-import to ZB, but on a large mesh is probably unworkable.

All other polys (only 206 in this case) are unaffected.

It’s clear Blender is reordering just these two poly’s. I’ve no idea why, but it seems
to be linked to the ‘active face’.

I know the latest ZBrush (3.5R2) can correct some ordering problems on re-import. I
think that’s what’s happening here, but I suspect it’s not correcting the UV’s, which
results in normal poly display in ZB, but flipped textures…