Hi PaQ, yeah, it is related to the centroid triangulation method, in combination with a low number of polygons being generated.

That centroid triangulation method can be disabled in the moi.ini file under:

[Mesh Export]
CentroidTriangulation=n


However, if you have enough polygons being generated (so that there aren't areas with a sudden shift from one polygon to the next), and your renderer is using the good vertex normals, then the artifact will go away even if centroid triangulation is enabled.


The centroid triangulation method means to convert an n-gon into triangles when possible by connecting all the n-gon's outline points to a center averaged point.

In a lot of circumstances it actually makes for a nicer triangulation, here's an example, meshing this face:



With the centroid triangulation method, a centroid point is added and the points from the outside all connect to it, making a nicely symmetrical and radial type triangle arrangement:




Compare that to the non-centroid triangulation method here, where no internal points are added and instead triangles are only connected up between the existing points of the n-gon:




However, there are some cases where adding in the centroid point causes problems.


The centroid point gets its own vertex normal, and if you have a kind of long and skinny n-gon it's possible for the centroid point to have a fairly different shading applied to it than to the outer points, that's what creates the kind of shading problem that was originally shown in this thread. It can be especially noticeable if some neighboring n-gon was actually a quad and so did not get any centroid added to it, so it only has shading vertex normals at the far points of the quad.


The other kind of thing that can be bad when trying to generate a low polygon output is if the centroid point pops out a fair distance from the other points (because the centroid point is actually evaluated to hug the true surface, it's not actually just a direct average of the other points.


I can probably make some refinements to the centroid triangulation in the future to disable it some of these situations where it is not so good, like maybe not do it on n-gons that have a wide aspect ratio.

But if you have used some other settings like "Divide larger than" to avoid too rough of polygons it won't be a problem.


The centroid point issue is also moot if you export using n-gons which for the original poster of this thread would be recommended since they are going into Cinema4D.

- Michael