This screenshot shows the problem very well.
I cut off all plygons except the plane which is in the picture.

The plane has two meshes left half, and right half.
I set the same smoothing group to the two meshes of plane.

I randmized the colors for each vertex, and rendered.
Left half is works well. but right half is not.

If I deleted the left half, and render the right half only, It works well.
Why does this inconsistencies occure?

[Edited by - ilys4 on January 31, 2007 2:19:16 PM]

Well, I can't tell exactly from the images. How do they render in 3ds max?
For me it seems like there is some duplication issue. You don't need to write your own exporter, but it would be helpful if you knew how the 3ds-exporter works. Afaik, you can get the source code along with the 3ds max SDK.


To clarify your two questions:

Smoothing groups are masks that are used in 3ds max to define whether a hard or smooth edge should appear between two polygons. If both polygons don't share at least one smoothing group, a hard edge will be visible. The smoothing groups will affect the normal creation and vertex duplication. Afaik, 3ds max duplicates a vertex if two polygons don't share a smoothing group and when calculating the normal for a vertex, only those faces are taken into account that share that particular vertex (not a duplicate).

T-Vertices:

|
0---2---1
0-------1
| |

consider the above illustrated case. The vertices 0 and 1 are only separated for illustration purposes, that means that each of the top polygons share one vertex with the bottom polygon.

When normals are created, every face that uses a vertex is taken into account. For vertex 2 only the upper two faces are used. However for correct lighting, the bottom vertices should be taken into account, too. In normal algorithms this is not done, since the bottom polygon doesn't use vertex 2.