This mesh causes "Index was outside the bounds of the array"

[cubrman]

Hi,

In plain english, a non-manifold mesh is one that does not represent a continuous, closed, smooth surface. Common sources of non manifoldness:

- Triangles sharing no edges, but sharing vertices. (there's a couple of these in your shirts sleeves)
- An edge shared by more than 2 triangles. Commonly seen when modelers try to create two-sided cloth by just duplicating every face in the mesh and flipping them, essentially making the entire mesh non-manifold. If you require two-sided meshes you can: use proxies, use a two-sided shader, or use two materials one for each side (this last approach is used in all Obi sample scenes).
- Edges adjacent to 0 faces. (antennae-like edges)
- Rogue vertices (vertices that are part of no edges)
- Adjacent faces with normals pointing in opposite directions (imagine a table whose "top" side abruptly becomes its "bottom" side...not possible in real life, should not happen in 3D models)
- etc.

Border edges (edges shared by only 1 face) are generally regarded as non-manifold, but these are allowed in Obi (not allowed for 3D printing though, which does require perfect non-manifoldness). The meshes included in Obi are all 2-manifold.

I opened the trenchcoat scene and now I know how you reconcile single-sided meshes requirenment with manifold requirenment.

Still, this is what blender shows when selecting non-manifold vertices for the flag mesh that is used in the 'Wind' demo (see image attached).

Why can the flag be allowed while my mesh is not? The edges in my mesh are also only shared with 1 face.