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

[josemendez]

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.

Blender shows border edges as non-manifold because strictly speaking, a non-watertight closed mesh is non-manifold. However as I previously mentioned, Obi relaxes the definition of non-manifoldness and allows border edges.

However in the case of your shirt, there's non-manifold geometry other than border edges. For instance, this vertex is shared by two faces that do not share any edge:



A possible fix would be welding the two vertices at its left, so that the faces now share an edge.