I have been seeing this issue for a long while.
Observation: Certain triangles that can be described as long, two long sides + one short, with vertex distances at some distance apart/angle will not be processed on mesh import.
Original Mesh (section from a larger mesh I isolated):
- Attempts to fix:
- Rebuilt mesh from scratch
- Exported FBX from maya
- Exported OBJ from maya
- Exported FBX from 3ds Max
- Exported FBX from Blender
- Unchecked remove degenerate triangles
on import (even though this is not
degenerate)
Ways to get the geometry to process (though these are unacceptable)
- Move the verticies so that the triangle angles are not so steep (change geometry in a way that I do not want)
- Insert an edge loop which also shortens the long-triangle (adding geometry I do not want)
Here is an example (insert edge loop):
Conclusion: If I build a mesh I want all triangles to import. The issue appears isolated to the mesh import process in Unreal 4. I have imported the same mesh into UDK (unreal 3) without issues, as well as Unity 3D game engine, no issues.
I do not want to alter my mesh to make the issue go away, that is unacceptable. If I painted a whole terrain or cave area with vertex colors, then realized there was an issue hours after working, I run the risk of re-doing my work after ‘fixing’ this missing triangle.
THIS IS NOT a reversed normal or missing triangle. Download FBX for yourself.
FBX: https://drive.google.com/file/d/0B9NKCA33MwbjQ2xMWFZ1Qzd6OEE/view?usp=sharing