Tileset with no normals has render and loading issues

[r-veenstra]

I have a tileset used in https://github.com/CesiumGS/cesium-unreal-demos which renders incorrectly in the editor, and also appears to hang the editor on playing the scene (hangs at "reloading domain" and never appears to proceed). It works fine in Unreal.

Using Unity 2022.3 and Cesium for Unity 1.14.0. No errors or warnings appear in the console.

Asset ID: 2887128
Token: Use the existing samples token

I have the same tileset exported with normals, and it appears to work fine.
Working Asset ID: 2887129

[kring]

This is a couple of different bugs.

The first is that the code for populating the vertex color data is incorrect for the case where we don't have normals, and so we have to generate flat normals. This is the cause of the random multicolored triangles. I fixed this here (no PR yet):
2d36729

The second problem is caused by overflowing 16-bit mesh indices. When we generate flat normals, we need to "unshare" the vertices. Every unique triangle gets three of its own unique vertices. This necessarily increases the number of vertices in the mesh. If the number of vertices was originally less than 65535, but the unshared version is more than that, then we'll overflow the uint16_t and get caught in an endless loop. This is the cause of the hang when attempting to enter Play mode.

You can work around both problems by checking the "Generate Smooth Normals" box. But once the tileset is loaded, it's too late (a load thread will be stuck in an endless loop). So you need to load Unity, change the setting, save, exit Unity, kill the hung Unity process, restart it.