Limit mesh complexity in LOD generation to prevent crashing

[aaronfranke]

This PR fixes the crash in #80431. Instead of crashing, Godot will now print this message:

WARNING: Mesh LOD generation failed for mesh grass_Plane_009 surface 0, mesh is too complex. Some automatic LODs were not generated.
     at: generate_lods (scene/resources/importer_mesh.cpp:479)

I set the limit to 5000000 (5 million). I'm not certain what the limit should be, but a limit of 6 million crashes.

Note: I suspect that there is a bug in the LOD generator and that the limit should be higher than this. However, even if the limit should be higher, it's still good to have some kind of limit that prints a meaningful message instead of crashing. Also, this mesh lags Godot, so LODs are not the only problem with a mesh this big.

[Saul2022]

I guess for such kind of meshes the better could be mesh streaming as it designed for that.

[lyuma]

I'm confused: The check is happening after the LOD was generated. If new_index_count > 5000000 then that means it was successful.

Shouldn't this be checking the index count before calling into SurfaceTool?

[clayjohn]

I am also a little worried that this crash is VRAM amount dependent. The limit is likely different depending on your hardware

[Calinou]

I am also a little worried that this crash is VRAM amount dependent. The limit is likely different depending on your hardware

The GPU used in #80431 has 8 GB of VRAM, so this will affect most users in this case. Even if you happen to have a GPU with more than 8 GB of VRAM, it's not guaranteed that everyone working on your project will also have a GPU with more than 8 GB of VRAM.

[fire]

What feedback is required? Do we need to send 6 million triangle scenes and see what happens?

[aaronfranke]

I don't know what people prefer as the optimal solution, but not crashing is better than crashing.

So if it's up to me, I would merge this to fix the immediate issue, and it can be improved later.

[adamscott]

Reviewed during #animation / #asset-pipeline meeting. This is a workaround/hack to "fix" the issue until we actually find the issue. Only happens when you have a single mesh of ~200Mb.

[akien-mga]

Thanks!

[YuriSizov]

Cherry-picked for 4.1.3.