[TRACKER] Automatic mesh LOD issues

[Calinou]

This tracker is about issues related to automatic mesh LOD performed at import-time in 4.0. This feature is not present in 3.x.

See also #70533, which is another common optimization used in 3D rendering.

This tracker does not cover issues related to manual (H)LOD performed using visibility ranges.

Bugs

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1. Vulkan: Vertex colors glitch on 3D model due to automatic mesh LOD #57608
   bug confirmed documentation topic:3d topic:import topic:rendering +6
2. Vulkan: Triangle glitch on a model with a rectangle hole due to automatic mesh LOD #58242
   bug confirmed topic:3d topic:import +4
3. Flat normals can turn smooth in the distance due to automatic mesh LOD #70603
   bug confirmed topic:3d topic:rendering +4
4. MeshInstance3D - Auto LOD Issue #71031
   bug topic:3d topic:import topic:rendering +4
5. Generate Lods option does not import models correctly #71141
   bug confirmed topic:3d topic:animation topic:import +5
6. Meshes drawn incorrectly when too far from camera due to automatic mesh LOD #71567
   bug topic:3d topic:rendering +3
7. Vulkan: Faces on objects with several surfaces disappear under some angles #70759
   bug topic:3d topic:import topic:rendering +4
8. 3D model deforms when playing animations in Godot 4 #72998
   bug topic:import topic:rendering +3
9. [WebGL] - GL_INVALID_OPERATION: Insufficient buffer size due to automatic mesh LOD #74198
   bug platform:web topic:3d topic:rendering +4
10. Godot automatic LOD changing (incorrectly) based on the angle of the camera when using MultiMesh #76436
    documentation topic:3d topic:rendering +3
11. BoneMap retarget on FBX files or FBX2glTF conversions cause broken LODs #76892
    bug topic:3d topic:animation topic:import +4
12. Mesh instantiated from .blend file is shown as broken when viewing from specific angle #77531
    bug topic:3d topic:import +3
13. Vulkan: Importing 3D scene with Static Lightmaps disables automatic LOD #53818
    bug confirmed performance topic:3d topic:rendering +5
14. Vulkan: LOD seems to be flawed, distance seems based on forward basis distance #54885
    bug topic:3d topic:rendering +3
15. Importing Student Art Gallery.glb crashes #57362
    bug confirmed crash topic:3d topic:import +5
16. Vulkan: Automatic mesh LOD always picks lowest level of detail in orthogonal camera #57404
    bug confirmed topic:3d topic:rendering +4
17. Vulkan: Incorrect glTF mesh rendering due to automatic LOD kicking in too early with scaled bones #57895
    bug confirmed regression topic:3d topic:import topic:rendering +6
18. Auto Lod algorithm causes seams between meshes #59024
    bug topic:3d topic:import +3
19. Automatic mesh LOD selection isn't affected by 3D resolution scaling #68484
    bug topic:3d topic:rendering +3
20. Directional Shadow Pancake Size breaks Automatic LOD #78664
    bug topic:3d topic:rendering +3
21. Incorrect display of OpenGL 3 shadows #88123
    bug topic:3d topic:rendering +3
22. LOD system does not recognize when camera enters AABB (solution provided) #88273
    bug topic:3d topic:rendering +3
23. "Generate LODs" can produce lighting bug on imported mesh (glb), camera angle dependent #89394
    bug topic:3d topic:import topic:rendering +4

Enhancements

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1. Generate shadow meshes from a lower LOD level than the source mesh godot-proposals#2600
   topic:3d topic:editor topic:rendering +3
2. Expose properties for setting manually created automatic LOD meshes in the Mesh resource inspector godot-proposals#3860
   topic:3d topic:core +2
3. Improve automatic mesh LOD generation to better preserve silhouettes at high simplification levels godot-proposals#3861
   topic:3d topic:core +2
4. Implement LOD generation when importing OBJ as mesh #65294
   confirmed discussion enhancement topic:3d topic:import +5

[TokisanGames]

How do we generate lods and enable automatic use on already imported meshes? I have hundreds of assets already, stored in Godot's native resource format and saved in text scenes or as text resource files for git.

[Calinou]

How do we generate lods and enable automatic use on already imported meshes? I have hundreds of assets already, stored in Godot's native resource format and saved in text scenes or as text resource files for git.

Automatic LOD generation on import is only supported when importing 3D scenes (glTF/Collada/FBX), not when loading pre-made .mesh/.res meshes or importing 3D meshes (OBJ). That said, you can choose to import OBJ as a 3D scene in the Import dock if you need LOD generation and lightmap UV2 unwrap for OBJ.

There's a generate_lods() method on some class I forgot the name of, but it's more limited and doesn't seem to be meant for public use.

[TokisanGames]

Thanks for the answer, but you're not supporting core features on your own native format (arraymesh)? There are tons of projects right around the corner from migrating to gd4 that won't be able to use lod without manually reimporting a ton. Many of them have meshes stored in scene files as arraymeshes without realizing they are disconnected from their import file.

How do I know? Because the engine pushes you into the native format, because I've continually seen people on my team not realizing they are disconnecting resources from files which get saved in scene files, and because I've seen people do it on github issues.

They're all expecting autolod to just work and apparently it is not going to unless they first discover it's not working, troubleshoot it, write up an issue, then manually reimport every asset, then the setting up all of the auxiliary components again: physicsbodies, collision, materials, layers, parameters, etc.

There is an unusable surfacetool.generate_lod(), but it says Deprecated. Unused internally and neglects to preserve normals or UVs. There is an ImporterMesh.generate_lods(), and the class can output an arraymesh, but I see no way to pass in an arraymesh.

[fire]

In the godot architecture, many procedures are ran on the raw scene before the final output. I was developing the gltf export code but it currently has a duplication nodes bug. I don’t have a good solution to rerunning the import process. Maybe marking as escn?

[fire]

For clarity.

1. Import this glb from https://github.com/KhronosGroup/glTF-Sample-Models/raw/master/2.0/Fox/glTF-Binary/Fox.glb
2. Make local and save as a scn/tscn
3. Go to the filesystem and rename to be .escn
4. It will use the import dialog
5. Noticed that lods are generated.

ESCN Game Project.zip

[TokisanGames]

Thanks for the suggestion. I took one asset, a single MeshInstance, saved it as a tscn, renamed it to escn, brought it back into a scene and saw the import dialog and brought it in w/ Generate LODs. However, no LODs were generated. Moving the camera back and forth, watching w/ Information and Wireframe turned on in the viewport, the mesh and info did not change.

By the way, I probably have 1000 assets. Manually reimporting them one at a time is a very big ask. It's an unreasonable process considering:

• LOD generation is already in the engine
• The process above suggests a way to use LOD Generation on already imported assets is already or mostly implemented, so should continue towards full support
• The native format (arraymesh) should be treated as a first class citizen for reasons given in my last comment above.

[fire]

I would try to get escn to operate on mesh instances instead of the importer mesh instance. It's a bug.

The other proposals don't have any plumbing in place, so it would be some work

#63498

[TokisanGames]

Thanks I'll follow the issue. If you want to get LOD generation to work on a meshinstance, rather than arraymesh, then workflow-wise, it would be reasonable to right-click the mesh instance and select Generate Lods. Or left-click the MeshInstance, click the Mesh menu, and Generate LODs. That should be the same as saving as escn and reopening, but would save developers a lot of clicks and manual work. Doing it once isn't a big deal, but it adds up if you have to do it hundreds of times.

[fire]

Does anyone know which issue describe lod generation being slow?

Profiles suggest https://share.firefox.dev/3ZY1DSC that:

1. SurfaceTool::generate_tangents takes 73% of the total runtime