lod generator standalone

[FlankaLanka]

Description

A LOD generator tool. Upload a mesh and create different LOD meshes with QEM algorithm.

https://raw.githack.com/FlankaLanka/three.js/lod-gen/tools/lod-generator/index.html

[mrdoob]

Is QEM the best algorithm? 🤔

[gkjohnson]

I'll just point out that gltf-transform also has a reasonable mesh decimation algorithm (there are a number of easy-to-use tools available for this) so I question whether it's valuable to rewrite it let alone maintain a tool for it in this repo.

[mrdoob]

I'm mostly curious about the algorithm.

If the output could get better we could easily integrate this in the Three.js Editor instead.

[Mugen87]

To clarify, QEM is the approach from Garland and Heckbert [1998] and well know for its conceptual issues like it does not properly preserve uv coordinates such that textures are correctly projected on the simplified meshes.

A very promising approach known from #14058 is this one: https://cragl.cs.gmu.edu/seamless/

In the link you find the related paper, the presentation from SIGGRAPH Asia 2017 and also a GitHub repository with a C++ implementation: https://github.com/songrun/SeamAwareDecimater?tab=readme-ov-file#seam-aware-decimater

[Mugen87]

BTW: Before adding a new component, a PR should improve the existing SimplifyModifier.

https://threejs.org/examples/webgl_modifier_simplifier

[donmccurdy]

I'll just add that the implementation in glTF Transform uses meshoptimizer's 15kb WASM geometry simplifier. The older version of meshoptimizer used in glTF Transform preserves UVs but doesn't optimize for them; the newer version preserves UVs and gives UV error weight during simplification. See donmccurdy/glTF-Transform#1714.

I'd also done a standalone simplification example using meshoptimizer directly in three.js here:

https://discourse.threejs.org/t/mesh-simplification-using-meshoptimizer/63002/4

A nice feature of this approach — specifically for LODs — is that LODs don't need separate vertex attributes, only different indices. Applications could switch between LODs within a geometry using geometry.groups.

[Mugen87]

Closing since the PR in the current state can't be merged.

I'd also done a standalone simplification example using meshoptimizer directly in three.js here:

@donmccurdy I've just tested the approach from your fiddle with our simplifier example and I'm impressed by the result:

https://jsfiddle.net/bpyhv6zj/

Couldn't we ditch the existing implementation of SimplifyModifier and internally use MeshoptSimplifier instead? The code from the fiddle's simplify() function is something we could hide in SimplifyModifier to ease the usage.