Add a mesh simplification option for TriMesh collision shape generation in the advanced import settings

[Calinou]

Describe the project you are working on

The Godot editor 🙂

Describe the problem or limitation you are having in your project

Levels with complex geometry will have complex triangle meshes generated by default, which lowers physics simulation performance and reliability. Maximizing physics server performance is important for games where CPU cycles come at a premium (mobile/web platforms) and for game servers that use server-side physics.

Using a separate hand-authored collision mesh with less details will result in faster and more reliable collisions. However, while iterating on the level geometry, having to maintain this mesh separately can take a lot of time.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Add an option to simplify the generated trimesh collision shape using a decimation algorithm (below Shape Type when Trimesh is selected):

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

Like for LOD generation, use meshoptimizer to create a less detailed version of the base mesh to use as triangle data for a concave CollisionShape. By default, I would recommend using a very low level of simplification to weld faces that have no concrete angle difference. In meshoptimizer, this can be done by using a simplification threshold of 0.0001.

Unlike for occluder generation, we probably don't have to worry about shrinking the generated collider along the normal or something along those lines.

I created a minimal project for testing the feature implementation (4.0 only): test_trimesh_collision_simplify.zip

I have a WIP branch with an implementation of this feature, but I don't know if I'll be able to complete it: https://github.com/Calinou/godot/tree/trimesh-generation-add-simplification

If this enhancement will not be used often, can it be worked around with a few lines of script?

This may be feasible with a custom import script, but it will require more than a few lines of code.

Is there a reason why this should be core and not an add-on in the asset library?

This is about improving performance in situations where creating hand-made shapes is not feasible due to lack of time or resources.