Default to trimesh for generated collision shapes in Advanced Import Settings

[Calinou]

This avoids using convex decomposition every time collision is enabled on a mesh, which can be extremely slow on complex meshes (such as entire levels).

This doesn't break compatibility since default values are saved to .import files, unlike .tscn/.tres and project.godot.

We may want to consider though that only StaticBody can use trimesh collision shapes. Other PhysicsBody types can only use convex shapes or primitive shapes, so perhaps we should automatically change the default according to the selected PhysicsBody type. (In this case, simple convex decomposition should be preferred for dynamic objects as it's faster).

• This closes Change default collision shape type in imported 3D scenes away from "convex decomposition" godot-proposals#8059.

[smix8]

Imo what should change is that you can turn on the "generate physics" property without it triggering the calculation. Instead, default it to NONE and let user select what shape they want generated before doing it. Trimesh collision is low quality and low performance so not exactly something that fits a good default.

Just changing the default shape is just adding lipstick on a pig because the real issue is that such a problematic mesh shouldnt be used for collision generation in the first place. If the source mesh is so bad that the convex decomposition takes so long the trimesh will be faster but it will be horrendously low quality and performance broken at runtime, just not in the editor. That is not really doing anyone a favor, it just hides the real issue for some time.

[lyuma]

I think it's good. we should make sure the user does not select Trimesh if the body_type is Dynamic. possibly dynamically changing the default property value in that case.

[akien-mga]

Thanks!

[Malcolmnixon]

This is a breaking change - in that its causing problems loading GLB assets that were configured with SHAPE_TYPE_DECOMPOSE_CONVEX in Godot 4.2 or earlier.

In Godot 4.2 the default shape type was 0 (SHAPE_TYPE_DECOMPOSE_CONVEX), and as such this value wasn't saved in the .import file. When these files are now loaded into Godot 4.3 these GLB files are being given SHAPE_TYPE_TRIMESH colliders.