Is it possible to create a box CollisionShape3D that automatically matches the bounds of a MeshInstance?

[wulfara]

Godot Version

4.3

Question

I want to add some walls and obstacles the simplest collision shape possible (a box) and I was wondering if there is a way to automatically add from the editor a CollisionShape3D that matches the size and bounds of a mesh instance. Just like you can use the menu “Mesh → Create collision shape…” for adding more complex collisions (trimesh, single convex…) but lacks this more simple box approach.

I just want to automatically create box collision shapes that matches exactly that orange cube that the editor is drawing around the model.

Thank you in advance.

[Locher]

Let’s say you have an MeshInstance3d called object that has its own mesh called objectMesh applied:

	var collision_shape = CollisionShape3D.new()
	collision_shape.shape = objectMesh.create_trimesh_shape()
	var static_body = StaticBody3D.new()
	static_body.add_child(collision_shape)
	object.add_child(static_body)

I am not sure if this will work or will lead to solve your situation, I only have experience with array meshes.

Our approach is to create a new CollisionShape3D object with its shape formed by our mesh input. Then we add this CollisionShape3D to an appropriate node that can make use of it (like a StaticBody3D) which we will then add to the MeshInstance3D object.

The Object Tree looks like this:

• MeshInstance3D root-node + mesh
  • StaticBody3D
    • CollisionShape3D has collision data based on the mesh

[wulfara]

@Locher

var collision_shape = CollisionShape3D.new()
	collision_shape.shape = objectMesh.create_trimesh_shape()
	var static_body = StaticBody3D.new()
	static_body.add_child(collision_shape)
	object.add_child(static_body)

Hi! Thank you for your answer.

But the method you described adds a trimesh shape with the shape of the mesh (just like the menu “Mesh → Create Collishion Shape…”). What I’m trying to achieve is to create a box collision shape with the dimensions and positioning of the mesh.

Greetings.

[Locher]

Then I believe you can just create a BoxShape3D and set the shape as you need?

BoxShape3D

It might be even easier because as a Box, you only need to set x, y and z.

[wulfara]

Well I have created a function that does exactly what I want. It looks like this:

@export var mesh_instance : MeshInstance3D

func create_box_collision_shape():
	if not mesh_instance: return
	if not mesh_instance.mesh: return
	
	var box_collider = CollisionShape3D.new()
	box_collider.shape = BoxShape3D.new()
		
	var aabb = mesh_instance.get_aabb()
	box_collider.shape.size = aabb.size
	box_collider.position = aabb.position + aabb.size / 2

	add_child(box_collider)
	box_collider.owner = self

I was going to post a proposal for adding this to the Mesh “Add Collision Shape” context menu for convenience but I have found that there is already a proposal for it here.