MeshDataTool showing no vertices after create_from_surface

[mboll]

Godot Version

v4.4.1

Question

I’d like to work with the vertices and faces of an existing BoxMesh, so I’m using MeshDataTool. I read in the mesh with MeshDataTool.create_from_mesh, but after doing so, the MDT says it does not have any vertices. I’ve read through the tutorial and related documentation as much as I can, but I can’t see where I’m going wrong.

Example

Here’s a reproducible example. Create a new scene with Node3D as the root, add a MeshInstance3D, and to that mesh instance add a BoxMesh. Attach the following script to the root node:

extends Node3D

@onready var mesh_in = $MeshInstance3D

func _ready() -> void:
	var mesh: Mesh = mesh_in.mesh
	print(mesh.get_surface_count())  # prints 1
	print(len(mesh.get_faces()))  # prints 36
	
	var mdt = MeshDataTool.new()
	mdt.create_from_surface(mesh, 0)
	print(mdt.get_vertex_count())  # prints 0

Here’s a screenshot of the setup (with terminal output) and the script.

Am I missing something obvious? Or something not obvious? The faces of BoxMesh are tris, right? Thanks in advance.

[mrcdk]

MeshDataTool.create_from_surface() expects an ArrayMesh. A BoxMesh is not an ArrayMesh it extends PrimitiveMesh You’ll probably need to use PrimitiveMesh.get_mesh_arrays() to generate the ArrayMesh (like the snippet in the documentation shows) before using it in the MeshDataTool

[mboll]

You’re right, that was the issue after all. I hadn’t seen the type that create_from_surface wanted, just assumed it was any Mesh.

I added an intermediate step to convert any Mesh to an ArrayMesh. The result from this can then be read with MeshDataTool.create_from_mesh. Not sure if this is necessary for base meshes, but it certainly works for PrimitiveMesh.

func convert_to_array_mesh(mesh: Mesh) -> ArrayMesh:
	var surface_array = mesh.surface_get_arrays(0)
	var array_mesh := ArrayMesh.new()
	array_mesh.add_surface_from_arrays(Mesh.PRIMITIVE_TRIANGLES, surface_array)
	return array_mesh

Thanks for your reply!