Skeleton3D Bone indices not identical to those in mesh surface/ arrays?

whoozzem · January 18, 2026, 12:10pm

Godot Version

4.5

Question

Edit:

I believe this may actually be a bug, so I’ve now submitted it to github:

github.com/godotengine/godot

Mismatch Bone Indices between Surface Arrays and Skeleton3D Bone Hierarchy

opened 12:57PM - 19 Jan 26 UTC

chiefwhosm

discussion topic:animation topic:3d

### Tested versions 4.5.1 ### System information Debian 13 ### Issue descrip…tion I have a Skeleton3D with the following bone heierarchy: hips>spine>chest>chest1>neck>head>jaw Using scripting, Godot returns the above names as being these indices in the Skeleton3D: 0 > 1 > 2 > 3 > 4 > 5 > 6 > 7 > 8 I have tried both using the surface_get_arrays command and the MeshDataTool to read the vertices, bones and weights from the mesh assigned to the Skeleton3D - all methods produced identical output arrays. In the array of vertices, the position of vertex 0 on my test rigged character is in the head, approximately at the left eye socket. Vertex 0 should therefore return its bones/weights as being the head bone. However, this is not the case, the bones indices do not match the original Skeleton3D, as shown in my output below: (-2.833333, 148.9722, 12.62367) // Vertex 0's position (at the left eye socket on test character). 26 //Bone Index f_index.02.L //Bone name for this bone index - in this case the 2nd index finger 0.9219958782196 //Bone Weight for this bone 19 upper_arm.L 0.07798886299133 0 hips 0.0 0 hips 0.0 This makes it look as if the surface arrays use a different bone index compared to the original Skeleton3D. ### Steps to reproduce Create a scene containing: 1) A root Node3D 2) A Skeleton3D with bound MeshInstance3D (attached to the root Node3D). 3) A MeshInstance3D with a box mesh, scaled to be fairly small (0.02) and attached to the Skeleton3D. Attach the following code in a script to the Skeleton3D's MeshInstance3D. Use the code to get the surface information for Vertex 0, and position the box mesh to the vertex location in local space: ``` @tool extends MeshInstance3D func _ready() -> void: var mdt = MeshDataTool.new() mdt.create_from_surface(mesh, 0) #Simple cube mesh to move round the vert positions to check where the array thinks a vertex is. # You may need to change the child value to get the box in your scene. var box : MeshInstance3D = get_parent().get_child(2); #Start the cube at the position of the MeshInstance3D we're using for testing. box.position = self.position; #Get Vertex0's bones and weights arrays. var vert0bones = mdt.get_vertex_bones(0) var vert0weights = mdt.get_vertex_weights(0) #Move the cube to our vertex0 position so we can see where this is in 3D space. box.position = mdt.get_vertex(0) #Print the vertex 0 position and for each bone print its weight, associated name and weight value. print (mdt.get_vertex(0)) for i in vert0bones.size(): print(vert0bones.get(i)) print(get_parent().get_bone_name(vert0bones.get(i))) print (vert0weights.get(i)) ``` View the output and confirm against your Skeleton3D hierarchy that the bone index/name output is right/wrong for that vertex position. ### Minimal reproduction project (MRP) N/A