Updating bone rests in a Skeleton3D via code does not update the global rest as well

[alexnikop]

Tested versions

• Reproducible in 4.4.0
• Not reproducible in 4.3.0

System information

Windows 11 Godot Engine v4.4.stable.mono.official.4c311cbee Vulkan 1.3.289 - Forward+ - Using Device #0: NVIDIA - NVIDIA GeForce RTX 4070 SUPER

Issue description

Adding bones to a Skeleton3D via code does not update the global rest transform as well.

Steps to reproduce

1. Create A Skeleton3D Node
2. Add bones to the skeleton via code in a chain-like fashion (Every next bone is child of the previous one)
3. Update the bone rests using set_bone_rest function
4. Print global rests of all bones using get_bone_global_rest and see that global rests do not change

Minimal reproduction project (MRP)

extends Skeleton3D

func _ready() -> void:
	
	# number of bones to spawn
	var num_bones: int = 4
	
	# create sample transform 3D
	var transform: Transform3D = Transform3D.IDENTITY
	transform.origin = Vector3(0, 1, 0)
	
	for b in num_bones:
		# add bone in skeleton
		add_bone(str(b))
		# set bone rest
		set_bone_rest(b, transform)
		
		# set previous bone as parent bone
		if b > 0:
			set_bone_parent(b, b-1)
		
		# print bone rest and global rest
		print("**************")
		print(get_bone_rest(b))
		print(get_bone_global_rest(b))

This code above prints the following results:

**************
[X: (1.0, 0.0, 0.0), Y: (0.0, 1.0, 0.0), Z: (0.0, 0.0, 1.0), O: (0.0, 1.0, 0.0)]
[X: (1.0, 0.0, 0.0), Y: (0.0, 1.0, 0.0), Z: (0.0, 0.0, 1.0), O: (0.0, 0.0, 0.0)]
**************
[X: (1.0, 0.0, 0.0), Y: (0.0, 1.0, 0.0), Z: (0.0, 0.0, 1.0), O: (0.0, 1.0, 0.0)]
[X: (1.0, 0.0, 0.0), Y: (0.0, 1.0, 0.0), Z: (0.0, 0.0, 1.0), O: (0.0, 0.0, 0.0)]
**************
[X: (1.0, 0.0, 0.0), Y: (0.0, 1.0, 0.0), Z: (0.0, 0.0, 1.0), O: (0.0, 1.0, 0.0)]
[X: (1.0, 0.0, 0.0), Y: (0.0, 1.0, 0.0), Z: (0.0, 0.0, 1.0), O: (0.0, 0.0, 0.0)]
**************
[X: (1.0, 0.0, 0.0), Y: (0.0, 1.0, 0.0), Z: (0.0, 0.0, 1.0), O: (0.0, 1.0, 0.0)]
[X: (1.0, 0.0, 0.0), Y: (0.0, 1.0, 0.0), Z: (0.0, 0.0, 1.0), O: (0.0, 0.0, 0.0)]

The second line in every segment is the global bone rest. As you can see the origin of the transforms does not update

[Alex2782]

Tested and reproduced.

blame Skeleton3D::set_bone_parent

maybe PR: #97744

[Drac32Drac]

I just spent the past few days struggling with this one. I can confirm that this bug exists in 4.4.0

Is there a workaround to this? Or alternatively a way to simply apply the entire current pose to the rest pose?
The editor button that applies the entire current pose to the rest pose seems to work. But that function as best I can tell isn't accessible from code.

[alexnikop]

As a workaround I calculate the global rest myself every time I create a new bone and save it in a dictionary. After that I can just retrieve any global rest from the dictionary when needed. Here is the relevant code to help you build a temporary solution until the issue is fixed.

Dictionary<int, Transform3D> boneGlobalRests;

public void SetSkeletonBoneGlobalRest(int boneIdx, Transform3D rest)
{
	int parentIdx = Skeleton.GetBoneParent(boneIdx);
	if (parentIdx == -1)
	{
		boneGlobalRests.Add(boneIdx, rest);
	}
	else
	{
		boneGlobalRests.Add(boneIdx, boneGlobalRests[parentIdx] * rest);
	}
}

Feel free to ask any more help on how to work around this

[Drac32Drac]

I found another workaround that seems to work just fine.

Calculate and apply the LOCAL bone rests BEFORE parenting it to another bone and it updates the rests properly.