Bone Follower component "Z position" does not account for Z offset

zepht

Problem statement

Due to the context of my project, I am running a spine skeleton rig with an opaque shader, therefore I have added Z spacing to my rig to prevent z-fighting. The character in my project wears a necklace with a bone to which a pendant is supposed to be slotted into, therefore I have created an object with a bone follower to attach a visual to the pendant.

This can work as intended with following the intended bone on XY and rotation, but doesnt work for when the player turns around, which has the bone behind the torso, but the pendant does not care and renders in front anyways. This is not a rendering issue, for the pendant can be obscured by the body, but rather an issue because the Z depth of the pendant is not affected by the depth of the associated bone.

My diagnosis arises with the fact that despite "Follow Z Position" being checked on the BoneFollower, it ignores the Z position created by the "Z Spacing" on the SkeletonAnimator.

The Z spacing has been exaggerated in the screenshots for demonstration purposes

Intended:
Facing Forwards: (note how the selected object should be sandwiched between the head and necklace layers)
{Intended Forwards}

Facing Backwards:
{Intended Back}

Resultant:
Facing Forwards: (notice how the depth coordinate remains entirely unchanged)
{Result Forwards}

Facing Backwards:
{Result Back}

Editor information

Spine Unity 4.2 - Just updated trying to fix this issue
Unity 6000.0.32f1

Spinebot

The issue you're experiencing with the BoneFollower component not accounting for Z offset is due to the fact that the "Follow Z Position" option in the BoneFollower does not consider the Z spacing set in the SkeletonAnimator. This is a known limitation, as the Z position in Spine is primarily used for draw order rather than actual 3D positioning. To address this, you might need to manually adjust the Z position of the pendant object in your Unity scene to match the intended Z offset of the bone it follows. Alternatively, you could modify the BoneFollower script to account for the Z spacing by adding the Z offset to the bone's position.

zepht

I have modified the relevant scripts and implemented the functionality myself. The case has been resolved.

In BoneFollower I made such adjustment

		} else { // For special cases: Use transform world properties if transform relationship is complicated
			if (!skeletonTransform) return;

			Vector3 targetWorldPosition = skeletonTransform.TransformPoint(new Vector3(bone.WorldX, bone.WorldY, SkeletonRenderer.GetBoneDepth(bone) )); // Added "SkeletonRenderer.GetBoneDepth(bone)" replacing "0f"
			if (!followZPosition) targetWorldPosition.z = thisTransform.position.z;
			if (!followXYPosition) {
				targetWorldPosition.x = thisTransform.position.x;
				targetWorldPosition.y = thisTransform.position.y;
			}

And at the end of SkeletonRenderer I simply added the function

	public float GetBoneDepth(Bone bone)
	{
		return zSpacing * skeleton.DrawOrder.FindIndex( x => x.Bone == bone);
	}

Harald

Glad to hear you've found a solution, thanks for letting us know!

Note that you actually don't need to modify SkeletonRenderer but could instead access skeletonRenderer.zSpacing from BoneFollower or your own custom BoneFollower subclass. This way you don't have to modify the runtime.

Harald

@zepht We have added an official parameter to the BoneFollower components. From the changelog:

Added option to BoneFollower components to follow attachment Z spacing offset. The Inspector component property can be found under Follow Z Position - Attachment Z Spacing. Defaults to false to maintain existing behaviour.

A new spine-unity 4.2 unitypackage is available for download:
https://esotericsoftware.com/spine-unity-download
Please let us know if this resolves the issue on your end as well. Thanks for reporting.