How do you copy bone rotation in Unity?

How to Copy Bone Rotation in Unity?

In Unity, you can efficiently copy bone rotation from one bone to another directly within the editor by utilizing the Transform component's properties. This manual method allows for precise transfer of rotational data between game objects representing bones.

Manually Copying Bone Rotation in Unity

The most straightforward way to copy bone rotation involves using Unity's Inspector window to copy and paste the Transform component's rotation values. This is particularly useful for character rigging adjustments, pose mirroring, or transferring specific orientations between similar bone structures.

Step-by-Step Guide

Follow these steps to copy and paste bone rotation:

Locate the Bone Structure:
- Open your Unity project and navigate to the Hierarchy window.
- Find the GameObject representing your character model or skeletal rig.
- Expand the hierarchy to reveal the individual GameObjects that act as bones (e.g., Hips, Spine, UpperArm, LowerArm, Hand).
Select the Source Bone:
- In the Hierarchy window, select the source bone – the GameObject whose rotation you wish to copy.
Copy Rotation Values:
- With the source bone selected, observe its Transform component in the Inspector window.
- Locate the Rotation property within the Transform component.
- Right-click directly on the "Rotation" label itself.
- From the context menu that appears, select Copy Property (or Copy Value, depending on Unity version and context) to copy the entire rotation vector (X, Y, Z, and W for Quaternions internally).
- Alternatively, you can manually select and copy the individual X, Y, Z values if viewing in Euler angles.
Select the Target Bone:
- In the Hierarchy window, select the target bone – the GameObject where you want to apply the copied rotation.
Paste Rotation Values:
- With the target bone selected, go to its Transform component in the Inspector window.
- Locate the Rotation property.
- Right-click on the "Rotation" label.
- From the context menu, select Paste Property (or Paste Value). This action will replace the target bone's current rotation with the copied values from the source bone.

For more information on the Transform component, refer to the official Unity Transform documentation.

Important Considerations

When copying bone rotation, keep the following in mind:

Local vs. World Rotation: The values displayed and copied in the Inspector typically represent the local rotation of the bone relative to its parent. Copying these values is generally what you want for transferring bone poses. If you need to match world space rotation, you might need to adjust for parent rotations or use scripting.
Parent Hierarchy: Even with identical local rotations, bones in different parent hierarchies or with different parent rotations will have different world orientations. Ensure your target bone's parent structure is appropriate for the desired result.
Animation Overrides: If the bone is part of an animated character, any copied rotation might be overridden by the animation system during play mode unless you specifically disable animation for that bone or update its rotation via a script after animation has applied.

Programmatic Bone Rotation Copying

For scenarios requiring dynamic or runtime bone rotation transfer, especially in complex character setups or procedural animations, scripting offers a robust solution:

C# Scripting: You can access the transform.rotation (world rotation) or transform.localRotation (local rotation) property of a source bone and assign it to the corresponding property of a target bone within a C# script. This is often done in LateUpdate() to ensure it applies after animation updates.

// Example C# code snippet
public Transform sourceBone;
public Transform targetBone;

void LateUpdate()
{
    if (sourceBone != null && targetBone != null)
    {
        // Copy local rotation
        targetBone.localRotation = sourceBone.localRotation;

        // Or copy world rotation (less common for individual bone adjustments)
        // targetBone.rotation = sourceBone.rotation;
    }
}

Animation Tools: For more advanced animation retargeting or mirroring, Unity's built-in Humanoid Rig Setup and various third-party animation tools provide dedicated features to copy, mirror, and remap bone rotations across different characters or rigs.