Mesh.bindposes

Description

The bind poses. The bind pose at each index refers to the bone with the same index.

Each matrix in bindposes is the inverse of the transformation matrix of the bone, calculated when the bone is in its base state (its bind pose).

Note: See the Mesh page where example 2 shows vertices being copied, updated and and re-assigned to the Mesh. The example on this page also updates bindposes, SkinnedMeshRenderer.bones and SkinnedMeshRenderer.sharedMesh in the same way.

using System.Collections.Generic;
using UnityEngine;

public class RestoreBindposeUtility : MonoBehaviour
{
    [ContextMenu("Restore Bindpose")]
    void RestoreBindpose()
    {
        // Get the SkinnedMeshRenderer component from this GameObject.
        var renderer = GetComponent<SkinnedMeshRenderer>();
        // Create a dictionary to map each bone transform to its bindpose matrix for quick lookups.
        var bindposes = new Dictionary<Transform, Matrix4x4>();

        // Populate the dictionary by iterating through the bones and their corresponding bindposes.
        for (int i = 0; i < renderer.bones.Length; ++i)
            bindposes.Add(renderer.bones[i], renderer.sharedMesh.bindposes[i]);

        // Iterate over each bone to reset its transform to its original bind pose.
        foreach (var bone in renderer.bones)
        {
            // Get the bone's bindpose matrix, which transforms from the bone's local space to world space.
            var matrix = bindposes[bone];
            // Get the inverse of the bindpose matrix, which transforms from world space to the bone's local space.
            var wMatrix = matrix.inverse;

            // Check if the current bone is a root bone of the rig by seeing if its parent is not in the dictionary.
            var isRootBone = !bindposes.ContainsKey(bone.parent);
            // If the bone is not a root bone, calculate its local transformation relative to its parent.
            if (!isRootBone)
            {
                if (bone.parent)
                    // To get the local matrix, multiply the bone's bindpose by the inverse of its parent's bindpose.
                    // This cancels out the parent's transformation, leaving the local transformation.
                    matrix *= bindposes[bone.parent].inverse;

                // Invert the resulting matrix to get the final local-to-parent transformation.
                matrix = matrix.inverse;

                // Decompose the local matrix to extract and set the bone's local scale and position.
                bone.localScale = new Vector3(
                    matrix.GetColumn(0).magnitude,
                    matrix.GetColumn(1).magnitude,
                    matrix.GetColumn(2).magnitude
                    );
                bone.localPosition = matrix.MultiplyPoint(Vector3.zero);
            }
            // Set the bone's world rotation from the inverse bindpose matrix.
            bone.rotation = wMatrix.rotation;
        }
    }
}