Mesh.bindposes

Description

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

The bind pose is the inverse of the transformation matrix of the bone, when the bone is in the bind pose.

using UnityEngine;
using System.Collections;

// this example creates a quad mesh from scratch, creates bones
// and assigns them, and animates the bones motion to make the
// quad animate based on a simple animation curve.
public class BindPoseExample : MonoBehaviour
{
    void Start()
    {
        gameObject.AddComponent<Animation>();
        gameObject.AddComponent<SkinnedMeshRenderer>();
        SkinnedMeshRenderer rend = GetComponent<SkinnedMeshRenderer>();
        Animation anim = GetComponent<Animation>();

        // Build basic mesh
        Mesh mesh = new Mesh();
        mesh.vertices = new Vector3[] { new Vector3(-1, 0, 0), new Vector3(1, 0, 0), new Vector3(-1, 5, 0), new Vector3(1, 5, 0) };
        mesh.uv = new Vector2[] { new Vector2(0, 0), new Vector2(1, 0), new Vector2(0, 1), new Vector2(1, 1) };
        mesh.triangles = new int[] { 0, 1, 2, 1, 3, 2 };
        mesh.RecalculateNormals();
        rend.material = new Material(Shader.Find("Diffuse"));

        // assign bone weights to mesh
        BoneWeight[] weights = new BoneWeight[4];
        weights[0].boneIndex0 = 0;
        weights[0].weight0 = 1;
        weights[1].boneIndex0 = 0;
        weights[1].weight0 = 1;
        weights[2].boneIndex0 = 1;
        weights[2].weight0 = 1;
        weights[3].boneIndex0 = 1;
        weights[3].weight0 = 1;
        mesh.boneWeights = weights;

        // Create Bone Transforms and Bind poses
        // One bone at the bottom and one at the top

        Transform[] bones = new Transform[2];
        Matrix4x4[] bindPoses = new Matrix4x4[2];
        bones[0] = new GameObject("Lower").transform;
        bones[0].parent = transform;
        // Set the position relative to the parent
        bones[0].localRotation = Quaternion.identity;
        bones[0].localPosition = Vector3.zero;
        // The bind pose is bone's inverse transformation matrix
        // In this case the matrix we also make this matrix relative to the root
        // So that we can move the root game object around freely
        bindPoses[0] = bones[0].worldToLocalMatrix * transform.localToWorldMatrix;

        bones[1] = new GameObject("Upper").transform;
        bones[1].parent = transform;
        // Set the position relative to the parent
        bones[1].localRotation = Quaternion.identity;
        bones[1].localPosition = new Vector3(0, 5, 0);
        // The bind pose is bone's inverse transformation matrix
        // In this case the matrix we also make this matrix relative to the root
        // So that we can move the root game object around freely
        bindPoses[1] = bones[1].worldToLocalMatrix * transform.localToWorldMatrix;

        // bindPoses was created earlier and was updated with the required matrix.
        // The bindPoses array will now be assigned to the bindposes in the Mesh.
        mesh.bindposes = bindPoses;

        // Assign bones and bind poses
        rend.bones = bones;
        rend.sharedMesh = mesh;

        // Assign a simple waving animation to the bottom bone
        AnimationCurve curve = new AnimationCurve();
        curve.keys = new Keyframe[] { new Keyframe(0, 0, 0, 0), new Keyframe(1, 3, 0, 0), new Keyframe(2, 0.0F, 0, 0) };

        // Create the clip with the curve
        AnimationClip clip = new AnimationClip();
        clip.SetCurve("Lower", typeof(Transform), "m_LocalPosition.z", curve);
        clip.legacy = true;

        // Add and play the clip
        clip.wrapMode = WrapMode.Loop;
        anim.AddClip(clip, "test");
        anim.Play("test");
    }
}

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.