【动画】unity中实现骨骼蒙皮动画

news2025/6/5 19:00:33

我是一名资深的游戏客户端，没事的时候我就想手搓轮子

本文目标

搓一个骨骼动画的核心实现，促进理解骨骼动画本质

骨骼动画简介

官方解释上网搜或者问豆包

快速理解

想知道骨骼动画怎么个事要先知道模型是怎么个事
简单来说：模型 = 顶点数据 + 三角形 + 材质
骨骼动画 = 模型 + 骨骼权重数据
骨骼权重数据是编辑器下由美术编辑出来的数据，指明某个顶点受到几根骨骼影响，每个骨骼权重是什么
在unity里，骨骼就是transform

思路

在unity里自己实现一个组件，自己做骨骼对顶点的影响，完成蒙皮
骨骼的transform驱动还靠unity的Animation，在自己的组件里获取骨骼transform就够了
参照SkinnedMeshRenderer设计自己的组件
骨骼动画核心公式，求顶点位置：skinnedVertex = 加权求和(骨骼local2world矩阵 * 顶点初始位置矩阵 * vertex * weight)
只要能拿到顶点，骨骼transform，顶点初始位置矩阵，权重数据，就可以求出来模型某个顶点在动画中某一帧的位置

准备数据

模型，fbx模型文件的mesh
获取骨骼

深度遍历根骨骼的子节点是不行的，里面有用不上的transform不是骨骼，得解析fbx模型文件
FBX模型文件里有骨骼数据形如：Deformer: "SubDeformer::Cluster DummyMesh B-hips", "Cluster"
解析fbx费事，不是核心代码，用SkinnedMeshRenderer的接口bones获取

权重数据，用Mesh的boneWeights接口，一个顶点最多受到4个骨骼影响，基本够用
顶点初始位置矩阵，用Mesh的bindposes接口获得

开搓

using UnityEngine;

namespace HotPlayer.Demos
{
    [ExecuteInEditMode]
    public class HotSkinnedMeshRenderer : MonoBehaviour
    {
        public Mesh mesh;

        public Material material;

        public bool castShadow = true;

        public bool receiveShadow = true;

        public bool useLightProbes = true;

        private Mesh skinnedMesh;

        private Vector3[] vertices;

        private BoneWeight[] boneWeights;

        private Transform[] bones;

        void Start()
        {
            skinnedMesh = Instantiate(mesh);
            skinnedMesh.name = mesh.name + "_Skinned";
            boneWeights = skinnedMesh.boneWeights;
            vertices = skinnedMesh.vertices;
            bones = gameObject.GetComponent<SkinnedMeshRenderer>().bones;
        }

        private void OnDestroy()
        {
            if (skinnedMesh != null)
            {
                if (Application.isPlaying)
                {
                    Destroy(skinnedMesh);
                }
                else
                {
                    DestroyImmediate(skinnedMesh);
                }
            }
        }

        private void UpdateVertices()
        {

            for (var i = 0; i < boneWeights.Length; i++)
            {
                BoneWeight boneWeight = boneWeights[i];
                Vector3 vertex = mesh.vertices[i];

                Vector3 skinnedVertex = Vector3.zero;
                var index = boneWeight.boneIndex0;
                Transform bone;
                if (index > 0)
                {
                    bone = bones[index];
                    var boneMatrix = bone.localToWorldMatrix * mesh.bindposes[index];
                    skinnedVertex += boneMatrix.MultiplyPoint3x4(vertex) * boneWeight.weight0;
                }
                index = boneWeight.boneIndex1;
                if (index > 0)
                {
                    bone = bones[index];
                    var boneMatrix = bone.localToWorldMatrix * mesh.bindposes[index];
                    skinnedVertex += boneMatrix.MultiplyPoint3x4(vertex) * boneWeight.weight1;
                }
                index = boneWeight.boneIndex2;
                if (index > 0)
                {
                    bone = bones[index];
                    var boneMatrix = bone.localToWorldMatrix * mesh.bindposes[index];
                    skinnedVertex += boneMatrix.MultiplyPoint3x4(vertex) * boneWeight.weight2;
                }
                index = boneWeight.boneIndex3;
                if (index > 0)
                {
                    bone = bones[index];
                    var boneMatrix = bone.localToWorldMatrix * mesh.bindposes[index];
                    skinnedVertex += boneMatrix.MultiplyPoint3x4(vertex) * boneWeight.weight3;
                }
                vertices[i] = skinnedVertex;
            }
            skinnedMesh.vertices = vertices;
            skinnedMesh.RecalculateBounds();
            skinnedMesh.RecalculateNormals();
        }

        void Update()
        {

#if UNITY_EDITOR
            if (Application.isPlaying)
                DrawSkinMesh();
            else
                Graphics.DrawMesh(mesh, transform.localToWorldMatrix, material, 0, null, 0, null, castShadow, receiveShadow, useLightProbes);
#else
            DrawSkinMesh();
#endif
        }

        private void DrawSkinMesh()
        {
            UpdateVertices();
            Graphics.DrawMesh(skinnedMesh, transform.localToWorldMatrix, material, 0, null, 0, null, castShadow, receiveShadow, useLightProbes);
        }
    }
}