在Three.js中获取人脸全局法线

// 导入Three.js库和相关依赖
import * as THREE from 'three';

// 创建场景和相机
const scene = new THREE.Scene();
const camera = new THREE.PerspectiveCamera(75, window.innerWidth / window.innerHeight, 0.1, 1000);

// 导入模型
const loader = new THREE.OBJLoader();
loader.load('path/to/model.obj', function (object) {
  // 计算法线
  object.traverse(function (child) {
    if (child instanceof THREE.Mesh) {
      child.geometry.computeFaceNormals();
      child.geometry.computeVertexNormals();
    }
  });

  // 获取全局法线
  object.traverse(function (child) {
    if (child instanceof THREE.Mesh) {
      const vertexNormals = child.geometry.getAttribute('normal');
      const faceNormals = child.geometry.faces.map(face => face.normal);

      for (let i = 0; i < vertexNormals.count; i++) {
        const vertexNormal = vertexNormals.array.slice(i * 3, i * 3 + 3);
        const adjacentFaceNormals = [];

        child.geometry.faces.forEach(face => {
          if (face.a === i || face.b === i || face.c === i) {
            adjacentFaceNormals.push(face.normal);
          }
        });

        const globalNormal = averageNormals(vertexNormal, adjacentFaceNormals);
        vertexNormals.array.set(globalNormal, i * 3);
      }

      vertexNormals.needsUpdate = true;
    }
  });

  // 使用全局法线
  const material = new THREE.MeshPhongMaterial({ color: 0x00ff00 });
  object.traverse(function (child) {
    if (child instanceof THREE.Mesh) {
      child.material = material;
    }
  });

  scene.add(object);
});

// 渲染场景
const renderer = new THREE.WebGLRenderer();
renderer.setSize(window.innerWidth, window.innerHeight);
document.body.appendChild(renderer.domElement);

function animate() {
  requestAnimationFrame(animate);
  renderer.render(scene, camera);
}

animate();

// 辅助函数：计算法线的平均值
function averageNormals(vertexNormal, faceNormals) {
  const sum = vertexNormal.slice();
  faceNormals.forEach(normal => {
    sum[0] += normal.x;
    sum[1] += normal.y;
    sum[2] += normal.z;
  });

  const count = faceNormals.length + 1;
  return [sum[0] / count, sum[1] / count, sum[2] / count];
}