Three.js中如何从名为“小河”的几何体提取单个面的形状信息？

<code class="javascript">const waterGeometry = this.scene.getObjectByName('小河');
if (waterGeometry.geometry instanceof THREE.Geometry) {
  const faces = waterGeometry.geometry.faces;
  // 假设我们想获取第一个面的信息 (索引为 0)
  const face = faces[0];
  const vertexA = waterGeometry.geometry.vertices[face.a];
  const vertexB = waterGeometry.geometry.vertices[face.b];
  const vertexC = waterGeometry.geometry.vertices[face.c];

  // vertexA, vertexB, vertexC 现在包含了该面的三个顶点坐标 (THREE.Vector3)
  console.log("Face 0 vertices:", vertexA, vertexB, vertexC);
} else if (waterGeometry.geometry instanceof THREE.BufferGeometry) {
  // 对于THREE.BufferGeometry类型，需要处理index属性
  const indexAttribute = waterGeometry.geometry.getIndex();
  const positionAttribute = waterGeometry.geometry.getAttribute('position');
  // 假设我们想获取第一个面的信息，需要根据index属性确定顶点索引
  const faceIndex = 0;  // 这里需要根据你的BufferGeometry的结构确定正确的faceIndex
  const startIndex = faceIndex * 3; // 每个面三个顶点
  const vertexA = new THREE.Vector3().fromBufferAttribute(positionAttribute, startIndex);
  const vertexB = new THREE.Vector3().fromBufferAttribute(positionAttribute, startIndex + 1);
  const vertexC = new THREE.Vector3().fromBufferAttribute(positionAttribute, startIndex + 2);

  console.log("Face 0 vertices:", vertexA, vertexB, vertexC);
} else {
  console.error("Unsupported geometry type.");
}</code>