three.js 把geometry转换成BufferGeometry，计算tangents

一、geometry=>buffergeomerty

var bufferGeometry = new THREE.BufferGeometry().fromGeometry( geometry );

threejs官方文档：https://threejs.org/docs/index.html#api/en/core/BufferGeometry.fromGeometry

二，计算Tangents

threejs官方文档：https://threejs.org/docs/index.html#examples/utils/BufferGeometryUtils