Three.js设置背景透明

1.第一步，需要注释场景背景色,否则会影响背景设置透明
var scene = new THREE.Scene();
scene.background = new THREE.Color( 0xa0a0a0 );
2.设置alpha透明系数
var renderer = new THREE.WebGLRenderer( { alpha: true } );
renderer.setClearAlpha(0);