Three.js設置背景透明

1.第一步，需要註釋場景背景色,否則會影響背景設置透明
var scene = new THREE.Scene();
scene.background = new THREE.Color( 0xa0a0a0 );
2.設置alpha透明係數
var renderer = new THREE.WebGLRenderer( { alpha: true } );
renderer.setClearAlpha(0);