将场景作为纹理渲染到平面上

firstRenderTarget = new THREE.WebGLRenderTarget( 512, 512, { format: THREE.RGBFormat } ); 

var screenMaterial = new THREE.MeshBasicMaterial( { map: firstRenderTarget } );

renderer.render( scene, textureCamera, firstRenderTarget, true );

textureCamera 设置了采集场景用的相机的姿态，最终渲染的结果放在firstRenderTarget

FYI:

https://stemkoski.github.io/Three.js/Camera-Texture.html