three.js/examples/js/postprocessing/CubeTexturePass.js

( function () {

	var CubeTexturePass = function ( camera, envMap, opacity ) {

		THREE.Pass.call( this );
		this.camera = camera;
		this.needsSwap = false;
		this.cubeShader = THREE.ShaderLib[ 'cube' ];
		this.cubeMesh = new THREE.Mesh( new THREE.BoxGeometry( 10, 10, 10 ), new THREE.ShaderMaterial( {
			uniforms: THREE.UniformsUtils.clone( this.cubeShader.uniforms ),
			vertexShader: this.cubeShader.vertexShader,
			fragmentShader: this.cubeShader.fragmentShader,
			depthTest: false,
			depthWrite: false,
			side: THREE.BackSide
		} ) );
		Object.defineProperty( this.cubeMesh.material, 'envMap', {
			get: function () {

				return this.uniforms.envMap.value;

			}
		} );
		this.envMap = envMap;
		this.opacity = opacity !== undefined ? opacity : 1.0;
		this.cubeScene = new THREE.Scene();
		this.cubeCamera = new THREE.PerspectiveCamera();
		this.cubeScene.add( this.cubeMesh );

	};

	CubeTexturePass.prototype = Object.assign( Object.create( THREE.Pass.prototype ), {
		constructor: CubeTexturePass,
		render: function ( renderer, writeBuffer, readBuffer
			/*, deltaTime, maskActive*/
		) {

			var oldAutoClear = renderer.autoClear;
			renderer.autoClear = false;
			this.cubeCamera.projectionMatrix.copy( this.camera.projectionMatrix );
			this.cubeCamera.quaternion.setFromRotationMatrix( this.camera.matrixWorld );
			this.cubeMesh.material.uniforms.envMap.value = this.envMap;
			this.cubeMesh.material.uniforms.flipEnvMap.value = this.envMap.isCubeTexture && this.envMap._needsFlipEnvMap ? - 1 : 1;
			this.cubeMesh.material.uniforms.opacity.value = this.opacity;
			this.cubeMesh.material.transparent = this.opacity < 1.0;
			renderer.setRenderTarget( this.renderToScreen ? null : readBuffer );
			if ( this.clear ) renderer.clear();
			renderer.render( this.cubeScene, this.cubeCamera );
			renderer.autoClear = oldAutoClear;

		}
	} );

	THREE.CubeTexturePass = CubeTexturePass;

} )();