three.js/examples/js/postprocessing/SavePass.js

/**
 * @author alteredq / http://alteredqualia.com/
 */

THREE.SavePass = function( renderTarget ) {

	var shader = THREE.ShaderExtras[ "screen" ];

	this.textureID = "tDiffuse";

	this.uniforms = THREE.UniformsUtils.clone( shader.uniforms );

	this.material = new THREE.ShaderMaterial( {

		uniforms: this.uniforms,
		vertexShader: shader.vertexShader,
		fragmentShader: shader.fragmentShader

	} );

	this.renderTarget = renderTarget;

	if ( this.renderTarget === undefined ) {

		this.renderTargetParameters = { minFilter: THREE.LinearFilter, magFilter: THREE.LinearFilter, format: THREE.RGBFormat, stencilBuffer: false };
		this.renderTarget = new THREE.WebGLRenderTarget( window.innerWidth, window.innerHeight, this.renderTargetParameters );

	}

	this.enabled = true;
	this.needsSwap = false;
	this.clear = false;

};

THREE.SavePass.prototype = {

	render: function ( renderer, writeBuffer, readBuffer, delta ) {

		if ( this.uniforms[ this.textureID ] ) {

			this.uniforms[ this.textureID ].texture = readBuffer;

		}

		THREE.EffectComposer.quad.material = this.material;

		renderer.render( THREE.EffectComposer.scene, THREE.EffectComposer.camera, this.renderTarget, this.clear );

	}

};