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

( function () {

	var SavePass = function ( renderTarget ) {

		THREE.Pass.call( this );
		if ( THREE.CopyShader === undefined ) console.error( 'THREE.SavePass relies on THREE.CopyShader' );
		var shader = THREE.CopyShader;
		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.renderTarget = new THREE.WebGLRenderTarget( window.innerWidth, window.innerHeight, {
				minFilter: THREE.LinearFilter,
				magFilter: THREE.LinearFilter,
				format: THREE.RGBFormat
			} );
			this.renderTarget.texture.name = 'SavePass.rt';

		}

		this.needsSwap = false;
		this.fsQuad = new THREE.Pass.FullScreenQuad( this.material );

	};

	SavePass.prototype = Object.assign( Object.create( THREE.Pass.prototype ), {
		constructor: SavePass,
		render: function ( renderer, writeBuffer, readBuffer ) {

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

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

			}

			renderer.setRenderTarget( this.renderTarget );
			if ( this.clear ) renderer.clear();
			this.fsQuad.render( renderer );

		}
	} );

	THREE.SavePass = SavePass;

} )();