three.js/examples/js/effects/ParallaxBarrierEffect.js

THREE.ParallaxBarrierEffect = function ( renderer ) {

	var _camera = new THREE.OrthographicCamera( - 1, 1, 1, - 1, 0, 1 );

	var _scene = new THREE.Scene();

	var _stereo = new THREE.StereoCamera();

	var _params = { minFilter: THREE.LinearFilter, magFilter: THREE.NearestFilter, format: THREE.RGBAFormat };

	var _renderTargetL = new THREE.WebGLRenderTarget( 512, 512, _params );
	var _renderTargetR = new THREE.WebGLRenderTarget( 512, 512, _params );

	var _material = new THREE.ShaderMaterial( {

		uniforms: {

			'mapLeft': { value: _renderTargetL.texture },
			'mapRight': { value: _renderTargetR.texture }

		},

		vertexShader: [

			'varying vec2 vUv;',

			'void main() {',

			'	vUv = vec2( uv.x, uv.y );',
			'	gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );',

			'}'

		].join( '\n' ),

		fragmentShader: [

			'uniform sampler2D mapLeft;',
			'uniform sampler2D mapRight;',
			'varying vec2 vUv;',

			'void main() {',

			'	vec2 uv = vUv;',

			'	if ( ( mod( gl_FragCoord.y, 2.0 ) ) > 1.00 ) {',

			'		gl_FragColor = texture2D( mapLeft, uv );',

			'	} else {',

			'		gl_FragColor = texture2D( mapRight, uv );',

			'	}',

			'}'

		].join( '\n' )

	} );

	var mesh = new THREE.Mesh( new THREE.PlaneGeometry( 2, 2 ), _material );
	_scene.add( mesh );

	this.setSize = function ( width, height ) {

		renderer.setSize( width, height );

		var pixelRatio = renderer.getPixelRatio();

		_renderTargetL.setSize( width * pixelRatio, height * pixelRatio );
		_renderTargetR.setSize( width * pixelRatio, height * pixelRatio );

	};

	this.render = function ( scene, camera ) {

		scene.updateMatrixWorld();

		if ( camera.parent === null ) camera.updateMatrixWorld();

		_stereo.update( camera );

		renderer.setRenderTarget( _renderTargetL );
		renderer.clear();
		renderer.render( scene, _stereo.cameraL );

		renderer.setRenderTarget( _renderTargetR );
		renderer.clear();
		renderer.render( scene, _stereo.cameraR );

		renderer.setRenderTarget( null );
		renderer.render( _scene, _camera );

	};

};