three.js/examples/js/effects/CardboardEffect.js

/**
 * @author mrdoob / http://mrdoob.com/
 */

THREE.CardboardEffect = function ( renderer ) {

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

	var _scene = new THREE.Scene();

	var _stereo = new THREE.StereoCamera();
	_stereo.aspect = 0.5;

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

	var _renderTarget = new THREE.WebGLRenderTarget( 512, 512, _params );
	_renderTarget.scissorTest = true;

	// Distortion Mesh ported from:
	// https://github.com/borismus/webvr-boilerplate/blob/master/src/distortion/barrel-distortion-fragment.js

	var distortion = new THREE.Vector2( 0.441, 0.156 );

	var geometry = new THREE.PlaneBufferGeometry( 1, 1, 10, 20 );

	var indices = geometry.index.array;
	var positions = geometry.attributes.position.array;
	var uvs = geometry.attributes.uv.array;

	var vector = new THREE.Vector2();

	function poly( val ) {

		return 1.5 + ( distortion.x + distortion.y * val ) * val;

	}

	for ( var i = 0; i < indices.length; i ++ ) {

		vector.x = positions[ i * 3 + 0 ];
		vector.y = positions[ i * 3 + 1 ];

		var scalar = poly( vector.dot( vector ) );

		positions[ i * 3 + 0 ] = ( vector.x / scalar ) * 1.5 - 0.5;
		positions[ i * 3 + 1 ] = ( vector.y / scalar ) * 3.0;

		uvs[ i * 2 ] *= 0.5;

	}

	// clone geometry

	function copyArray( array1, array2, offset ) {

		for ( var i = 0, l = array2.length; i < l; i ++ ) {

			array1[ i + offset ] = array2[ i ];

		}

	}

	var indices2 = new Uint16Array( indices.length * 2 );
	var positions2 = new Float32Array( positions.length * 2 );
	var uvs2 = new Float32Array( uvs.length * 2 );

	copyArray( indices2, indices, 0 );
	copyArray( positions2, positions, 0 );
	copyArray( uvs2, uvs, 0 );

	var offset = positions.length / 3;

	for ( i = 0; i < indices.length; i ++ ) {

		indices[ i ] += offset;
		positions[ i * 3 ] += 1.0;
		uvs[ i * 2 ] += 0.5;

	}

	copyArray( indices2, indices, indices.length );
	copyArray( positions2, positions, positions.length );
	copyArray( uvs2, uvs, uvs.length );

	var geometry2 = new THREE.BufferGeometry();
	geometry2.setIndex( new THREE.BufferAttribute( indices2, 1 ) );
	geometry2.addAttribute( 'position', new THREE.BufferAttribute( positions2, 3 ) );
	geometry2.addAttribute( 'uv', new THREE.BufferAttribute( uvs2, 2 ) );

	// var material = new THREE.MeshBasicMaterial( { wireframe: true } );
	var material = new THREE.MeshBasicMaterial( { map: _renderTarget } );
	var mesh = new THREE.Mesh( geometry2, material );
	_scene.add( mesh );

	//

	this.setSize = function ( width, height ) {

		_renderTarget.setSize( width, height );

		renderer.setSize( width, height );

	};

	this.render = function ( scene, camera ) {

		scene.updateMatrixWorld();

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

		_stereo.update( camera );

		var width = _renderTarget.width / 2;
		var height = _renderTarget.height;

		_renderTarget.scissor.set( 0, 0, width, height );
		_renderTarget.viewport.set( 0, 0, width, height );
		renderer.render( scene, _stereo.cameraL, _renderTarget );

		_renderTarget.scissor.set( width, 0, width, height );
		_renderTarget.viewport.set( width, 0, width, height );
		renderer.render( scene, _stereo.cameraR, _renderTarget );

		renderer.render( _scene, _camera );

	};

};