three.js/examples/js/effects/AnaglyphEffect.js

( function () {

	var AnaglyphEffect = function ( renderer, width, height ) {

		// Dubois matrices from https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.7.6968&rep=rep1&type=pdf#page=4
		this.colorMatrixLeft = new THREE.Matrix3().fromArray( [ 0.456100, - 0.0400822, - 0.0152161, 0.500484, - 0.0378246, - 0.0205971, 0.176381, - 0.0157589, - 0.00546856 ] );
		this.colorMatrixRight = new THREE.Matrix3().fromArray( [ - 0.0434706, 0.378476, - 0.0721527, - 0.0879388, 0.73364, - 0.112961, - 0.00155529, - 0.0184503, 1.2264 ] );

		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
		};
		if ( width === undefined ) width = 512;
		if ( height === undefined ) height = 512;

		var _renderTargetL = new THREE.WebGLRenderTarget( width, height, _params );

		var _renderTargetR = new THREE.WebGLRenderTarget( width, height, _params );

		var _material = new THREE.ShaderMaterial( {
			uniforms: {
				'mapLeft': {
					value: _renderTargetL.texture
				},
				'mapRight': {
					value: _renderTargetR.texture
				},
				'colorMatrixLeft': {
					value: this.colorMatrixLeft
				},
				'colorMatrixRight': {
					value: this.colorMatrixRight
				}
			},
			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;', 'uniform mat3 colorMatrixLeft;', 'uniform mat3 colorMatrixRight;', // These functions implement sRGB linearization and gamma correction
				'float lin( float c ) {', '	return c <= 0.04045 ? c * 0.0773993808 :', '			pow( c * 0.9478672986 + 0.0521327014, 2.4 );', '}', 'vec4 lin( vec4 c ) {', '	return vec4( lin( c.r ), lin( c.g ), lin( c.b ), c.a );', '}', 'float dev( float c ) {', '	return c <= 0.0031308 ? c * 12.92', '			: pow( c, 0.41666 ) * 1.055 - 0.055;', '}', 'void main() {', '	vec2 uv = vUv;', '	vec4 colorL = lin( texture2D( mapLeft, uv ) );', '	vec4 colorR = lin( texture2D( mapRight, uv ) );', '	vec3 color = clamp(', '			colorMatrixLeft * colorL.rgb +', '			colorMatrixRight * colorR.rgb, 0., 1. );', '	gl_FragColor = vec4(', '			dev( color.r ), dev( color.g ), dev( color.b ),', '			max( colorL.a, colorR.a ) );', '}' ].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 ) {

			var currentRenderTarget = renderer.getRenderTarget();
			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 );
			renderer.setRenderTarget( currentRenderTarget );

		};

		this.dispose = function () {

			if ( _renderTargetL ) _renderTargetL.dispose();
			if ( _renderTargetR ) _renderTargetR.dispose();
			if ( _mesh ) _mesh.geometry.dispose();
			if ( _material ) _material.dispose();

		};

	};

	THREE.AnaglyphEffect = AnaglyphEffect;

} )();