THREE.Reflector = function ( geometry, options ) {

	THREE.Mesh.call( this, geometry );

	this.type = 'Reflector';

	var scope = this;

	options = options || {};

	var color = ( options.color !== undefined ) ? new THREE.Color( options.color ) : new THREE.Color( 0x7F7F7F );
	var textureWidth = options.textureWidth || 512;
	var textureHeight = options.textureHeight || 512;
	var clipBias = options.clipBias || 0;
	var shader = options.shader || THREE.Reflector.ReflectorShader;

	//

	var reflectorPlane = new THREE.Plane();
	var normal = new THREE.Vector3();
	var reflectorWorldPosition = new THREE.Vector3();
	var cameraWorldPosition = new THREE.Vector3();
	var rotationMatrix = new THREE.Matrix4();
	var lookAtPosition = new THREE.Vector3( 0, 0, - 1 );
	var clipPlane = new THREE.Vector4();
	var viewport = new THREE.Vector4();

	var view = new THREE.Vector3();
	var target = new THREE.Vector3();
	var q = new THREE.Vector4();

	var textureMatrix = new THREE.Matrix4();
	var virtualCamera = new THREE.PerspectiveCamera();

	var parameters = {
		minFilter: THREE.LinearFilter,
		magFilter: THREE.LinearFilter,
		format: THREE.RGBFormat,
		stencilBuffer: false
	};

	var renderTarget = new THREE.WebGLRenderTarget( textureWidth, textureHeight, parameters );
	
	renderTarget.depthBuffer = true;
	renderTarget.depthTexture = new THREE.DepthTexture();
	renderTarget.depthTexture.type = THREE.UnsignedShortType;

	if ( ! THREE.Math.isPowerOfTwo( textureWidth ) || ! THREE.Math.isPowerOfTwo( textureHeight ) ) {

		renderTarget.texture.generateMipmaps = false;

	}

	var material = new THREE.ShaderMaterial( {
		uniforms: THREE.UniformsUtils.clone( shader.uniforms ),
		fragmentShader: shader.fragmentShader,
		vertexShader: shader.vertexShader,
		transparent: true
	} );

	material.uniforms.tDiffuse.value = renderTarget.texture;
	material.uniforms.tDepth.value = renderTarget.depthTexture;
	material.uniforms.color.value = color;
	material.uniforms.textureMatrix.value = textureMatrix;

	this.material = material;

	this.onBeforeRender = function ( renderer, scene, camera ) {

		reflectorWorldPosition.setFromMatrixPosition( scope.matrixWorld );
		cameraWorldPosition.setFromMatrixPosition( camera.matrixWorld );

		rotationMatrix.extractRotation( scope.matrixWorld );

		normal.set( 0, 0, 1 );
		normal.applyMatrix4( rotationMatrix );

		view.subVectors( reflectorWorldPosition, cameraWorldPosition );

		// Avoid rendering when reflector is facing away

		if ( view.dot( normal ) > 0 ) return;

		view.reflect( normal ).negate();
		view.add( reflectorWorldPosition );

		rotationMatrix.extractRotation( camera.matrixWorld );

		lookAtPosition.set( 0, 0, - 1 );
		lookAtPosition.applyMatrix4( rotationMatrix );
		lookAtPosition.add( cameraWorldPosition );

		target.subVectors( reflectorWorldPosition, lookAtPosition );
		target.reflect( normal ).negate();
		target.add( reflectorWorldPosition );

		virtualCamera.position.copy( view );
		virtualCamera.up.set( 0, 1, 0 );
		virtualCamera.up.applyMatrix4( rotationMatrix );
		virtualCamera.up.reflect( normal );
		virtualCamera.lookAt( target );

		virtualCamera.far = camera.far; // Used in WebGLBackground

		virtualCamera.updateMatrixWorld();
		virtualCamera.projectionMatrix.copy( camera.projectionMatrix );

		this.material.uniforms.cameraNear.value = camera.near;
		this.material.uniforms.cameraFar.value = camera.far;

		// Update the texture matrix
		textureMatrix.set(
			0.5, 0.0, 0.0, 0.5,
			0.0, 0.5, 0.0, 0.5,
			0.0, 0.0, 0.5, 0.5,
			0.0, 0.0, 0.0, 1.0
		);
		textureMatrix.multiply( virtualCamera.projectionMatrix );
		textureMatrix.multiply( virtualCamera.matrixWorldInverse );
		textureMatrix.multiply( scope.matrixWorld );

		// Now update projection matrix with new clip plane, implementing code from: http://www.terathon.com/code/oblique.html
		// Paper explaining this technique: http://www.terathon.com/lengyel/Lengyel-Oblique.pdf
		reflectorPlane.setFromNormalAndCoplanarPoint( normal, reflectorWorldPosition );
		reflectorPlane.applyMatrix4( virtualCamera.matrixWorldInverse );

		clipPlane.set( reflectorPlane.normal.x, reflectorPlane.normal.y, reflectorPlane.normal.z, reflectorPlane.constant );

		var projectionMatrix = virtualCamera.projectionMatrix;

		q.x = ( Math.sign( clipPlane.x ) + projectionMatrix.elements[ 8 ] ) / projectionMatrix.elements[ 0 ];
		q.y = ( Math.sign( clipPlane.y ) + projectionMatrix.elements[ 9 ] ) / projectionMatrix.elements[ 5 ];
		q.z = - 1.0;
		q.w = ( 1.0 + projectionMatrix.elements[ 10 ] ) / projectionMatrix.elements[ 14 ];

		// Calculate the scaled plane vector
		clipPlane.multiplyScalar( 2.0 / clipPlane.dot( q ) );

		// Replacing the third row of the projection matrix
		projectionMatrix.elements[ 2 ] = clipPlane.x;
		projectionMatrix.elements[ 6 ] = clipPlane.y;
		projectionMatrix.elements[ 10 ] = clipPlane.z + 1.0 - clipBias;
		projectionMatrix.elements[ 14 ] = clipPlane.w;

		// Render

		renderTarget.texture.encoding = renderer.outputEncoding;

		scope.visible = false;

		var currentRenderTarget = renderer.getRenderTarget();

		var currentXrEnabled = renderer.xr.enabled;
		var currentShadowAutoUpdate = renderer.shadowMap.autoUpdate;

		renderer.xr.enabled = false; // Avoid camera modification
		renderer.shadowMap.autoUpdate = false; // Avoid re-computing shadows

		renderer.setRenderTarget( renderTarget );

		renderer.state.buffers.depth.setMask( true ); // make sure the depth buffer is writable so it can be properly cleared, see #18897

		if ( renderer.autoClear === false ) renderer.clear();
		renderer.render( scene, virtualCamera );

		renderer.xr.enabled = currentXrEnabled;
		renderer.shadowMap.autoUpdate = currentShadowAutoUpdate;

		renderer.setRenderTarget( currentRenderTarget );
		// Restore viewport

		var bounds = camera.bounds;

		if ( bounds !== undefined ) {

			var size = renderer.getSize();
			var pixelRatio = renderer.getPixelRatio();

			viewport.x = bounds.x * size.width * pixelRatio;
			viewport.y = bounds.y * size.height * pixelRatio;
			viewport.z = bounds.z * size.width * pixelRatio;
			viewport.w = bounds.w * size.height * pixelRatio;

			renderer.state.viewport( viewport );

		}

		scope.visible = true;

	};

	this.getRenderTarget = function () {

		return renderTarget;

	};

};

THREE.Reflector.prototype = Object.create( THREE.Mesh.prototype );
THREE.Reflector.prototype.constructor = THREE.Reflector;

THREE.Reflector.ReflectorShader = {

	uniforms: {

		'color': {
			type: 'c',
			value: null
		},

		'tDiffuse': {
			type: 't',
			value: null
		},
		
		'tDepth': {
			type: 't',
			value: null
		},

		'textureMatrix': {
			type: 'm4',
			value: null
		},
		
		'cameraNear': {
			type: 'f',
			value: 0
		},
		
		'cameraFar': {
			type: 'f',
			value: 0
		},

	},

	vertexShader: [
		'uniform mat4 textureMatrix;',
		'varying vec4 vUv;',

		'void main() {',

		'	vUv = textureMatrix * vec4( position, 1.0 );',

		'	gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );',

		'}'
	].join( '\n' ),

	fragmentShader: [
		'#include <packing>',
		'uniform vec3 color;',
		'uniform sampler2D tDiffuse;',
		'uniform sampler2D tDepth;',
		'uniform float cameraNear;',
		'uniform float cameraFar;',
		'varying vec4 vUv;',

		'float blendOverlay( float base, float blend ) {',

		'	return( base < 0.5 ? ( 2.0 * base * blend ) : ( 1.0 - 2.0 * ( 1.0 - base ) * ( 1.0 - blend ) ) );',

		'}',

		'vec3 blendOverlay( vec3 base, vec3 blend ) {',

		'	return vec3( blendOverlay( base.r, blend.r ), blendOverlay( base.g, blend.g ), blendOverlay( base.b, blend.b ) );',

		'}',
		
		'float readDepth( sampler2D depthSampler, vec4 coord ) {',
				
		'	float fragCoordZ = texture2DProj( depthSampler, coord ).x;',
		'	float viewZ = perspectiveDepthToViewZ( fragCoordZ, cameraNear, cameraFar );',
		'	return viewZToOrthographicDepth( viewZ, cameraNear, cameraFar );',
			
		'}',

		'void main() {',

		'	vec4 base = texture2DProj( tDiffuse, vUv );',
		' float depth = readDepth( tDepth, vUv );',
		'	gl_FragColor = vec4( blendOverlay( base.rgb, color ), 1.0 - ( depth * 7000.0 ) );',

		'}'
	].join( '\n' )
};