/**
 * @author Emmett Lalish / elalish
 *
 * This class generates a Prefiltered, Mipmapped Radiance Environment Map
 * (PMREM) from a cubeMap environment texture. This allows different levels of
 * blur to be quickly accessed based on material roughness. It is packed into a
 * special CubeUV format that allows us to perform custom interpolation so that
 * we can support nonlinear formats such as RGBE. Unlike a traditional mipmap
 * chain, it only goes down to the LOD_MIN level (above), and then creates extra
 * even more filtered 'mips' at the same LOD_MIN resolution, associated with
 * higher roughness levels. In this way we maintain resolution to smoothly
 * interpolate diffuse lighting while limiting sampling computation.
 */

import {
	CubeUVReflectionMapping,
	GammaEncoding,
	LinearEncoding,
	LinearToneMapping,
	NearestFilter,
	NoBlending,
	RGBDEncoding,
	RGBEEncoding,
	RGBEFormat,
	RGBM16Encoding,
	RGBM7Encoding,
	UnsignedByteType,
	sRGBEncoding
} from "../constants.js";

import { BufferAttribute } from "../core/BufferAttribute.js";
import { BufferGeometry } from "../core/BufferGeometry.js";
import { Mesh } from "../objects/Mesh.js";
import { OrthographicCamera } from "../cameras/OrthographicCamera.js";
import { PerspectiveCamera } from "../cameras/PerspectiveCamera.js";
import { RawShaderMaterial } from "../materials/RawShaderMaterial.js";
import { Scene } from "../scenes/Scene.js";
import { Vector2 } from "../math/Vector2.js";
import { Vector3 } from "../math/Vector3.js";
import { WebGLRenderTarget } from "../renderers/WebGLRenderTarget.js";

var LOD_MIN = 4;
var LOD_MAX = 8;
var SIZE_MAX = Math.pow( 2, LOD_MAX );

// The standard deviations (radians) associated with the extra mips. These are
// chosen to approximate a Trowbridge-Reitz distribution function times the
// geometric shadowing function. These sigma values squared must match the
// variance #defines in cube_uv_reflection_fragment.glsl.js.
var EXTRA_LOD_SIGMA = [ 0.125, 0.215, 0.35, 0.446, 0.526, 0.582 ];

var TOTAL_LODS = LOD_MAX - LOD_MIN + 1 + EXTRA_LOD_SIGMA.length;

// The maximum length of the blur for loop. Smaller sigmas will use fewer
// samples and exit early, but not recompile the shader.
var MAX_SAMPLES = 20;

var ENCODINGS = {
	[ LinearEncoding ]: 0,
	[ sRGBEncoding ]: 1,
	[ RGBEEncoding ]: 2,
	[ RGBM7Encoding ]: 3,
	[ RGBM16Encoding ]: 4,
	[ RGBDEncoding ]: 5,
	[ GammaEncoding ]: 6
};

var _flatCamera = new OrthographicCamera();
var { _lodPlanes, _sizeLods, _sigmas } = _createPlanes();
var _oldTarget = null;

// Golden Ratio
var PHI = ( 1 + Math.sqrt( 5 ) ) / 2;
var INV_PHI = 1 / PHI;

// Vertices of a dodecahedron (except the opposites, which represent the
// same axis), used as axis directions evenly spread on a sphere.
var _axisDirections = [
	new Vector3( 1, 1, 1 ),
	new Vector3( - 1, 1, 1 ),
	new Vector3( 1, 1, - 1 ),
	new Vector3( - 1, 1, - 1 ),
	new Vector3( 0, PHI, INV_PHI ),
	new Vector3( 0, PHI, - INV_PHI ),
	new Vector3( INV_PHI, 0, PHI ),
	new Vector3( - INV_PHI, 0, PHI ),
	new Vector3( PHI, INV_PHI, 0 ),
	new Vector3( - PHI, INV_PHI, 0 ) ];

function PMREMGenerator( renderer ) {

	this._renderer = renderer;
	this._pingPongRenderTarget = null;

	this._blurMaterial = _getBlurShader( MAX_SAMPLES );
	this._equirectShader = null;
	this._cubemapShader = null;

	this._compileMaterial( this._blurMaterial );

}

PMREMGenerator.prototype = {

	constructor: PMREMGenerator,

	/**
	 * Generates a PMREM from a supplied Scene, which can be faster than using an
	 * image if networking bandwidth is low. Optional sigma specifies a blur radius
	 * in radians to be applied to the scene before PMREM generation. Optional near
	 * and far planes ensure the scene is rendered in its entirety (the cubeCamera
	 * is placed at the origin).
	 */
	fromScene: function ( scene, sigma = 0, near = 0.1, far = 100 ) {

		_oldTarget = this._renderer.getRenderTarget();
		var cubeUVRenderTarget = this._allocateTargets();

		this._sceneToCubeUV( scene, near, far, cubeUVRenderTarget );
		if ( sigma > 0 ) {

			this._blur( cubeUVRenderTarget, 0, 0, sigma );

		}

		this._applyPMREM( cubeUVRenderTarget );
		this._cleanup( cubeUVRenderTarget );

		return cubeUVRenderTarget;

	},

	/**
	 * Generates a PMREM from an equirectangular texture, which can be either LDR
	 * (RGBFormat) or HDR (RGBEFormat). The ideal input image size is 1k (1024 x 512),
	 * as this matches best with the 256 x 256 cubemap output.
	 */
	fromEquirectangular: function ( equirectangular ) {

		equirectangular.magFilter = NearestFilter;
		equirectangular.minFilter = NearestFilter;
		equirectangular.generateMipmaps = false;

		return this.fromCubemap( equirectangular );

	},

	/**
	 * Generates a PMREM from an cubemap texture, which can be either LDR
	 * (RGBFormat) or HDR (RGBEFormat). The ideal input cube size is 256 x 256,
	 * as this matches best with the 256 x 256 cubemap output.
	 */
	fromCubemap: function ( cubemap ) {

		_oldTarget = this._renderer.getRenderTarget();
		var cubeUVRenderTarget = this._allocateTargets( cubemap );
		this._textureToCubeUV( cubemap, cubeUVRenderTarget );
		this._applyPMREM( cubeUVRenderTarget );
		this._cleanup( cubeUVRenderTarget );

		return cubeUVRenderTarget;

	},

	/**
	 * Pre-compiles the cubemap shader. You can get faster start-up by invoking this method during
	 * your texture's network fetch for increased concurrency.
	 */
	compileCubemapShader: function () {

		if ( this._cubemapShader === null ) {

			this._cubemapShader = _getCubemapShader();
			this._compileMaterial( this._cubemapShader );

		}

	},

	/**
	 * Pre-compiles the equirectangular shader. You can get faster start-up by invoking this method during
	 * your texture's network fetch for increased concurrency.
	 */
	compileEquirectangularShader: function () {

		if ( this._equirectShader === null ) {

			this._equirectShader = _getEquirectShader();
			this._compileMaterial( this._equirectShader );

		}

	},

	/**
	 * Disposes of the PMREMGenerator's internal memory. Note that PMREMGenerator is a static class,
	 * so you should not need more than one PMREMGenerator object. If you do, calling dispose() on
	 * one of them will cause any others to also become unusable.
	 */
	dispose: function () {

		this._blurMaterial.dispose();

		if ( this._cubemapShader !== null ) this._cubemapShader.dispose();
		if ( this._equirectShader !== null ) this._equirectShader.dispose();

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

			_lodPlanes[ i ].dispose();

		}

	},

	// private interface

	_cleanup: function ( outputTarget ) {

		this._pingPongRenderTarget.dispose();
		this._renderer.setRenderTarget( _oldTarget );
		outputTarget.scissorTest = false;
		// reset viewport and scissor
		outputTarget.setSize( outputTarget.width, outputTarget.height );

	},

	_allocateTargets: function ( equirectangular ) {

		var params = {
			magFilter: NearestFilter,
			minFilter: NearestFilter,
			generateMipmaps: false,
			type: UnsignedByteType,
			format: RGBEFormat,
			encoding: _isLDR( equirectangular ) ? equirectangular.encoding : RGBEEncoding,
			depthBuffer: false,
			stencilBuffer: false
		};

		var cubeUVRenderTarget = _createRenderTarget( params );
		cubeUVRenderTarget.depthBuffer = equirectangular ? false : true;
		this._pingPongRenderTarget = _createRenderTarget( params );
		return cubeUVRenderTarget;

	},

	_compileMaterial: function ( material ) {

		var tmpScene = new Scene();
		tmpScene.add( new Mesh( _lodPlanes[ 0 ], material ) );
		this._renderer.compile( tmpScene, _flatCamera );

	},

	_sceneToCubeUV: function ( scene, near, far, cubeUVRenderTarget ) {

		var fov = 90;
		var aspect = 1;
		var cubeCamera = new PerspectiveCamera( fov, aspect, near, far );
		var upSign = [ 1, 1, 1, 1, - 1, 1 ];
		var forwardSign = [ 1, 1, - 1, - 1, - 1, 1 ];
		var renderer = this._renderer;

		var outputEncoding = renderer.outputEncoding;
		var toneMapping = renderer.toneMapping;
		var toneMappingExposure = renderer.toneMappingExposure;
		var clearColor = renderer.getClearColor();
		var clearAlpha = renderer.getClearAlpha();

		renderer.toneMapping = LinearToneMapping;
		renderer.toneMappingExposure = 1.0;
		renderer.outputEncoding = LinearEncoding;
		scene.scale.z *= - 1;

		var background = scene.background;
		if ( background && background.isColor ) {

			background.convertSRGBToLinear();
			// Convert linear to RGBE
			var maxComponent = Math.max( background.r, background.g, background.b );
			var fExp = Math.min( Math.max( Math.ceil( Math.log2( maxComponent ) ), - 128.0 ), 127.0 );
			background = background.multiplyScalar( Math.pow( 2.0, - fExp ) );
			var alpha = ( fExp + 128.0 ) / 255.0;
			renderer.setClearColor( background, alpha );
			scene.background = null;

		}

		for ( var i = 0; i < 6; i ++ ) {

			var col = i % 3;
			if ( col == 0 ) {

				cubeCamera.up.set( 0, upSign[ i ], 0 );
				cubeCamera.lookAt( forwardSign[ i ], 0, 0 );

			} else if ( col == 1 ) {

				cubeCamera.up.set( 0, 0, upSign[ i ] );
				cubeCamera.lookAt( 0, forwardSign[ i ], 0 );

			} else {

				cubeCamera.up.set( 0, upSign[ i ], 0 );
				cubeCamera.lookAt( 0, 0, forwardSign[ i ] );

			}

			_setViewport( cubeUVRenderTarget,
				col * SIZE_MAX, i > 2 ? SIZE_MAX : 0, SIZE_MAX, SIZE_MAX );
			renderer.setRenderTarget( cubeUVRenderTarget );
			renderer.render( scene, cubeCamera );

		}

		renderer.toneMapping = toneMapping;
		renderer.toneMappingExposure = toneMappingExposure;
		renderer.outputEncoding = outputEncoding;
		renderer.setClearColor( clearColor, clearAlpha );
		scene.scale.z *= - 1;

	},

	_textureToCubeUV: function ( texture, cubeUVRenderTarget ) {

		var scene = new Scene();
		var renderer = this._renderer;

		if ( texture.isCubeTexture ) {

			if ( this._cubemapShader == null ) {

				this._cubemapShader = _getCubemapShader();

			}

		} else {

			if ( this._equirectShader == null ) {

				this._equirectShader = _getEquirectShader();

			}

		}

		var material = texture.isCubeTexture ? this._cubemapShader : this._equirectShader;
		scene.add( new Mesh( _lodPlanes[ 0 ], material ) );

		var uniforms = material.uniforms;

		uniforms[ 'envMap' ].value = texture;

		if ( ! texture.isCubeTexture ) {

			uniforms[ 'texelSize' ].value.set( 1.0 / texture.image.width, 1.0 / texture.image.height );

		}

		uniforms[ 'inputEncoding' ].value = ENCODINGS[ texture.encoding ];
		uniforms[ 'outputEncoding' ].value = ENCODINGS[ cubeUVRenderTarget.texture.encoding ];

		_setViewport( cubeUVRenderTarget, 0, 0, 3 * SIZE_MAX, 2 * SIZE_MAX );

		renderer.setRenderTarget( cubeUVRenderTarget );
		renderer.render( scene, _flatCamera );

	},

	_applyPMREM: function ( cubeUVRenderTarget ) {

		var renderer = this._renderer;
		var autoClear = renderer.autoClear;
		renderer.autoClear = false;

		for ( var i = 1; i < TOTAL_LODS; i ++ ) {

			var sigma = Math.sqrt( _sigmas[ i ] * _sigmas[ i ] - _sigmas[ i - 1 ] * _sigmas[ i - 1 ] );

			var poleAxis = _axisDirections[ ( i - 1 ) % _axisDirections.length ];

			this._blur( cubeUVRenderTarget, i - 1, i, sigma, poleAxis );

		}

		renderer.autoClear = autoClear;

	},

	/**
	 * This is a two-pass Gaussian blur for a cubemap. Normally this is done
	 * vertically and horizontally, but this breaks down on a cube. Here we apply
	 * the blur latitudinally (around the poles), and then longitudinally (towards
	 * the poles) to approximate the orthogonally-separable blur. It is least
	 * accurate at the poles, but still does a decent job.
	 */
	_blur: function ( cubeUVRenderTarget, lodIn, lodOut, sigma, poleAxis ) {

		var pingPongRenderTarget = this._pingPongRenderTarget;

		this._halfBlur(
			cubeUVRenderTarget,
			pingPongRenderTarget,
			lodIn,
			lodOut,
			sigma,
			'latitudinal',
			poleAxis );

		this._halfBlur(
			pingPongRenderTarget,
			cubeUVRenderTarget,
			lodOut,
			lodOut,
			sigma,
			'longitudinal',
			poleAxis );

	},

	_halfBlur: function ( targetIn, targetOut, lodIn, lodOut, sigmaRadians, direction, poleAxis ) {

		var renderer = this._renderer;
		var blurMaterial = this._blurMaterial;

		if ( direction !== 'latitudinal' && direction !== 'longitudinal' ) {

			console.error(
				'blur direction must be either latitudinal or longitudinal!' );

		}

		// Number of standard deviations at which to cut off the discrete approximation.
		var STANDARD_DEVIATIONS = 3;

		var blurScene = new Scene();
		blurScene.add( new Mesh( _lodPlanes[ lodOut ], blurMaterial ) );
		var blurUniforms = blurMaterial.uniforms;

		var pixels = _sizeLods[ lodIn ] - 1;
		var radiansPerPixel = isFinite( sigmaRadians ) ? Math.PI / ( 2 * pixels ) : 2 * Math.PI / ( 2 * MAX_SAMPLES - 1 );
		var sigmaPixels = sigmaRadians / radiansPerPixel;
		var samples = isFinite( sigmaRadians ) ? 1 + Math.floor( STANDARD_DEVIATIONS * sigmaPixels ) : MAX_SAMPLES;

		if ( samples > MAX_SAMPLES ) {

			console.warn( `sigmaRadians, ${
				sigmaRadians}, is too large and will clip, as it requested ${
				samples} samples when the maximum is set to ${MAX_SAMPLES}` );

		}

		var weights = [];
		var sum = 0;

		for ( var i = 0; i < MAX_SAMPLES; ++ i ) {

			var x = i / sigmaPixels;
			var weight = Math.exp( - x * x / 2 );
			weights.push( weight );

			if ( i == 0 ) {

				sum += weight;

			} else if ( i < samples ) {

				sum += 2 * weight;

			}

		}

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

			weights[ i ] = weights[ i ] / sum;

		}

		blurUniforms[ 'envMap' ].value = targetIn.texture;
		blurUniforms[ 'samples' ].value = samples;
		blurUniforms[ 'weights' ].value = weights;
		blurUniforms[ 'latitudinal' ].value = direction === 'latitudinal';

		if ( poleAxis ) {

			blurUniforms[ 'poleAxis' ].value = poleAxis;

		}

		blurUniforms[ 'dTheta' ].value = radiansPerPixel;
		blurUniforms[ 'mipInt' ].value = LOD_MAX - lodIn;
		blurUniforms[ 'inputEncoding' ].value = ENCODINGS[ targetIn.texture.encoding ];
		blurUniforms[ 'outputEncoding' ].value = ENCODINGS[ targetIn.texture.encoding ];

		var outputSize = _sizeLods[ lodOut ];
		var x = 3 * Math.max( 0, SIZE_MAX - 2 * outputSize );
		var y = ( lodOut === 0 ? 0 : 2 * SIZE_MAX ) + 2 * outputSize * ( lodOut > LOD_MAX - LOD_MIN ? lodOut - LOD_MAX + LOD_MIN : 0 );

		_setViewport( targetOut, x, y, 3 * outputSize, 2 * outputSize );
		renderer.setRenderTarget( targetOut );
		renderer.render( blurScene, _flatCamera );

	}

};

function _isLDR( texture ) {

	if ( texture === undefined || texture.type !== UnsignedByteType ) return false;

	return texture.encoding === LinearEncoding || texture.encoding === sRGBEncoding || texture.encoding === GammaEncoding;

}

function _createPlanes() {

	var _lodPlanes = [];
	var _sizeLods = [];
	var _sigmas = [];

	var lod = LOD_MAX;

	for ( var i = 0; i < TOTAL_LODS; i ++ ) {

		var sizeLod = Math.pow( 2, lod );
		_sizeLods.push( sizeLod );
		var sigma = 1.0 / sizeLod;

		if ( i > LOD_MAX - LOD_MIN ) {

			sigma = EXTRA_LOD_SIGMA[ i - LOD_MAX + LOD_MIN - 1 ];

		} else if ( i == 0 ) {

			sigma = 0;

		}

		_sigmas.push( sigma );

		var texelSize = 1.0 / ( sizeLod - 1 );
		var min = - texelSize / 2;
		var max = 1 + texelSize / 2;
		var uv1 = [ min, min, max, min, max, max, min, min, max, max, min, max ];

		var cubeFaces = 6;
		var vertices = 6;
		var positionSize = 3;
		var uvSize = 2;
		var faceIndexSize = 1;

		var position = new Float32Array( positionSize * vertices * cubeFaces );
		var uv = new Float32Array( uvSize * vertices * cubeFaces );
		var faceIndex = new Float32Array( faceIndexSize * vertices * cubeFaces );

		for ( var face = 0; face < cubeFaces; face ++ ) {

			var x = ( face % 3 ) * 2 / 3 - 1;
			var y = face > 2 ? 0 : - 1;
			var coordinates = [
				x, y, 0,
				x + 2 / 3, y, 0,
				x + 2 / 3, y + 1, 0,
				x, y, 0,
				x + 2 / 3, y + 1, 0,
				x, y + 1, 0
			];
			position.set( coordinates, positionSize * vertices * face );
			uv.set( uv1, uvSize * vertices * face );
			var fill = [ face, face, face, face, face, face ];
			faceIndex.set( fill, faceIndexSize * vertices * face );

		}

		var planes = new BufferGeometry();
		planes.setAttribute( 'position', new BufferAttribute( position, positionSize ) );
		planes.setAttribute( 'uv', new BufferAttribute( uv, uvSize ) );
		planes.setAttribute( 'faceIndex', new BufferAttribute( faceIndex, faceIndexSize ) );
		_lodPlanes.push( planes );

		if ( lod > LOD_MIN ) {

			lod --;

		}

	}

	return { _lodPlanes, _sizeLods, _sigmas };

}

function _createRenderTarget( params ) {

	var cubeUVRenderTarget = new WebGLRenderTarget( 3 * SIZE_MAX, 3 * SIZE_MAX, params );
	cubeUVRenderTarget.texture.mapping = CubeUVReflectionMapping;
	cubeUVRenderTarget.texture.name = 'PMREM.cubeUv';
	cubeUVRenderTarget.scissorTest = true;
	return cubeUVRenderTarget;

}

function _setViewport( target, x, y, width, height ) {

	target.viewport.set( x, y, width, height );
	target.scissor.set( x, y, width, height );

}

function _getBlurShader( maxSamples ) {

	var weights = new Float32Array( maxSamples );
	var poleAxis = new Vector3( 0, 1, 0 );
	var shaderMaterial = new RawShaderMaterial( {

		defines: { 'n': maxSamples },

		uniforms: {
			'envMap': { value: null },
			'samples': { value: 1 },
			'weights': { value: weights },
			'latitudinal': { value: false },
			'dTheta': { value: 0 },
			'mipInt': { value: 0 },
			'poleAxis': { value: poleAxis },
			'inputEncoding': { value: ENCODINGS[ LinearEncoding ] },
			'outputEncoding': { value: ENCODINGS[ LinearEncoding ] }
		},

		vertexShader: _getCommonVertexShader(),

		fragmentShader: `
precision mediump float;
precision mediump int;
varying vec3 vOutputDirection;
uniform sampler2D envMap;
uniform int samples;
uniform float weights[n];
uniform bool latitudinal;
uniform float dTheta;
uniform float mipInt;
uniform vec3 poleAxis;

${_getEncodings()}

#define ENVMAP_TYPE_CUBE_UV
#include <cube_uv_reflection_fragment>

vec3 getSample(float theta, vec3 axis) {
	float cosTheta = cos(theta);
	// Rodrigues' axis-angle rotation
	vec3 sampleDirection = vOutputDirection * cosTheta
		+ cross(axis, vOutputDirection) * sin(theta)
		+ axis * dot(axis, vOutputDirection) * (1.0 - cosTheta);
	return bilinearCubeUV(envMap, sampleDirection, mipInt);
}

void main() {
	vec3 axis = latitudinal ? poleAxis : cross(poleAxis, vOutputDirection);
	if (all(equal(axis, vec3(0.0))))
		axis = vec3(vOutputDirection.z, 0.0, - vOutputDirection.x);
	axis = normalize(axis);
	gl_FragColor = vec4(0.0);
	gl_FragColor.rgb += weights[0] * getSample(0.0, axis);
	for (int i = 1; i < n; i++) {
		if (i >= samples)
			break;
		float theta = dTheta * float(i);
		gl_FragColor.rgb += weights[i] * getSample(-1.0 * theta, axis);
		gl_FragColor.rgb += weights[i] * getSample(theta, axis);
	}
	gl_FragColor = linearToOutputTexel(gl_FragColor);
}
		`,

		blending: NoBlending,
		depthTest: false,
		depthWrite: false

	} );

	shaderMaterial.type = 'SphericalGaussianBlur';

	return shaderMaterial;

}

function _getEquirectShader() {

	var texelSize = new Vector2( 1, 1 );
	var shaderMaterial = new RawShaderMaterial( {

		uniforms: {
			'envMap': { value: null },
			'texelSize': { value: texelSize },
			'inputEncoding': { value: ENCODINGS[ LinearEncoding ] },
			'outputEncoding': { value: ENCODINGS[ LinearEncoding ] }
		},

		vertexShader: _getCommonVertexShader(),

		fragmentShader: `
precision mediump float;
precision mediump int;
varying vec3 vOutputDirection;
uniform sampler2D envMap;
uniform vec2 texelSize;

${_getEncodings()}

#define RECIPROCAL_PI 0.31830988618
#define RECIPROCAL_PI2 0.15915494

void main() {
	gl_FragColor = vec4(0.0);
	vec3 outputDirection = normalize(vOutputDirection);
	vec2 uv;
	uv.y = asin(clamp(outputDirection.y, -1.0, 1.0)) * RECIPROCAL_PI + 0.5;
	uv.x = atan(outputDirection.z, outputDirection.x) * RECIPROCAL_PI2 + 0.5;
	vec2 f = fract(uv / texelSize - 0.5);
	uv -= f * texelSize;
	vec3 tl = envMapTexelToLinear(texture2D(envMap, uv)).rgb;
	uv.x += texelSize.x;
	vec3 tr = envMapTexelToLinear(texture2D(envMap, uv)).rgb;
	uv.y += texelSize.y;
	vec3 br = envMapTexelToLinear(texture2D(envMap, uv)).rgb;
	uv.x -= texelSize.x;
	vec3 bl = envMapTexelToLinear(texture2D(envMap, uv)).rgb;
	vec3 tm = mix(tl, tr, f.x);
	vec3 bm = mix(bl, br, f.x);
	gl_FragColor.rgb = mix(tm, bm, f.y);
	gl_FragColor = linearToOutputTexel(gl_FragColor);
}
		`,

		blending: NoBlending,
		depthTest: false,
		depthWrite: false

	} );

	shaderMaterial.type = 'EquirectangularToCubeUV';

	return shaderMaterial;

}

function _getCubemapShader() {

	var shaderMaterial = new RawShaderMaterial( {

		uniforms: {
			'envMap': { value: null },
			'inputEncoding': { value: ENCODINGS[ LinearEncoding ] },
			'outputEncoding': { value: ENCODINGS[ LinearEncoding ] }
		},

		vertexShader: _getCommonVertexShader(),

		fragmentShader: `
precision mediump float;
precision mediump int;
varying vec3 vOutputDirection;
uniform samplerCube envMap;

${_getEncodings()}

void main() {
	gl_FragColor = vec4(0.0);
	gl_FragColor.rgb = envMapTexelToLinear(textureCube(envMap, vec3( - vOutputDirection.x, vOutputDirection.yz ))).rgb;
	gl_FragColor = linearToOutputTexel(gl_FragColor);
}
		`,

		blending: NoBlending,
		depthTest: false,
		depthWrite: false

	} );

	shaderMaterial.type = 'CubemapToCubeUV';

	return shaderMaterial;

}

function _getCommonVertexShader() {

	return `
precision mediump float;
precision mediump int;
attribute vec3 position;
attribute vec2 uv;
attribute float faceIndex;
varying vec3 vOutputDirection;
vec3 getDirection(vec2 uv, float face) {
	uv = 2.0 * uv - 1.0;
	vec3 direction = vec3(uv, 1.0);
	if (face == 0.0) {
		direction = direction.zyx;
		direction.z *= -1.0;
	} else if (face == 1.0) {
		direction = direction.xzy;
		direction.z *= -1.0;
	} else if (face == 3.0) {
		direction = direction.zyx;
		direction.x *= -1.0;
	} else if (face == 4.0) {
		direction = direction.xzy;
		direction.y *= -1.0;
	} else if (face == 5.0) {
		direction.xz *= -1.0;
	}
	return direction;
}
void main() {
	vOutputDirection = getDirection(uv, faceIndex);
	gl_Position = vec4( position, 1.0 );
}
	`;

}

function _getEncodings() {

	return `
uniform int inputEncoding;
uniform int outputEncoding;

#include <encodings_pars_fragment>

vec4 inputTexelToLinear(vec4 value){
	if(inputEncoding == 0){
		return value;
	}else if(inputEncoding == 1){
		return sRGBToLinear(value);
	}else if(inputEncoding == 2){
		return RGBEToLinear(value);
	}else if(inputEncoding == 3){
		return RGBMToLinear(value, 7.0);
	}else if(inputEncoding == 4){
		return RGBMToLinear(value, 16.0);
	}else if(inputEncoding == 5){
		return RGBDToLinear(value, 256.0);
	}else{
		return GammaToLinear(value, 2.2);
	}
}

vec4 linearToOutputTexel(vec4 value){
	if(outputEncoding == 0){
		return value;
	}else if(outputEncoding == 1){
		return LinearTosRGB(value);
	}else if(outputEncoding == 2){
		return LinearToRGBE(value);
	}else if(outputEncoding == 3){
		return LinearToRGBM(value, 7.0);
	}else if(outputEncoding == 4){
		return LinearToRGBM(value, 16.0);
	}else if(outputEncoding == 5){
		return LinearToRGBD(value, 256.0);
	}else{
		return LinearToGamma(value, 2.2);
	}
}

vec4 envMapTexelToLinear(vec4 color) {
	return inputTexelToLinear(color);
}
	`;

}

export { PMREMGenerator };