text: /// <reference types="./Sky.d.ts" />
  /// <reference lib="dom" />
  import {
    BackSide,
    BoxBufferGeometry,
    Mesh,
    ShaderMaterial,
    UniformsUtils,
    Vector3,
  } from "../../../src/Three.js";
  /**
   * Based on "A Practical Analytic Model for Daylight"
   * aka The Preetham Model, the de facto standard analytic skydome model
   * https://www.researchgate.net/publication/220720443_A_Practical_Analytic_Model_for_Daylight
   *
   * First implemented by Simon Wallner
   * http://www.simonwallner.at/projects/atmospheric-scattering
   *
   * Improved by Martin Upitis
   * http://blenderartists.org/forum/showthread.php?245954-preethams-sky-impementation-HDR
   *
   * Three.js integration by zz85 http://twitter.com/blurspline
  */
  
  var Sky = function () {
    var shader = Sky.SkyShader;
  
    var material = new ShaderMaterial({
      name: "SkyShader",
      fragmentShader: shader.fragmentShader,
      vertexShader: shader.vertexShader,
      uniforms: UniformsUtils.clone(shader.uniforms),
      side: BackSide,
      depthWrite: false,
    });
  
    Mesh.call(this, new BoxBufferGeometry(1, 1, 1), material);
  };
  
  Sky.prototype = Object.create(Mesh.prototype);
  
  Sky.SkyShader = {
    uniforms: {
      "turbidity": { value: 2 },
      "rayleigh": { value: 1 },
      "mieCoefficient": { value: 0.005 },
      "mieDirectionalG": { value: 0.8 },
      "sunPosition": { value: new Vector3() },
      "up": { value: new Vector3(0, 1, 0) },
    },
  
    vertexShader: [
      "uniform vec3 sunPosition;",
      "uniform float rayleigh;",
      "uniform float turbidity;",
      "uniform float mieCoefficient;",
      "uniform vec3 up;",
  
      "varying vec3 vWorldPosition;",
      "varying vec3 vSunDirection;",
      "varying float vSunfade;",
      "varying vec3 vBetaR;",
      "varying vec3 vBetaM;",
      "varying float vSunE;",
  
      // constants for atmospheric scattering
      "const float e = 2.71828182845904523536028747135266249775724709369995957;",
      "const float pi = 3.141592653589793238462643383279502884197169;",
  
      // wavelength of used primaries, according to preetham
      "const vec3 lambda = vec3( 680E-9, 550E-9, 450E-9 );",
      // this pre-calcuation replaces older TotalRayleigh(vec3 lambda) function:
      // (8.0 * pow(pi, 3.0) * pow(pow(n, 2.0) - 1.0, 2.0) * (6.0 + 3.0 * pn)) / (3.0 * N * pow(lambda, vec3(4.0)) * (6.0 - 7.0 * pn))
      "const vec3 totalRayleigh = vec3( 5.804542996261093E-6, 1.3562911419845635E-5, 3.0265902468824876E-5 );",
  
      // mie stuff
      // K coefficient for the primaries
      "const float v = 4.0;",
      "const vec3 K = vec3( 0.686, 0.678, 0.666 );",
      // MieConst = pi * pow( ( 2.0 * pi ) / lambda, vec3( v - 2.0 ) ) * K
      "const vec3 MieConst = vec3( 1.8399918514433978E14, 2.7798023919660528E14, 4.0790479543861094E14 );",
  
      // earth shadow hack
      // cutoffAngle = pi / 1.95;
      "const float cutoffAngle = 1.6110731556870734;",
      "const float steepness = 1.5;",
      "const float EE = 1000.0;",
  
      "float sunIntensity( float zenithAngleCos ) {",
      "	zenithAngleCos = clamp( zenithAngleCos, -1.0, 1.0 );",
      "	return EE * max( 0.0, 1.0 - pow( e, -( ( cutoffAngle - acos( zenithAngleCos ) ) / steepness ) ) );",
      "}",
  
      "vec3 totalMie( float T ) {",
      "	float c = ( 0.2 * T ) * 10E-18;",
      "	return 0.434 * c * MieConst;",
      "}",
  
      "void main() {",
  
      "	vec4 worldPosition = modelMatrix * vec4( position, 1.0 );",
      "	vWorldPosition = worldPosition.xyz;",
  
      "	gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );",
      "	gl_Position.z = gl_Position.w;", // set z to camera.far
  
      "	vSunDirection = normalize( sunPosition );",
  
      "	vSunE = sunIntensity( dot( vSunDirection, up ) );",
  
      "	vSunfade = 1.0 - clamp( 1.0 - exp( ( sunPosition.y / 450000.0 ) ), 0.0, 1.0 );",
  
      "	float rayleighCoefficient = rayleigh - ( 1.0 * ( 1.0 - vSunfade ) );",
  
      // extinction (absorbtion + out scattering)
      // rayleigh coefficients
      "	vBetaR = totalRayleigh * rayleighCoefficient;",
  
      // mie coefficients
      "	vBetaM = totalMie( turbidity ) * mieCoefficient;",
  
      "}",
    ].join("\n"),
  
    fragmentShader: [
      "varying vec3 vWorldPosition;",
      "varying vec3 vSunDirection;",
      "varying float vSunfade;",
      "varying vec3 vBetaR;",
      "varying vec3 vBetaM;",
      "varying float vSunE;",
  
      "uniform float mieDirectionalG;",
      "uniform vec3 up;",
  
      "const vec3 cameraPos = vec3( 0.0, 0.0, 0.0 );",
  
      // constants for atmospheric scattering
      "const float pi = 3.141592653589793238462643383279502884197169;",
  
      "const float n = 1.0003;", // refractive index of air
      "const float N = 2.545E25;", // number of molecules per unit volume for air at 288.15K and 1013mb (sea level -45 celsius)
  
      // optical length at zenith for molecules
      "const float rayleighZenithLength = 8.4E3;",
      "const float mieZenithLength = 1.25E3;",
      // 66 arc seconds -> degrees, and the cosine of that
      "const float sunAngularDiameterCos = 0.999956676946448443553574619906976478926848692873900859324;",
  
      // 3.0 / ( 16.0 * pi )
      "const float THREE_OVER_SIXTEENPI = 0.05968310365946075;",
      // 1.0 / ( 4.0 * pi )
      "const float ONE_OVER_FOURPI = 0.07957747154594767;",
  
      "float rayleighPhase( float cosTheta ) {",
      "	return THREE_OVER_SIXTEENPI * ( 1.0 + pow( cosTheta, 2.0 ) );",
      "}",
  
      "float hgPhase( float cosTheta, float g ) {",
      "	float g2 = pow( g, 2.0 );",
      "	float inverse = 1.0 / pow( 1.0 - 2.0 * g * cosTheta + g2, 1.5 );",
      "	return ONE_OVER_FOURPI * ( ( 1.0 - g2 ) * inverse );",
      "}",
  
      "void main() {",
  
      "	vec3 direction = normalize( vWorldPosition - cameraPos );",
  
      // optical length
      // cutoff angle at 90 to avoid singularity in next formula.
      "	float zenithAngle = acos( max( 0.0, dot( up, direction ) ) );",
      "	float inverse = 1.0 / ( cos( zenithAngle ) + 0.15 * pow( 93.885 - ( ( zenithAngle * 180.0 ) / pi ), -1.253 ) );",
      "	float sR = rayleighZenithLength * inverse;",
      "	float sM = mieZenithLength * inverse;",
  
      // combined extinction factor
      "	vec3 Fex = exp( -( vBetaR * sR + vBetaM * sM ) );",
  
      // in scattering
      "	float cosTheta = dot( direction, vSunDirection );",
  
      "	float rPhase = rayleighPhase( cosTheta * 0.5 + 0.5 );",
      "	vec3 betaRTheta = vBetaR * rPhase;",
  
      "	float mPhase = hgPhase( cosTheta, mieDirectionalG );",
      "	vec3 betaMTheta = vBetaM * mPhase;",
  
      "	vec3 Lin = pow( vSunE * ( ( betaRTheta + betaMTheta ) / ( vBetaR + vBetaM ) ) * ( 1.0 - Fex ), vec3( 1.5 ) );",
      "	Lin *= mix( vec3( 1.0 ), pow( vSunE * ( ( betaRTheta + betaMTheta ) / ( vBetaR + vBetaM ) ) * Fex, vec3( 1.0 / 2.0 ) ), clamp( pow( 1.0 - dot( up, vSunDirection ), 5.0 ), 0.0, 1.0 ) );",
  
      // nightsky
      "	float theta = acos( direction.y ); // elevation --> y-axis, [-pi/2, pi/2]",
      "	float phi = atan( direction.z, direction.x ); // azimuth --> x-axis [-pi/2, pi/2]",
      "	vec2 uv = vec2( phi, theta ) / vec2( 2.0 * pi, pi ) + vec2( 0.5, 0.0 );",
      "	vec3 L0 = vec3( 0.1 ) * Fex;",
  
      // composition + solar disc
      "	float sundisk = smoothstep( sunAngularDiameterCos, sunAngularDiameterCos + 0.00002, cosTheta );",
      "	L0 += ( vSunE * 19000.0 * Fex ) * sundisk;",
  
      "	vec3 texColor = ( Lin + L0 ) * 0.04 + vec3( 0.0, 0.0003, 0.00075 );",
  
      "	vec3 retColor = pow( texColor, vec3( 1.0 / ( 1.2 + ( 1.2 * vSunfade ) ) ) );",
  
      "	gl_FragColor = vec4( retColor, 1.0 );",
  
      "#include <tonemapping_fragment>",
      "#include <encodings_fragment>",
  
      "}",
    ].join("\n"),
  };
  
  export { Sky };
  