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