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( function () {
/**
* 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://simonwallner.at/project/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
*/
class Sky extends THREE.Mesh {
constructor() {
const shader = Sky.SkyShader;
const material = new THREE.ShaderMaterial( {
name: 'SkyShader',
fragmentShader: shader.fragmentShader,
vertexShader: shader.vertexShader,
uniforms: THREE.UniformsUtils.clone( shader.uniforms ),
side: THREE.BackSide,
depthWrite: false
} );
super( new THREE.BoxGeometry( 1, 1, 1 ), material );
this.isSky = true;
}
}
Sky.SkyShader = {
uniforms: {
'turbidity': {
value: 2
},
'rayleigh': {
value: 1
},
'mieCoefficient': {
value: 0.005
},
'mieDirectionalG': {
value: 0.8
},
'sunPosition': {
value: new THREE.Vector3()
},
'up': {
value: new THREE.Vector3( 0, 1, 0 )
}
},
vertexShader: /* glsl */`
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;
}`,
fragmentShader: /* glsl */`
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>
}`
};
THREE.Sky = Sky;
} )();