three.js/examples/js/objects/Sky.js

( 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://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
*/

	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 );

		}

	}

	Sky.prototype.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: [ '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' )
	};

	THREE.Sky = Sky;

} )();