[three.js][typescript] - Shader

THREE.JS도 WEBGL 기반이기 때문에 Shader(GLSL)등을 활용할 수 있다.

 

눈이 온다던지 파도 물결을 표현한다던지 할 때 후처리(Post-Processing) 작업을 할 때 많이 사용한다.

 

 

 

 

TMI) 내가 일하는 곳에서는 보통 정점 쉐이더와 프래그먼트 쉐이더를 사용하는 것 같다.

 

 

 

 

 

 

다음의 사이트를 참고하여 학습하였다.

 

three.js docs

 

기존에 학습하던 모델에 Shader 기반의 코드를 올려보았다.

 

 

 

 

 

위와 같이 태양의 포지션과 그로 인해 발생하는 광원들을 확인할 수 있다.

 

그래서 이게 왜 쉐이더냐??

 

 

 

 

 

사실 추가한 코드는 위의 10줄이 전부이다만

 

해당 Sky 클래스를 import하는 애드온의 코드를 확인해볼 필요가 있다.

 

 

 

 

 

 

 

three.js/examples/jsm/objects/Sky.js at master · mrdoob/three.js

 

import {
    BackSide,
    BoxGeometry,
    Mesh,
    ShaderMaterial,
    UniformsUtils,
    Vector3
} from 'three';
 
/**
 * Represents a skydome for scene backgrounds. Based on [A Practical Analytic Model for Daylight]{@link https://www.researchgate.net/publication/220720443_A_Practical_Analytic_Model_for_Daylight}
 * aka The Preetham Model, the de facto standard for analytical skydomes.
 *
 * Note that this class can only be used with {@link WebGLRenderer}.
 * When using {@link WebGPURenderer}, use {@link SkyMesh}.
 *
 * More references:
 *
 * - {@link http://simonwallner.at/project/atmospheric-scattering/}
 * - {@link http://blenderartists.org/forum/showthread.php?245954-preethams-sky-impementation-HDR}
 *
 *
 * ```js
 * const sky = new Sky();
 * sky.scale.setScalar( 10000 );
 * scene.add( sky );
 * ```
 *
 * @augments Mesh
*/
class Sky extends Mesh {
 
    /**
     * Constructs a new skydome.
     */
    constructor() {
 
        const shader = Sky.SkyShader;
 
        const material = new ShaderMaterial( {
            name: shader.name,
            uniforms: UniformsUtils.clone( shader.uniforms ),
            vertexShader: shader.vertexShader,
            fragmentShader: shader.fragmentShader,
            side: BackSide,
            depthWrite: false
        } );
 
        super( new BoxGeometry( 1, 1, 1 ), material );
 
        /**
         * This flag can be used for type testing.
         *
         * @type {boolean}
         * @readonly
         * @default true
         */
        this.isSky = true;
 
    }
 
}
 
Sky.SkyShader = {
 
    name: '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: /* 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-calculation 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 (absorption + 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;
 
        // 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 - cameraPosition );
 
            // 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 <colorspace_fragment>
 
        }`
 
};
 
export { Sky };

 

위 코드와 같이 버텍스 쉐이더와 프레그먼트 쉐이더로 샘플링 하였다.

 

벡터의 값을 다루다보니 clamp로 값을 제한할 때 코사인, 사인 등의 삼각함수를 많이 사용하는 것을 확인할 수 있다.

 

원시적인 shader값을 수정하여 원하는 디테일을 표현하기 위해서는 수학적 지식이 많이 필요한 것 같다.