ThreeJS 物理材质shader源码分析(像素着色器)

像素着色器(meshphysical_frag.glsl)

#define PHYSICAL

uniform vec3 diffuse; // 漫反射颜色

uniform vec3 emissive; // 自发光颜色

uniform float roughness; // 粗糙度

uniform float metalness; // 金属性

uniform float opacity;  // 透明度

#ifndef STANDARD

uniform float clearCoat;  //

uniform float clearCoatRoughness;

#endif

varying vec3 vViewPosition; // 摄像机空间的坐标

#ifndef FLAT_SHADED

varying vec3 vNormal; // 摄像机空间的法线

#endif

#include <common>           //  包含着色器公共模块(包含常用的数学工具函数以及一些常量定义什么的)

#include <packing>          // 数据编码解码功能函数

#include <dithering_pars_fragment>  // 抖动处理的定义

#include <color_pars_fragment>      // 颜色处理的定义

#include <uv_pars_fragment>         // uv相关处理的定义

#include <uv2_pars_fragment>        // uv2相关处理的定义

#include <map_pars_fragment>        // map贴图相关处理的定义

#include <alphamap_pars_fragment>   // alphamap贴图的处理定义

#include <aomap_pars_fragment>      // aomap贴图的处理定义

#include <lightmap_pars_fragment>   // lighmap贴图处理定义

#include <emissivemap_pars_fragment>    // emissivemap贴图处理的定义

#include <envmap_pars_fragment> // envmap贴图处理的定义

#include <fog_pars_fragment>    // 雾化需要的定义

#include <bsdfs>                    // brdf相关的功能函数

#include <cube_uv_reflection_fragment>  // cubemap反射相关

#include <lights_pars_begin>        // 灯光相关定义

#include <lights_pars_maps>         // 灯光贴图相关

#include <lights_physical_pars_fragment> // 灯光相关物理运算

#include <shadowmap_pars_fragment>  // shadowmap影子相关运算定义

#include <bumpmap_pars_fragment>        // bumpmap相关运算的定义

#include <normalmap_pars_fragment>      // normalmap相关运算的定义

#include <roughnessmap_pars_fragment>       // roughnessmap相关运算的定义

#include <metalnessmap_pars_fragment>       // metalnessmap相关运算的定义

#include <logdepthbuf_pars_fragment>        // logdepth相关运算的定义

#include <clipping_planes_pars_fragment>        // clipplane裁剪平面相关的定义

void main() {

#include <clipping_planes_fragment> // 裁剪平面裁剪

vec4 diffuseColor = vec4( diffuse, opacity );// 合成rgba四通道漫反射颜色

ReflectedLight reflectedLight = ReflectedLight( vec3( 0.0 ), vec3( 0.0 ), vec3( 0.0 ), vec3( 0.0 ) );

vec3 totalEmissiveRadiance = emissive;

#include <logdepthbuf_fragment> // logdepth运算

#include <map_fragment>         // map通道颜色采样

#include <color_fragment>       // color参与计算

#include <alphamap_fragment>    // alphamap通道颜色采样

#include <alphatest_fragment>   // alpha测试

#include <roughnessmap_fragment>    // 粗糙贴图采样

#include <metalnessmap_fragment>    // 金属性贴图采样

#include <normal_fragment_begin>    // 法线贴图基本运算

#include <normal_fragment_maps>     // 法线通过法线贴图运算

#include <emissivemap_fragment>     // 自发光贴图采样

// accumulation

#include <lights_physical_fragment> // 物理光照基础运算

#include <lights_fragment_begin> // 计算各种灯光入射光和反射光信息

#include <lights_fragment_maps> // 从环境光和光照贴图获取辐射

#include <lights_fragment_end>  // 根据辐射光取得反射信息

// modulation

#include <aomap_fragment>   // 根据AO贴图调整反射光照强度

// 反射光直接漫反射+间接漫反射+直接高光+间接高光+自发光 = 输出光照颜色

vec3 outgoingLight = reflectedLight.directDiffuse + reflectedLight.indirectDiffuse + reflectedLight.directSpecular + reflectedLight.indirectSpecular + totalEmissiveRadiance;

gl_FragColor = vec4( outgoingLight, diffuseColor.a );

#include <tonemapping_fragment>// tonemap进行曝光

#include <encodings_fragment> // 颜色编码

#include <fog_fragment>             // 雾化颜色运算

#include <premultiplied_alpha_fragment> // 颜色预乘alpha

#include <dithering_fragment>   // 颜色随机抖动

}

我将这个fragmentshader提取了关于物理材质着色的核心算法方便理解代码如下:

核心算法只包含直接照明产生的漫反射颜色和高光颜色,直接照明只计算了点光源(没有计算距离衰减),去掉了各种贴图采样数据以最简化shader代码

// 由vertexshader传递过来的法线,位置,uv
varying vec3 vNormal;
varying vec3 vPosition;
varying vec2 vUv;

// 材质参数
uniform vec3  diffuse;    //  漫反射
uniform float metallic;  // 金属性
uniform float roughness;    // 粗糙度

#if NUM_POINT_LIGHTS > 0
// 点光源信息
struct PointLight {
        vec3 position;
        vec3 color;
        float distance;
        float decay;
};
uniform PointLight pointLights[ NUM_POINT_LIGHTS ];
#endif
#if NUM_DIR_LIGHTS > 0
    struct DirectionalLight {
        vec3 direction;
        vec3 color;
    };
    uniform DirectionalLight directionalLights[ NUM_DIR_LIGHTS ];
#endif
float pow2( const in float x ) { return x*x; }
const float PI = 3.14159265359;
#define EPSILON 1e-6
#define MAXIMUM_SPECULAR_COEFFICIENT 0.16
#define DEFAULT_SPECULAR_COEFFICIENT 0.04
#define RECIPROCAL_PI 0.31830988618
// 光照反射信息（直接光的漫反射和高光色)
struct ReflectedLight {
    vec3 directDiffuse;
    vec3 directSpecular;
    vec3 indirectDiffuse;
};
// 入射光照信息(颜色和方向)
struct IncidentLight {
    vec3 color;
    vec3 direction;
};
// 几何信息(位置，法线，视角方向)
struct GeometricContext {
    vec3 position;
    vec3 normal;
    vec3 viewDir;
};
// 物理材质信息
struct PhysicalMaterial {
    vec3    diffuseColor;
    float    specularRoughness;
    vec3    specularColor;
};

vec3 F_Schlick( const in vec3 specularColor, const in float dotLH ) {
    float fresnel = exp2( ( -5.55473 * dotLH - 6.98316 ) * dotLH );
    return ( 1.0 - specularColor ) * fresnel + specularColor;
}
float G_GGX_SmithCorrelated( const in float alpha, const in float dotNL, const in float dotNV ) {
    float a2 = pow2( alpha );
    float gv = dotNL * sqrt( a2 + ( 1.0 - a2 ) * pow2( dotNV ) );
    float gl = dotNV * sqrt( a2 + ( 1.0 - a2 ) * pow2( dotNL ) );
    return 0.5 / max( gv + gl, EPSILON );
}
float D_GGX( const in float alpha, const in float dotNH ) {
    float a2 = pow2( alpha );
    float denom = pow2( dotNH ) * ( a2 - 1.0 ) + 1.0;
    return RECIPROCAL_PI * a2 / pow2( denom );
}
vec3 BRDF_Specular_GGX_Environment( const in GeometricContext geometry, const in vec3 specularColor, const in float roughness ) {
    float dotNV = saturate( dot( geometry.normal, geometry.viewDir ) );
    const vec4 c0 = vec4( - , - 0.0275, - 0.572, 0.022 );
    const vec4 c1 = vec4( , 0.0425, 1.04, - 0.04 );
    vec4 r = roughness * c0 + c1;
    float a004 = min( r.x * r.x, exp2( - 9.28 * dotNV ) ) * r.x + r.y;
    vec2 AB = vec2( -1.04, 1.04 ) * a004 + r.zw;
    return specularColor * AB.x + AB.y;
}
vec3 BRDF_Specular_GGX( in GeometricContext geometry, in IncidentLight directLight,const in vec3 specularColor, const in float roughness) {
    float alpha = pow2( roughness );
    vec3 halfDir = normalize( directLight.direction + geometry.viewDir );
    float dotNL = saturate( dot( geometry.normal, directLight.direction ) );
    float dotNV = saturate( dot( geometry.normal, geometry.viewDir ) );
    float dotNH = saturate( dot( geometry.normal, halfDir ) );
    float dotLH = saturate( dot( directLight.direction, halfDir ) );
    vec3  F = F_Schlick( specularColor, dotLH );
    float G = G_GGX_SmithCorrelated( alpha, dotNL, dotNV );
    float D = D_GGX( alpha, dotNH );
    return F * ( G * D );
}
vec3 BRDF_Diffuse_Lambert( const in vec3 diffuseColor ) {
    return RECIPROCAL_PI * diffuseColor;
}
float clearCoatDHRApprox( const in float roughness, const in float dotNL ) {
    return DEFAULT_SPECULAR_COEFFICIENT + ( 1.0 - DEFAULT_SPECULAR_COEFFICIENT ) * ( pow( 1.0 - dotNL, 5.0 ) * pow( 1.0 - roughness, 2.0 ) );
}
void RE_Direct_Physical(in GeometricContext geometry,in PhysicalMaterial material, in IncidentLight directLight,inout ReflectedLight reflectedLight ) {

    float dotNL = saturate( dot( geometry.normal,directLight.direction ) );// lambert漫反射因子
    vec3 irradiance = dotNL * directLight.color; // 辐射
    irradiance *= PI; // * PI 

    reflectedLight.directDiffuse += irradiance * BRDF_Diffuse_Lambert( material.diffuseColor );
    // 重点就是这里了,高光算法和blinn-phong差距巨大
    reflectedLight.directSpecular += irradiance * BRDF_Specular_GGX( geometry,directLight,material.specularColor,material.specularRoughness);

}
void RE_IndirectDiffuse_Physical( const in vec3 irradiance, const in GeometricContext geometry, const in PhysicalMaterial material, inout ReflectedLight reflectedLight ) {
    reflectedLight.indirectDiffuse += irradiance * BRDF_Diffuse_Lambert( material.diffuseColor );
}
vec3 getAmbientLightIrradiance( const in vec3 ambientLightColor ) {
    vec3 irradiance = ambientLightColor;
    irradiance *= PI;
    return irradiance;
}
#define RE_IndirectDiffuse        RE_IndirectDiffuse_Physical
void main() {
    // 存放几何数据
    GeometricContext geometry;
    geometry.position = vPosition;
    geometry.normal = normalize(vNormal);
    geometry.viewDir = normalize(-vPosition); // 因为是相机空间只需要对位置坐标取反0-vPosition
    // 存放物理材质信息
    PhysicalMaterial material;
    material.diffuseColor = diffuse * ( 1.0 - metallic );    // 金属性越强漫反射颜色越小
    material.specularRoughness = clamp( roughness, 0.04, 1.0 );    // 粗燥度
    material.specularColor = mix( vec3( DEFAULT_SPECULAR_COEFFICIENT ), diffuse.rgb, metallic ); // 这里做了个mix 金属性为0高光颜色也不至于是黑色

    // 初始化光照反射
    ReflectedLight reflectedLight = ReflectedLight( vec3( 0.0 ), vec3( 0.0 ),vec3(0.0) ); 

    IncidentLight directLight;// 直接入射光照
#if NUM_POINT_LIGHTS > 0
    for(int i = ; i < NUM_POINT_LIGHTS; ++i)
    {
        directLight.color = pointLights[i].color;    // 入射光颜色
        directLight.direction =  normalize(pointLights[i].position - vPosition);    // 入射光的方向
        RE_Direct_Physical(geometry,material,directLight,reflectedLight);    // 计算直接光产生的反射光信息
    }
#endif
#if NUM_DIR_LIGHTS > 0
    for(int i = ; i < NUM_DIR_LIGHTS; ++i)
    {
        directLight.color = directionalLights[i].color;    // 入射光颜色
        directLight.direction = directionalLights[i].direction;
        RE_Direct_Physical(geometry,material,directLight,reflectedLight);    // 计算直接光产生的反射光信息
    }
#endif

    vec3 irradiance = getAmbientLightIrradiance( vec3(0.13) );
    RE_IndirectDiffuse( irradiance, geometry, material, reflectedLight );
    // 反射光信息加合为最后颜色
    vec3 color =  reflectedLight.directDiffuse + reflectedLight.directSpecular+reflectedLight.indirectDiffuse;

    // HDR tonemapping
    color = saturate(color/(color+vec3(1.0)));
    // gamma correct
    color = pow(color, vec3(1.0/2.0)); 

    gl_FragColor =  vec4(color, 1.0);
}

下面是一个点光源和一个方向光的效果（从左到右粗糙度加强，从下到上金属性加强):