opengl-PBR基于物理的渲染(Physically Based Rendering)：光照实际渲染器

顶点着色器

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec2 aTexCoords;
layout (location = 2) in vec3 aNormal;

out vec2 TexCoords;
out vec3 WorldPos;
out vec3 Normal;

uniform mat4 projection;
uniform mat4 view;
uniform mat4 model;

void main()
{
    TexCoords = aTexCoords;
    WorldPos = vec3(model * vec4(aPos, 1.0));
    Normal = mat3(model) * aNormal;   

    gl_Position =  projection * view * vec4(WorldPos, 1.0);
}

片段着色器

#version 330 core
out vec4 FragColor;
in vec2 TexCoords;
in vec3 WorldPos;
in vec3 Normal;

// material parameters
uniform sampler2D albedoMap;
uniform sampler2D normalMap;
uniform sampler2D metallicMap;
uniform sampler2D roughnessMap;
uniform sampler2D aoMap;

// lights
uniform vec3 lightPositions[4];
uniform vec3 lightColors[4];

uniform vec3 camPos;

const float PI = 3.14159265359;
// ----------------------------------------------------------------------------
// Easy trick to get tangent-normals to world-space to keep PBR code simplified.
// Don't worry if you don't get what's going on; you generally want to do normal 
// mapping the usual way for performance anways; I do plan make a note of this 
// technique somewhere later in the normal mapping tutorial.
vec3 getNormalFromMap()
{
    vec3 tangentNormal = texture(normalMap, TexCoords).xyz * 2.0 - 1.0;

    vec3 Q1  = dFdx(WorldPos);
    vec3 Q2  = dFdy(WorldPos);
    vec2 st1 = dFdx(TexCoords);
    vec2 st2 = dFdy(TexCoords);

    vec3 N   = normalize(Normal);
    vec3 T  = normalize(Q1*st2.t - Q2*st1.t);
    vec3 B  = -normalize(cross(N, T));
    mat3 TBN = mat3(T, B, N);

    return normalize(TBN * tangentNormal);
}
// ----------------------------------------------------------------------------
float DistributionGGX(vec3 N, vec3 H, float roughness)
{
    float a = roughness*roughness;
    float a2 = a*a;
    float NdotH = max(dot(N, H), 0.0);
    float NdotH2 = NdotH*NdotH;

    float nom   = a2;
    float denom = (NdotH2 * (a2 - 1.0) + 1.0);
    denom = PI * denom * denom;

    return nom / denom;
}
// ----------------------------------------------------------------------------
float GeometrySchlickGGX(float NdotV, float roughness)
{
    float r = (roughness + 1.0);
    float k = (r*r) / 8.0;

    float nom   = NdotV;
    float denom = NdotV * (1.0 - k) + k;

    return nom / denom;
}
// 需要将观察方向（几何遮蔽(Geometry Obstruction)）和光线方向向量（几何阴影(Geometry Shadowing)）都考虑进去。
// 我们可以使用史密斯法(Smith’s method)来把两者都纳入其中----------------------------------------------------------------------------
float GeometrySmith(vec3 N, vec3 V, vec3 L, float roughness)
{
    float NdotV = max(dot(N, V), 0.0);
    float NdotL = max(dot(N, L), 0.0);
    float ggx2 = GeometrySchlickGGX(NdotV, roughness);
    float ggx1 = GeometrySchlickGGX(NdotL, roughness);

    return ggx1 * ggx2;
}
// 菲涅尔方程----------------------------------------------------------------------------
vec3 fresnelSchlick(float cosTheta, vec3 F0)
{
    return F0 + (1.0 - F0) * pow(max(1.0 - cosTheta, 0.0), 5.0);
}
// ----------------------------------------------------------------------------
void main()
{		
    vec3 albedo     = pow(texture(albedoMap, TexCoords).rgb, vec3(2.2));
    float metallic  = texture(metallicMap, TexCoords).r;
    float roughness = texture(roughnessMap, TexCoords).r;
    float ao        = texture(aoMap, TexCoords).r;

    vec3 N = getNormalFromMap();
    vec3 V = normalize(camPos - WorldPos);

    // calculate reflectance at normal incidence; if dia-electric (like plastic) use F0 
    // of 0.04 and if it's a metal, use the albedo color as F0 (metallic workflow)    
    vec3 F0 = vec3(0.04); 
    F0 = mix(F0, albedo, metallic);

    // reflectance equation
    vec3 Lo = vec3(0.0);
    for(int i = 0; i < 4; ++i) 
    {
        // calculate per-light radiance
        vec3 L = normalize(lightPositions[i] - WorldPos);
        vec3 H = normalize(V + L);
        float distance = length(lightPositions[i] - WorldPos);
        float attenuation = 1.0 / (distance * distance);
        vec3 radiance = lightColors[i] * attenuation;

        // Cook-Torrance BRDF
        float NDF = DistributionGGX(N, H, roughness);   
        float G   = GeometrySmith(N, V, L, roughness);      
        vec3 F    = fresnelSchlick(max(dot(H, V), 0.0), F0);
           
        vec3 numerator    = NDF * G * F; 
        float denominator = 4 * max(dot(N, V), 0.0) * max(dot(N, L), 0.0) + 0.001; // 0.001 to prevent divide by zero.
        vec3 specular = numerator / denominator;
        
        // kS is equal to Fresnel
        vec3 kS = F;
        // for energy conservation, the diffuse and specular light can't
        // be above 1.0 (unless the surface emits light); to preserve this
        // relationship the diffuse component (kD) should equal 1.0 - kS.
        vec3 kD = vec3(1.0) - kS;
        // multiply kD by the inverse metalness such that only non-metals 
        // have diffuse lighting, or a linear blend if partly metal (pure metals
        // have no diffuse light).
        kD *= 1.0 - metallic;	  

        // scale light by NdotL
        float NdotL = max(dot(N, L), 0.0);        

        // add to outgoing radiance Lo
        Lo += (kD * albedo / PI + specular) * radiance * NdotL;  // note that we already multiplied the BRDF by the Fresnel (kS) so we won't multiply by kS again
    }   
    
    // ambient lighting (note that the next IBL tutorial will replace 
    // this ambient lighting with environment lighting).
    vec3 ambient = vec3(0.03) * albedo * ao;
    
    vec3 color = ambient + Lo;

    // HDR tonemapping
    color = color / (color + vec3(1.0));
    // gamma correct
    color = pow(color, vec3(1.0/2.2)); 

    FragColor = vec4(color, 1.0);
}

主函数

    // build and compile shaders
    // -------------------------
    Shader shader("1.2.pbr.vert", "1.2.pbr.frag");

    shader.use();
    shader.setInt("albedoMap", 0);
    shader.setInt("normalMap", 1);
    shader.setInt("metallicMap", 2);
    shader.setInt("roughnessMap", 3);
    shader.setInt("aoMap", 4);

    // load PBR material textures
    // --------------------------
    unsigned int albedo = loadTexture("resources/textures/pbr/rusted_iron/albedo.png");
    unsigned int normal = loadTexture("resources/textures/pbr/rusted_iron/normal.png");
    unsigned int metallic = loadTexture("resources/textures/pbr/rusted_iron/metallic.png");
    unsigned int roughness = loadTexture("resources/textures/pbr/rusted_iron/roughness.png");
    unsigned int ao = loadTexture("resources/textures/pbr/rusted_iron/ao.png");

    // lights
    // ------
    glm::vec3 lightPositions[] = {
        glm::vec3(0.0f, 0.0f, 10.0f),
    };
    glm::vec3 lightColors[] = {
        glm::vec3(150.0f, 150.0f, 150.0f),
    };
    //球体数量
    int nrRows = 7;
    int nrColumns = 7;
    float spacing = 2.5;

    // initialize static shader uniforms before rendering
    // --------------------------------------------------
    glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f);
    shader.use();
    shader.setMat4("projection", projection);

    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // per-frame time logic
        // --------------------
        float currentFrame = glfwGetTime();
        deltaTime = currentFrame - lastFrame;
        lastFrame = currentFrame;

        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        shader.use();
        glm::mat4 view = camera.GetViewMatrix();
        shader.setMat4("view", view);
        shader.setVec3("camPos", camera.Position);
        //绑定纹理图片
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, albedo);
        glActiveTexture(GL_TEXTURE1);
        glBindTexture(GL_TEXTURE_2D, normal);
        glActiveTexture(GL_TEXTURE2);
        glBindTexture(GL_TEXTURE_2D, metallic);
        glActiveTexture(GL_TEXTURE3);
        glBindTexture(GL_TEXTURE_2D, roughness);
        glActiveTexture(GL_TEXTURE4);
        glBindTexture(GL_TEXTURE_2D, ao);

        // render rows*column number of spheres with material properties defined by textures (they all have the same material properties)
        //按照球体数量的行和列来渲染球体
        glm::mat4 model = glm::mat4(1.0f);
        for (int row = 0; row < nrRows; ++row)
        {
            for (int col = 0; col < nrColumns; ++col)
            {
                model = glm::mat4(1.0f);
                model = glm::translate(model, glm::vec3(
                    (float)(col - (nrColumns / 2)) * spacing,
                    (float)(row - (nrRows / 2)) * spacing,
                    0.0f
                ));
                shader.setMat4("model", model);
                renderSphere();//开始渲染
            }
        }

        // render light source (simply re-render sphere at light positions)
        // this looks a bit off as we use the same shader, but it'll make their positions obvious and 
        // keeps the codeprint small.
        //在光源出再渲染一个普通的球体
        for (unsigned int i = 0; i < sizeof(lightPositions) / sizeof(lightPositions[0]); ++i)
        {
            glm::vec3 newPos = lightPositions[i] + glm::vec3(sin(glfwGetTime() * 5.0) * 5.0, 0.0, 0.0);
            newPos = lightPositions[i];
            shader.setVec3("lightPositions[" + std::to_string(i) + "]", newPos);
            shader.setVec3("lightColors[" + std::to_string(i) + "]", lightColors[i]);

            model = glm::mat4(1.0f);
            model = glm::translate(model, newPos);
            model = glm::scale(model, glm::vec3(0.5f));
            shader.setMat4("model", model);
            renderSphere();
        }

        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }