25.opengl高级光照-Gamma校正

公号sumsmile

发布于 2020-07-15 16:12:46

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发布于 2020-07-15 16:12:46

文章被收录于专栏：音视频技术学习笔记音视频技术学习笔记

本章学习之前，先复习基础光照和材质的内容，光照的基础知识有些遗忘了，温故知新。

一、原理介绍

简单理解：人对光强度的感知是非线性的。亮度的范围如果是[0,1]，0是黑色，1是纯白色，那么0.5应该代表的是中间灰色吗？NO!!人能感知到的中间灰度值是亮度为0.2左右的光强。

这也符合人的正常感觉，人对光强逐步增加的初期感知非常强烈，好比，饥饿的人吃10个饼，并不是吃到第5、6个饼时饥饿感减少一半，是头几个饼吃充饥感最强。

既然人感觉到的中间亮度是0.2的光强，为了最大化利用内存，模拟人的感知特点，把0.2的光强设为中间值，用一半的颜色内存存放0到0.2中间的亮度。照相机实际上就是这么做的。而我们常规的显示器在解码颜色时，也会把经过处理后的颜色再还原回去，显示器默认颜色是经过非线性处理的。

为了适配显示器的对颜色的还原，纹理在渲染过程中就要做gamma校正。现在的显示器也可以自己设置gamma值。

注意！！！如果颜色内存足够大，不需要“合理”利用内存，就没有必要做亮度范围调整。

人对颜色的感知-图片来自知乎

gamma correction

原教程learnopgngl-Gamma校正对gamma校正的原理讲的不是太好，可能是作者自己太懂了，反而讲的略拗口。

参考知乎色彩校正中的 gamma 值是什么？循序渐进的理解比较易懂。

本章节实现效果：

未开启gamma校正的图像看起来整体偏暗些，经过gamma校正后，整体柔和一些，更逼近真实的场景。因为显示器会把低亮度的色值降下去。

未开启gamma校正	开启gamma校正

二、代码说明

1. 主程序增加4个光源

    // -------------
    glm::vec3 lightPositions[] = {
        glm::vec3(-3.0f, 0.0f, 0.0f),
        glm::vec3(-1.0f, 0.0f, 0.0f),
        glm::vec3 (1.0f, 0.0f, 0.0f),
        glm::vec3 (3.0f, 0.0f, 0.0f)
    };
    glm::vec3 lightColors[] = {
        glm::vec3(0.25),
        glm::vec3(0.50),
        glm::vec3(0.75),
        glm::vec3(1.00)
    };

2. 顶点着色器没有特殊处理，主要看片段着色器

gamma校正算法很简单，用幂运算来模拟，color的每一个分量做1.0/2.2的幂次计算

片段着色器中的其他处理也值得学习，基本包含了一个完整的光照模型的大部分元素，后面还有少量的补充，比如阴影等细节

1）环境光照（这里没有）
2）漫反射
3）反射（BlinnPhong采用半程向量的反射优化）
4）gamma校正

vec3 BlinnPhong(vec3 normal, vec3 fragPos, vec3 lightPos, vec3 lightColor)
{
    // diffuse
    vec3 lightDir = normalize(lightPos - fragPos);
    float diff = max(dot(lightDir, normal), 0.0);
    vec3 diffuse = diff * lightColor;
    
    // specular
    vec3 viewDir = normalize(viewPos - fragPos);
    vec3 reflectDir = reflect(-lightDir, normal);
    float spec = 0.0;
    vec3 halfwayDir = normalize(lightDir + viewDir);
    spec = pow(max(dot(normal, halfwayDir), 0.0), 64.0);
    vec3 specular = spec * lightColor;
    
    // simpleattenuation
    float max_distance = 1.5;
    float distance = length(lightPos - fragPos);
    float attenuation = 1.0 / (gamma ? distance * distance : distance);
    
    diffuse *= attenuation;
    specular *= attenuation;
    
    return diffuse + specular;
}

void main()
{

    vec3 color = texture(floorTexture, fs_in.TexCoords).rgb;
    vec3 lighting = vec3(0.0);
    for (int i = 0; i < 4; ++i) {
        lighting += BlinnPhong(normalize(fs_in.Normal), fs_in.FragPos, lightPositions[i], lightColors[i]);
    }
    color *= lighting;
    if(gamma)
    {
        color = pow(color, vec3(1.0 / 2.2));
    }
    FragColor = vec4(color, 1.0);
}

三、完整代码

主程序里，增加了按键 Y 和 N的处理优化，方便截屏记录笔记

1. vs

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

out VS_OUT {
    vec3 FragPos;
    vec3 Normal;
    vec2 TexCoords;
} vs_out;

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

void main()
{
    vs_out.FragPos = aPos;
    vs_out.Normal = aNormal;
    vs_out.TexCoords = aTexCoords;
    gl_Position = projection * view * vec4(aPos, 1.0);
}

2. fs

#version 330 core
out vec4 FragColor;

in VS_OUT {
    vec3 FragPos;
    vec3 Normal;
    vec2 TexCoords;
} fs_in;

uniform sampler2D floorTexture;

uniform vec3 lightPositions[4];
uniform vec3 lightColors[4];
uniform vec3 viewPos;
uniform bool gamma;

vec3 BlinnPhong(vec3 normal, vec3 fragPos, vec3 lightPos, vec3 lightColor)
{
    // diffuse
    vec3 lightDir = normalize(lightPos - fragPos);
    float diff = max(dot(lightDir, normal), 0.0);
    vec3 diffuse = diff * lightColor;
    
    // specular
    vec3 viewDir = normalize(viewPos - fragPos);
    vec3 reflectDir = reflect(-lightDir, normal);
    float spec = 0.0;
    vec3 halfwayDir = normalize(lightDir + viewDir);
    spec = pow(max(dot(normal, halfwayDir), 0.0), 64.0);
    vec3 specular = spec * lightColor;
    
    // simpleattenuation
    float max_distance = 1.5;
    float distance = length(lightPos - fragPos);
    float attenuation = 1.0 / (gamma ? distance * distance : distance);
    
    diffuse *= attenuation;
    specular *= attenuation;
    
    return diffuse + specular;
}

void main()
{

    vec3 color = texture(floorTexture, fs_in.TexCoords).rgb;
    vec3 lighting = vec3(0.0);
    for (int i = 0; i < 4; ++i) {
        lighting += BlinnPhong(normalize(fs_in.Normal), fs_in.FragPos, lightPositions[i], lightColors[i]);
    }
    color *= lighting;
    if(gamma)
    {
        color = pow(color, vec3(1.0 / 2.2));
    }
    FragColor = vec4(color, 1.0);
}

3. 主程序

#include <glad/glad.h>
#include <GLFW/glfw3.h>
#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>

#include "Shader.h"
#include "camera.h"
#include "model.h"

#include <iostream>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
void processInput(GLFWwindow *window);
unsigned int loadTexture(const char *path);
unsigned int loadCubemap(vector<std::string> faces);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;
bool blinn = false;
bool blinnKeyPressed = false;
bool gammaEnabled = false;
bool gammaKeyPressed = false;

// camera
Camera camera(glm::vec3(0.0f, 0.5f, 30.0f));
float lastX = (float)SCR_WIDTH / 2.0;
float lastY = (float)SCR_HEIGHT / 2.0;
bool firstMouse = true;

// timing
float deltaTime = 0.0f;
float lastFrame = 0.0f;

int main()
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif
    
    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "天哥学opengl", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
    glfwSetCursorPosCallback(window, mouse_callback);
    glfwSetScrollCallback(window, scroll_callback);

    // tell GLFW to capture our mouse
//    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

//    glPolygonMode(GL_FRONT_AND_BACK ,GL_LINE );
    
    // configure global opengl state
    // -----------------------------
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    // build and compile shaders
    // -------------------------
    Shader shader("1.colors.vs", "1.colors.fs");
    
    float planeVertices[] = {
        // positions            // normals         // texcoords
         10.0f, -0.5f,  10.0f,  0.0f, 1.0f, 0.0f,  10.0f,  0.0f,
        -10.0f, -0.5f,  10.0f,  0.0f, 1.0f, 0.0f,   0.0f,  0.0f,
        -10.0f, -0.5f, -10.0f,  0.0f, 1.0f, 0.0f,   0.0f, 10.0f,

         10.0f, -0.5f,  10.0f,  0.0f, 1.0f, 0.0f,  10.0f,  0.0f,
        -10.0f, -0.5f, -10.0f,  0.0f, 1.0f, 0.0f,   0.0f, 10.0f,
         10.0f, -0.5f, -10.0f,  0.0f, 1.0f, 0.0f,  10.0f, 10.0f
    };
    
    // plane VAO
     unsigned int planeVAO, planeVBO;
     glGenVertexArrays(1, &planeVAO);
     glGenBuffers(1, &planeVBO);
     glBindVertexArray(planeVAO);
     glBindBuffer(GL_ARRAY_BUFFER, planeVBO);
     glBufferData(GL_ARRAY_BUFFER, sizeof(planeVertices), planeVertices, GL_STATIC_DRAW);
     glEnableVertexAttribArray(0);
     glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
     glEnableVertexAttribArray(1);
     glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
     glEnableVertexAttribArray(2);
     glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
     glBindVertexArray(0);
    
    unsigned int floorTexture = loadTexture("resource/wood.png");
    unsigned int floorTextureGammaCorrected = loadTexture("resource/wood.png");


    shader.use();
    shader.setInt("texture1", 0);
    
    // lighting info
    // -------------
    glm::vec3 lightPositions[] = {
        glm::vec3(-3.0f, 0.0f, 0.0f),
        glm::vec3(-1.0f, 0.0f, 0.0f),
        glm::vec3 (1.0f, 0.0f, 0.0f),
        glm::vec3 (3.0f, 0.0f, 0.0f)
    };
    glm::vec3 lightColors[] = {
        glm::vec3(0.25),
        glm::vec3(0.50),
        glm::vec3(0.75),
        glm::vec3(1.00)
    };
    
    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        
        float currentFrame = glfwGetTime();
        deltaTime = currentFrame - lastFrame;
        lastFrame = currentFrame;
        
        processInput(window);
        
        glm::mat4 projection = glm::perspective(glm::radians(45.0f), (float)SCR_WIDTH / (float)SCR_HEIGHT, 1.0f, 200.0f);
        glm::mat4 view = camera.GetViewMatrix();
        
        shader.use();
        shader.setMat4("projection", projection);
        shader.setMat4("view", view);

        //set light uniforms
        glUniform3fv(glGetUniformLocation(shader.ID, "lightPositions"), 4, &lightPositions[0][0]);
        glUniform3fv(glGetUniformLocation(shader.ID, "lightColors"), 4, &lightColors[0][0]);
        shader.setVec3("viewPos", camera.Position);
        shader.setInt("gamma", gammaEnabled);
        
        // floor
        glBindVertexArray(planeVAO);
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, floorTexture);
        glDrawArrays(GL_TRIANGLES, 0, 6);
        
        std::cout << (gammaEnabled ? "Gamma enabled" : "Gamma disabled") << std::endl;
        
        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &planeVAO);
    glDeleteBuffers(1, &planeVBO);
    glfwTerminate();
    return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------

bool startRecord = false;

void processInput(GLFWwindow *window)
{
    std::cout << "B state: " << glfwGetKey(window, GLFW_KEY_B) << std::endl;
    if (glfwGetKey(window, GLFW_KEY_B) == GLFW_PRESS && !gammaKeyPressed)
    {
        std::cout << "press b--------------" << std::endl;
        gammaEnabled = !gammaEnabled;
        gammaKeyPressed = true;
    }
    if (glfwGetKey(window, GLFW_KEY_B) == GLFW_RELEASE)
    {
        std::cout << "release b" << std::endl;

        gammaKeyPressed = false;
    }
    if (glfwGetKey(window, GLFW_KEY_Y))
    {
        std::cout << "Y" << std::endl;
        startRecord = true;
        firstMouse = true;
    }
    
    if (glfwGetKey(window, GLFW_KEY_N))
    {
        std::cout << "N" << std::endl;

        startRecord = false;
    }
    
    if (startRecord) {
        return;
    }
    
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);

    if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
        camera.ProcessKeyboard(FORWARD, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
        camera.ProcessKeyboard(BACKWARD, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
        camera.ProcessKeyboard(LEFT, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
        camera.ProcessKeyboard(RIGHT, deltaTime);
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // make sure the viewport matches the new window dimensions; note that width and
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}

// glfw: whenever the mouse moves, this callback is called
// -------------------------------------------------------
void mouse_callback(GLFWwindow* window, double xpos, double ypos)
{
//    std::cout << "xpos : " << xpos << std::endl;
//    std::cout << "ypos : " << ypos << std::endl;
    
    if (startRecord) {
        return;
    }
    
    if (firstMouse)
    {
        lastX = xpos;
        lastY = ypos;
        firstMouse = false;
    }

    float xoffset = xpos - lastX;
    float yoffset = lastY - ypos; // reversed since y-coordinates go from bottom to top

    lastX = xpos;
    lastY = ypos;
    
//    std::cout << "xoffset : " << xoffset << std::endl;
//    std::cout << "yoffset : " << yoffset << std::endl;
    
    camera.ProcessMouseMovement(xoffset, yoffset);
}

// glfw: whenever the mouse scroll wheel scrolls, this callback is called
// ----------------------------------------------------------------------
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
    camera.ProcessMouseScroll(yoffset);
}

// utility function for loading a 2D texture from file
// ---------------------------------------------------
unsigned int loadTexture(char const * path)
{
    unsigned int textureID;
    glGenTextures(1, &textureID);

    int width, height, nrComponents;
    unsigned char *data = stbi_load(path, &width, &height, &nrComponents, 0);
    if (data)
    {
        GLenum format;
        if (nrComponents == 1)
            format = GL_RED;
        else if (nrComponents == 3)
            format = GL_RGB;
        else if (nrComponents == 4)
            format = GL_RGBA;

        glBindTexture(GL_TEXTURE_2D, textureID);
        glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

        stbi_image_free(data);
    }
    else
    {
        std::cout << "Texture failed to load at path: " << path << std::endl;
        stbi_image_free(data);
    }

    return textureID;
}


unsigned int loadCubemap(vector<std::string> faces)
{
    unsigned int textureID;
    glGenTextures(1, &textureID);
    glBindTexture(GL_TEXTURE_CUBE_MAP, textureID);
    
    int width, height, nrChannels;
    for (unsigned int i = 0; i < faces.size(); i++) {
        unsigned char *data = stbi_load(faces[i].c_str(), &width, &height, &nrChannels, 0);

        if (data)
        {
            glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
            stbi_image_free(data);
        }
        else
        {
            std::cout << "Cubemap texture failed to load at path: " << faces[i] << std::endl;
            stbi_image_free(data);
        }
        glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);
    }
    
    return textureID;
}

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