专栏首页音视频技术学习笔记24.opengl高级光照-Blinn-Phong

24.opengl高级光照-Blinn-Phong

这一讲原理比较简单,代码也很容易实现,Blinn在Phong的基础上提了一个小点的优化,实现起来一共两三行代码,就名垂千古。牛逼的东西往往并不复杂,越是讲的云里雾里的听不懂,往往都很虚,没有实质。

一、原理

冯氏光照在逼近真实光照和性能之间做了很好的平衡,解决了绝大部分场景的需求,也存在一些细节问题。这一章节讲Blinn-Phong通过对冯氏光照做的一些优化。

冯氏光照的问题分析:

冯氏光照

图中地板光照边缘出现明显的断裂,过渡不自然。

光照模型

在上面左图中看到的物体颜色是OK的,但是在右边这种场景下渲染出来的效果和实际看到的效果少有区别,按照冯氏光照模型,视线方向和反射方向 > 90°,导致计算的反射光强度为0,反射角计算如下,< 0就取0

float spec = pow(max(dot(viewDir, reflectDir), 0.0), 32);
vec3 specular = specularStrength * spec * lightColor;

这里原教程没有说的太细致,按照自己的理解再深入点,参考材质一章,实际每个物体对镜面高光有不同的反应,有些物体会有明显的散射,形成一个有着更大半径的高光点,如下图所示,金材质的反光比橡胶(yellow rubber)更集中,高光(散射)半径小。

材质对散射的影响

2. Blinn-Phong算法原理

1977年,James F. Blinn在冯氏着色模型上加以拓展,引入了Blinn-Phong着色模型。环境光和漫反射光计算方式不变,反射光完全改了,优化了视线和反射夹角 > 90°的情况,原理如下:

Blinn-Phong反射光模型

算法完全不同,先求光照和视线夹角的中间向量(半程向量),用半程向量和法线向量点乘来求反射因子,glsl实现代码: 1)计算出半程向量,入射光 + 视线光向量(基本的向量加法求对角线),再归一化; 2)求反射因子,和冯氏的差不多,点乘后进行幂运算

vec3 lightDir   = normalize(lightPos - FragPos);
vec3 viewDir    = normalize(viewPos - FragPos);
vec3 halfwayDir = normalize(lightDir + viewDir);

float spec = pow(max(dot(normal, halfwayDir), 0.0), shininess);
vec3 specular = lightColor * spec;

二、 实现效果

冯氏光照 vs Blinn-Phong

我自己本地参考实现的效果,PHONG 和 BLINN-PHONG并没有这么大区别,不知道原因。

blinn-phong

三、完整代码

.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);
}

.fs

#version 330 core
out vec4 FragColor;

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

uniform sampler2D floorTexture;
uniform vec3 lightPos;
uniform vec3 viewPos;
uniform bool blinn;

void main()
{
    vec3 color = texture(floorTexture, fs_in.TexCoords).rgb;
    
    // ambient
    vec3 ambient = 0.05 * color;
    
    // diffuse
    vec3 lightDir = normalize(lightPos - fs_in.FragPos);
    vec3 normal = normalize(fs_in.Normal);
    float diff = max(dot(lightDir, normal), 0.0);
    vec3 diffuse = diff * color;
    
    // specular
    vec3 viewDir = normalize(viewPos - fs_in.FragPos);
    vec3 reflectDir = reflect(-lightDir, normal);
    float spec = 0.0;
    
    if (blinn)
    {
        vec3 halfwayDir = normalize(lightDir + viewDir);
        spec = pow(max(dot(normal, halfwayDir), 0.0), 32.0);
    }
    else
    {
        vec3 reflectDir = reflect(-lightDir, normal);
        spec = pow(max(dot(viewDir, reflectDir), 0.0), 8.0);
    }
    
    vec3 specular = vec3(0.3) * spec;
    FragColor = vec4(ambient + diffuse + specular, 1.0);
}

主工程

#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;

// 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");

    shader.use();
    shader.setInt("texture1", 0);
    
    glm::vec3 lightPos(0.0f, 0.0f, 0.0f);
    // 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);
        shader.setInt("blinn", blinn);
        
        // floor
        glBindVertexArray(planeVAO);
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, floorTexture);
        glDrawArrays(GL_TRIANGLES, 0, 6);
        
        std::cout << (blinn ? "Blinn-Phong" : "Phong") << 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)
{
    if (glfwGetKey(window, GLFW_KEY_B) == GLFW_PRESS && !blinnKeyPressed) {
        blinnKeyPressed = true;
        blinn = !blinn;
    }
    if (glfwGetKey(window, GLFW_KEY_B) == GLFW_RELEASE)
    {
        blinnKeyPressed = false;
    }
    if (glfwGetKey(window, GLFW_KEY_Y))
    {
        std::cout << "Y" << std::endl;
        startRecord = 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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