OpenGL基础20：镜面光照

一、镜面光照

前面物体已经拥有了环境光和漫反射光，现在再加上镜面光照就完美了，镜面光照的效果是：当我们去看光被物体所反射的那个方向的时候，会看到一个高光

和镜面反射一样，不过我们希望得到的是下图 $R$ 与 $V$ 的夹角

我们在求漫反射光照时，已经获得了向量 $N$ 和 $L$

接下来我们求出 $V$ ，Viewer正是我们的摄像机：

GLint viewPosLoc = glGetUniformLocation(shaderObj.Program, "viewPos");
glUniform3f(viewPosLoc, camera.Position.x, camera.Position.y, camera.Position.z);

然后在着色器中接收这个viewPos，定义两个参数：镜面强度(Specular Intensity) 和反光度(Shininess)

镜面强度(Specular Intensity)：和物体材质相关，往往越大则越亮
反光度(Shininess)：一个物体的发光值越高，反射光的能力越强，散射得越少，高光点越小

先默认为 1 和 32

int power = 32;
float specularStrength = 1f;

之后就是计算出 $R$ 和 $V$

reflect(A, B)：获得 A 关于 B 的对称向量

vec3 viewDir = normalize(viewPos - FragPosIn);
vec3 reflectDir = reflect(-lightDir, norm);

剩下就是和漫反射一样，计算镜面光分量：

镜面反射系数定义为： $\text {spec}=\cos (\theta)^{s}$

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

搞定！效果如下：

二、Gouraud着色

Phong着色：光照在片段着色器中计算
Gouraud着色：光照在顶点着色器中计算

显然，之前的光照计算，例子都是Phong着色，因为片段数量是远远超过顶点数量的，所以Phong着色会要真实得多，但是也相对更耗性能

三、测试

可以尝试让光源动起来：看下整体效果

lightPos.x = 1.0f + sin(glfwGetTime()) * 2.0f;
lightPos.y = sin(glfwGetTime() / 2.0f) * 1.0f;

当然也可以在观察空间中计算冯氏光照，区别就是：观察空间的观察点一定位于(0, 0, 0)，且需要在顶点着色器中计算法向量和光照物体位置时多乘上观察矩阵，完整代码如下：

#version 330 core
layout (location = 0) in vec3 position;
layout (location = 1) in vec2 texture;
layout (location = 2) in vec3 normal;
out vec2 texIn;
out vec3 normalIn;
out vec3 fragPosIn;
out vec3 lightPosIn;
uniform vec3 lightPos;
uniform mat4 model;             //模型矩阵
uniform mat4 view;              //观察矩阵
uniform mat4 projection;        //投影矩阵
void main()
{
    gl_Position = projection * view * model * vec4(position, 1.0);
    //texIn = vec2(texture.x, 1.0f - texture.y);
    fragPosIn = vec3(view * model * vec4(position, 1.0f));
    normalIn = mat3(transpose(inverse(view * model))) * normal;
    lightPosIn = vec3(view * vec4(lightPos, 1.0f));
}

/////////////////////////////////////////////////////////////////////////////////

#version 330 core
out vec4 color;
uniform vec3 objectColor;
uniform vec3 lightColor;
uniform vec3 viewPos;
in vec3 lightPosIn;
in vec3 fragPosIn;
in vec2 texIn;
in vec3 normalIn;
uniform sampler2D texOutA;
void main()
{
    //环境光
    float ambientStrength = 0.1f;
    vec3 ambient = ambientStrength * lightColor;

    //漫反射光
    vec3 norm = normalize(normalIn);
    vec3 lightDir = normalize(lightPosIn - fragPosIn);
    float diff = max(dot(norm, lightDir), 0.0f);
    vec3 diffuse = diff * lightColor;

    //镜面光
    int power = 32;
    float specularStrength = 1f;
    vec3 viewDir = normalize(-fragPosIn);
    vec3 reflectDir = reflect(-lightDir, norm);
    float spec = pow(max(dot(viewDir, reflectDir), 0.0), power);
    vec3 specular = specularStrength * spec * lightColor;

    //混合
    vec3 result = (ambient + diffuse + specular) * objectColor;
    color = vec4(result, 1.0f);
}

main.cpp：

#include<iostream>
#include<opengl/glew.h>
#define GLEW_STATIC
#include<GLFW/glfw3.h>
#include"Camera.h"
#include<glm/glm.hpp>
#include<glm/gtc/matrix_transform.hpp>
#include<glm/gtc/type_ptr.hpp>
#include"Shader.h"
#include<opengl/freeglut.h>
#include<SOIL.h>

bool keys[1024];
Camera camera;
GLfloat lastX, lastY;
bool firstMouse = true;
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void cameraMove();
glm::vec3 lightPos(1.2f, 1.0f, 2.0f);
const GLuint WIDTH = 800, HEIGHT = 600;

int main()
{
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);

    GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "LearnOpenGL", nullptr, nullptr);
    glfwMakeContextCurrent(window);
    glfwSetKeyCallback(window, key_callback);
    glfwSetCursorPosCallback(window, mouse_callback);
    glfwSetScrollCallback(window, scroll_callback);

    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);
    glewExperimental = GL_TRUE;
    glewInit();

    int width, height;
    glfwGetFramebufferSize(window, &width, &height);
    glViewport(0, 0, width, height);

    Shader shaderObj("ObjVShader.txt", "ObjFShader.txt");
    Shader shaderLight("LightVShader.txt", "LightFShader.txt");

    GLfloat vertices[] = 
    {
        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
         0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
        -0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,

        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,
        -0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,
        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,

        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,
        -0.5f,  0.5f, -0.5f, -1.0f,  0.0f,  0.0f,
        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,
        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,
        -0.5f, -0.5f,  0.5f, -1.0f,  0.0f,  0.0f,
        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,

         0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,
         0.5f,  0.5f, -0.5f,  1.0f,  0.0f,  0.0f,
         0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,
         0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,
         0.5f, -0.5f,  0.5f,  1.0f,  0.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,

        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,
         0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,
         0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,
         0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,

        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,
        -0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,
        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f
    };
    GLuint VBO, VAO, texture;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glGenTextures(1, &texture);

    glBindVertexArray(VAO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBindTexture(GL_TEXTURE_2D, texture);

    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (GLvoid*)0);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(2, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
    glEnableVertexAttribArray(2);
    /*glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
    glEnableVertexAttribArray(1);

    int picWidth, picHeight;
    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);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    unsigned char* image = SOIL_load_image("Texture/wood.jpg", &picWidth, &picHeight, 0, SOIL_LOAD_RGB);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, picWidth, picHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
    glGenerateMipmap(GL_TEXTURE_2D);
    SOIL_free_image_data(image);
    glBindTexture(GL_TEXTURE_2D, 0);*/

    GLuint lightVAO;
    glGenVertexArrays(1, &lightVAO);
    glBindVertexArray(lightVAO);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (GLvoid*)0);
    //VBO数据已经绑定且我们就用之前的顶点数据，所以无需再管理VBO
    glEnableVertexAttribArray(0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);

    glEnable(GL_DEPTH_TEST);
    while (!glfwWindowShouldClose(window))
    {
        glfwPollEvents();
        glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        glClear(GL_DEPTH_BUFFER_BIT);
        cameraMove();

        //glBindTexture(GL_TEXTURE_2D, 0);
        shaderLight.Use();
        lightPos.x = 1.0f + sin(glfwGetTime()) * 2.0f;
        lightPos.y = sin(glfwGetTime() / 2.0f) * 1.0f;
        glm::mat4 view = camera.GetViewMatrix();
        glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (GLfloat)WIDTH / (GLfloat)HEIGHT, 0.1f, 100.0f);
        glm::mat4 model = glm::translate(glm::mat4(1.0f), lightPos);
        model = glm::scale(model, glm::vec3(0.2f));
        GLint modelLoc = glGetUniformLocation(shaderLight.Program, "model");
        GLint viewLoc = glGetUniformLocation(shaderLight.Program, "view");
        GLint projLoc = glGetUniformLocation(shaderLight.Program, "projection");
        glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));
        glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view));
        glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(projection));

        glBindVertexArray(lightVAO);
        glDrawArrays(GL_TRIANGLES, 0, 36);

        //glBindTexture(GL_TEXTURE_2D, texture);
        shaderObj.Use();
        GLint objectColorLoc = glGetUniformLocation(shaderObj.Program, "objectColor");
        GLint lightColorLoc = glGetUniformLocation(shaderObj.Program, "lightColor");
        GLint lightPosLoc = glGetUniformLocation(shaderObj.Program, "lightPos");
        GLint viewPosLoc = glGetUniformLocation(shaderObj.Program, "viewPos");
        glUniform3f(viewPosLoc, camera.Position.x, camera.Position.y, camera.Position.z);
        glUniform3f(lightPosLoc, lightPos.x, lightPos.y, lightPos.z);
        glUniform3f(objectColorLoc, 1.0f, 0.5f, 0.31f);     //物体反射颜色
        glUniform3f(lightColorLoc, 1.0f, 1.0f, 1.0f);       //光源：默认为白色
        model = glm::mat4(1.0f);
        model = glm::rotate(model, glm::radians(57.0f), glm::vec3(-0.5f, 1.0f, 0.0f));
        modelLoc = glGetUniformLocation(shaderObj.Program, "model");
        viewLoc = glGetUniformLocation(shaderObj.Program, "view");
        projLoc = glGetUniformLocation(shaderObj.Program, "projection");
        glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));
        glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view));
        glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(projection));

        glBindVertexArray(VAO);
        glDrawArrays(GL_TRIANGLES, 0, 36);

        glBindVertexArray(0);
        glfwSwapBuffers(window);
    }
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glfwTerminate();
    return 0;
}


GLfloat deltaTime = 0.0f;
GLfloat lastFrame = 0.0f;
void cameraMove()
{
    GLfloat currentFrame = glfwGetTime();
    deltaTime = currentFrame - lastFrame;
    lastFrame = currentFrame;

    GLfloat cameraSpeed = 1.0f * deltaTime;
    if (keys[GLFW_KEY_W])
        camera.ProcessKeyboard(Camera_Movement(FORWARD), deltaTime);
    if (keys[GLFW_KEY_S])
        camera.ProcessKeyboard(Camera_Movement(BACKWARD), deltaTime);
    if (keys[GLFW_KEY_A])
        camera.ProcessKeyboard(Camera_Movement(LEFT), deltaTime);
    if (keys[GLFW_KEY_D])
        camera.ProcessKeyboard(Camera_Movement(RIGHT), deltaTime);
}

void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode)
{
    if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
        glfwSetWindowShouldClose(window, GL_TRUE);
    if (action == GLFW_PRESS)           //如果当前是按下操作
        keys[key] = true;
    else if (action == GLFW_RELEASE)            //松开键盘
        keys[key] = false;
}

void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
    camera.ProcessMouseScroll(yoffset);
}

void mouse_callback(GLFWwindow* window, double xpos, double ypos)
{
    if (firstMouse)
    {
        lastX = xpos;
        lastY = ypos;
        firstMouse = false;
    }
    GLfloat xoffset = xpos - lastX;
    GLfloat yoffset = lastY - ypos;
    lastX = xpos;
    lastY = ypos;
    
    GLfloat sensitivity = 0.05;
    xoffset *= sensitivity;
    yoffset *= sensitivity;
    
    camera.ProcessMouseMovement(xoffset, yoffset);
}

OpenGL基础20：镜面光照

一、镜面光照

二、Gouraud着色

三、测试

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