OpenGL大杂烩

GLFW

OpenGL只管绘图，不管窗体。所以需要手动调用系统API创建窗体，或者使用GLFW等封装好的库。

glad

OpenGL不管标准，不管实现。不同的显卡厂商有不同的OpenGL实现，因此程序编译时不知道GL函数的准确地址，只能在程序运行时动态获取。为了减少重复枯燥的函数获取步骤，可以使用glad提供的在线服务，生成所需版本的glad.h，里面包含可以直接调用的OpenGL函数。注意除了glad.h，还需要用到glad.c和其他几个头文件。glad.c放入工程，其他头文件放入系统include目录。

OpenGL的CMake参考配置

cmake_minimum_required(VERSION 3.8)
project(hellogl)

set(CMAKE_CXX_STANDARD 11)

set(SOURCE_FILES glad.c main.cpp)
add_executable(hellogl ${SOURCE_FILES})

target_link_libraries(hellogl glfw3)

用GLFW创建空窗体

#include <GLFW/glfw3.h>

int main() {
    glfwInit();
    GLFWwindow *window = glfwCreateWindow(800, 600, "Hello OpenGL", NULL, NULL);
    glfwMakeContextCurrent(window);

    while (!glfwWindowShouldClose(window)) {
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    return 0;
}

用OpenGL绘制一个三角形(可改用纯C)

#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <iostream>

void framebuffer_size_callback(GLFWwindow *window, int width, int height);

void processInput(GLFWwindow *window);

const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

const char *vertexShaderSource = "#version 330 core\n"
        "layout (location = 0) in vec3 aPos;\n"
        "void main()\n"
        "{\n"
        "    gl_Position=vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
        "}n\0";

const char *fragmentShaderSource = "#version 330 core\n"
        "out vec4 FragColor;\n"
        "void main()\n"
        "{\n"
        "    FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
        "}\n\0";

int main() {
    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

    GLFWwindow *window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL) {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }

    glfwMakeContextCurrent(window);

    if (!gladLoadGLLoader((GLADloadproc) glfwGetProcAddress)) {
        std::cout << "Failed to initialize GLAD" << std::endl;
        glfwTerminate();
        return -1;
    }

    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    int success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    }

    GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }

    GLuint shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);

    float vertices[] = {
            -0.5f, -0.5f, 0,
            0.5, -0.5f, 0,
            0, 0.5, 0
    };

    GLuint VBO, VAO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void *) 0);
    glEnableVertexAttribArray(0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);

//    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

    while (!glfwWindowShouldClose(window)) {
        processInput(window);


        glClearColor(0.2, 0.3, 0.3, 1.0);
        glClear(GL_COLOR_BUFFER_BIT);

        glUseProgram(shaderProgram);
        glBindVertexArray(VAO);
        glDrawArrays(GL_TRIANGLES, 0, 3);

        glfwSwapBuffers(window);
        glfwPollEvents();
    }

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

void framebuffer_size_callback(GLFWwindow *window, int width, int height) {
    glViewport(0, 0, width, height);
}

void processInput(GLFWwindow *window) {
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS) {
        glfwSetWindowShouldClose(window, true);
    }
}

画矩形（俩三角形）

#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <iostream>

void framebuffer_size_callback(GLFWwindow *window, int width, int height);

void processInput(GLFWwindow *window);

const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

const char *vertexShaderSource = "#version 330 core\n"
        "layout (location = 0) in vec3 aPos;\n"
        "void main()\n"
        "{\n"
        "    gl_Position=vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
        "}n\0";

const char *fragmentShaderSource = "#version 330 core\n"
        "out vec4 FragColor;\n"
        "void main()\n"
        "{\n"
        "    FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
        "}\n\0";

int main() {
    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

    GLFWwindow *window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL) {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }

    glfwMakeContextCurrent(window);

    if (!gladLoadGLLoader((GLADloadproc) glfwGetProcAddress)) {
        std::cout << "Failed to initialize GLAD" << std::endl;
        glfwTerminate();
        return -1;
    }

    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    int success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    }

    GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }

    GLuint shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);

    float vertices[] = {
            0.5f, 0.5f, 0,
            0.5f, -0.5f, 0,
            -0.5f, -0.5f, 0,
            -0.5f, 0.5f, 0
    };

    unsigned int indices[] = {
            0, 1, 3,
            1, 2, 3
    };

    GLuint VBO, VAO, EBO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glGenBuffers(1, &EBO);
    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void *) 0);
    glEnableVertexAttribArray(0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);

//    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

    while (!glfwWindowShouldClose(window)) {
        processInput(window);


        glClearColor(0.2, 0.3, 0.3, 1.0);
        glClear(GL_COLOR_BUFFER_BIT);

        glUseProgram(shaderProgram);
        glBindVertexArray(VAO);
//        glDrawArrays(GL_TRIANGLES, 0, 3);
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, (void *) 0);

        glfwSwapBuffers(window);
        glfwPollEvents();
    }

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

void framebuffer_size_callback(GLFWwindow *window, int width, int height) {
    glViewport(0, 0, width, height);
}

void processInput(GLFWwindow *window) {
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS) {
        glfwSetWindowShouldClose(window, true);
    }
}

绘制两个不同颜色的三角形

#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <iostream>

void framebuffer_size_callback(GLFWwindow *window, int width, int height);

void processInput(GLFWwindow *window);

const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

const char *vertexShaderSource = "#version 330 core\n"
        "layout (location = 0) in vec3 aPos;\n"
        "void main()\n"
        "{\n"
        "    gl_Position=vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
        "}n\0";

const char *fragmentShaderSource = "#version 330 core\n"
        "out vec4 FragColor;\n"
        "void main()\n"
        "{\n"
        "    FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
        "}\n\0";

const char *fragmentShaderSource2 = "#version 330 core\n"
        "out vec4 FragColor;\n"
        "void main()\n"
        "{\n"
        "    FragColor = vec4(0.9f, 1.0f, 0.1f, 1.0f);\n"
        "}\n\0";

int main() {
    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

    GLFWwindow *window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL) {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }

    glfwMakeContextCurrent(window);

    if (!gladLoadGLLoader((GLADloadproc) glfwGetProcAddress)) {
        std::cout << "Failed to initialize GLAD" << std::endl;
        glfwTerminate();
        return -1;
    }

    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    int success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    }

    GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }

    GLuint fragmentShader2 = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader2, 1, &fragmentShaderSource2, NULL);
    glCompileShader(fragmentShader2);
    glGetShaderiv(fragmentShader2, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(fragmentShader2, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }

    GLuint shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);

    GLuint shaderProgram2 = glCreateProgram();
    glAttachShader(shaderProgram2, vertexShader);
    glAttachShader(shaderProgram2, fragmentShader2);
    glLinkProgram(shaderProgram2);

    float vertices[] = {
            0.5f, 0.5f, 0,
            0.5f, -0.5f, 0,
            0, 0, 0,
            -0.5f, -0.5f, 0,
            -0.5f, 0.5f, 0,
            0, 0, 0
    };

    unsigned int indices[] = {
            0, 1, 3,
            1, 2, 3
    };

    GLuint VBO, VAO, EBO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glGenBuffers(1, &EBO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, 9 * sizeof(float), vertices, GL_STATIC_DRAW);

//    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
//    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    glBindVertexArray(VAO);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void *) 0);
    glEnableVertexAttribArray(0);

    GLuint VBO2, VAO2;
    glGenBuffers(1, &VBO2);
    glGenVertexArrays(1, &VAO2);
    glBindBuffer(GL_ARRAY_BUFFER, VBO2);
    glBufferData(GL_ARRAY_BUFFER, 9 * sizeof(float), vertices + 9, GL_STATIC_DRAW);
    glBindVertexArray(VAO2);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), NULL);
    glEnableVertexAttribArray(0);
//    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

    while (!glfwWindowShouldClose(window)) {
        processInput(window);


        glClearColor(0.2, 0.3, 0.3, 1.0);
        glClear(GL_COLOR_BUFFER_BIT);

        glUseProgram(shaderProgram);
        glBindVertexArray(VAO);
        glDrawArrays(GL_TRIANGLES, 0, 3);
//        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, (void *) 0);
        glBindVertexArray(0);

        glUseProgram(shaderProgram2);
        glBindVertexArray(VAO2);
        glDrawArrays(GL_TRIANGLES, 0, 3);
        glBindVertexArray(0);


        glfwSwapBuffers(window);
        glfwPollEvents();
    }

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

void framebuffer_size_callback(GLFWwindow *window, int width, int height) {
    glViewport(0, 0, width, height);
}

void processInput(GLFWwindow *window) {
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS) {
        glfwSetWindowShouldClose(window, true);
    }
}