【opengl之路】3.画矩形加了解索引缓冲对象

过程

基本上和上次代码没什么区别，主要是新加了一个索引缓冲对象EBO，如果不用两个EBO画两个三角形需要重复定义两个点两次，浪费内存，所以我们通过EBO来根据顶点数组索引来画三角形节省内存，EBO用法和VAO，VBO差不多

这个glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);函数可以使图形线条化

代码

#include 
#include 
#include void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window);// 设置宽高，弄成全局变量便于修改
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;//顶点着色器
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"
"}\0";//片段着色器
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()
{// glfw初始化glfwInit();  glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);  //控制版本号为3.3glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);//创建窗口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);glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);// glad初始化，因为glad控制opengl指针。所以在调用opengl函数前先初始化gladif (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)){std::cout << "Failed to initialize GLAD" << std::endl;return -1;}//创建顶点着色器对象并去编译int vertexShader = glCreateShader(GL_VERTEX_SHADER);glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);glCompileShader(vertexShader);//检测顶点着色器是否编译成功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;}//创建片段着色器对象并去编译int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);glCompileShader(fragmentShader);//检测片段着色器是否编译成功glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);if (!success){glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;}//链接顶点着色器和片段着色器int shaderProgram = glCreateProgram();glAttachShader(shaderProgram, vertexShader);glAttachShader(shaderProgram, fragmentShader);glLinkProgram(shaderProgram);glGetShaderiv(shaderProgram, GL_LINK_STATUS, &success);if (!success) {glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;}//把着色器对象链接到程序对象以后，删除着色器对象,因为用不到了glDeleteShader(vertexShader);glDeleteShader(fragmentShader);//设置顶点数据float vertices[] = {0.5f, 0.5f, 0.0f,  //右上角顶点0.5f,-0.5f, 0.0f,  //右下角顶点 -0.5f,-0.5f, 0.0f,  //左下角顶点-0.5f, 0.5f, 0.0f   //左上角顶点};unsigned int indices[] = {0, 1, 3,  // 右边三角形1, 2, 3   // 左边三角形};unsigned int VBO, VAO,EBO;glGenVertexArrays(1, &VAO); //生成顶点数组对象(VAO),任何随后的顶点属性调用都会储存在这个VAOglGenBuffers(1, &VBO); //生成顶点缓冲对象(VBO)管理这个顶点内存glGenBuffers(1, &EBO);//生成索引缓冲对象(EBO)glBindVertexArray(VAO); //绑定VAOglBindBuffer(GL_ARRAY_BUFFER, VBO); //把新创建的缓冲绑定到GL_ARRAY_BUFFER目标上glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);//把顶点数组复制到缓冲中供OpenGL使用glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);//绑定EBOglBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);//把索引数组复制到缓冲里//顶点着色器中使用layout(location = 0)定义了position顶点属性的位置值glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);//这个函数告诉OpenGL该如何解析顶点数据glEnableVertexAttribArray(0);//使用此函数，以顶点属性位置值作为参数，启用顶点属性glBindBuffer(GL_ARRAY_BUFFER, 0);glBindVertexArray(0);//glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);//渲染循环while (!glfwWindowShouldClose(window))   //glfwWindowShouldClose函数在我们每次循环的开始前检查一次GLFW是否被要求退出，如果是的话该函数返回true然后渲染循环便结束了{//控制输入函数processInput(window);glClearColor(0, 0.3f, 0, 1.0f);glClear(GL_COLOR_BUFFER_BIT);//绘制函数glUseProgram(shaderProgram);  //渲染一个物体时要使用着色器程序glBindVertexArray(VAO);       // //glDrawArrays(GL_TRIANGLES, 0, 3);  //使用当前激活的着色器，之前定义的顶点属性配置，和VBO的顶点数据（通过VAO间接绑定）来绘制图元。glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);glfwSwapBuffers(window);  //函数会交换颜色缓冲,把后缓冲内容交换到前缓冲上glfwPollEvents(); //glfwPollEvents函数检查有没有触发什么事件（比如键盘输入、鼠标移动等）、更新窗口状态}//销毁内存分配glDeleteVertexArrays(1, &VAO);glDeleteBuffers(1, &VBO);//销毁窗口glfwTerminate();return 0;
}//输入控制
void processInput(GLFWwindow *window)
{if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)glfwSetWindowShouldClose(window, true);    //按下esc窗口退出
}//随着窗口改变视图也会跟着改变
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{glViewport(0, 0, width, height); //前两个参数窗口左下角坐标，后两个坐标窗口像素
}

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