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

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3.3
	glfwWindowHint(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glad
	if (!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VAO
	glGenBuffers(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VAO
	glBindBuffer(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EBO
	glBufferData(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
}