openGL学习笔记七： glad库及使用

  glad库与glew作用相同，可以看作它的升级版，GLAD的配置与大多数的开源库有些许的不同，GLAD使用了一个在线服务。在这里我们能够告诉GLAD需要定义的OpenGL版本，并且根据这个版本加载所有相关的OpenGL函数。

官方网址为：https://glad.dav1d.de/

安装及使用

环境：win7 VS2013

1. 下载glad：

  打开GLAD的在线服务，将语言(Language)设置为C/C++，在API选项中，选择3.3以上的OpenGL(gl)版本（我们的教程中将使用3.3版本，但更新的版本也能正常工作）。之后将模式(Profile)设置为Core，并且保证生成加载器(Generate a loader)的选项是选中的。现在可以先（暂时）忽略拓展(Extensions)中的内容。都选择完之后，点击生成(Generate)按钮来生成库文件。

下载glad.zip文件解压，就可以得到我们需要的include\glad\glad.h、include\KHR\khrplatform.h和src\glad.c这3个文件

2. opengl项目配置：

a. 项目属性 ----> C/C++ —> 附加包含目录 —> your_path\glad\include
b. 项目中添加glad.c 文件

将两个头文件目录（glad和KHR）复制到你的Includes文件夹中（注意这个Includes是配置GLFW时配置的Libraries文件夹下的子目录，而非工程下的目录），并添加glad.c文件到你的工程中。

glad库非常小，只有三个文件，可以不用编译成库直接拿来使用，在opengl项目中引入glad.c 文件，设置好头文件路径即可

3. 使用代码：

注意：glad.h 必须放在glfw3.h 或者glut.h文件之前。

#include    //这个必须放在GLFW之前
#include 

#include 

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

// settings
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"
"}\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() {
	// glfw: initialize and configure
	// ------------------------------
	glfwInit(); //glfw 初始化
	//设置OpenGL版本等信息
	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); // uncomment this statement to fix compilation on OS X
#endif

	// glfw window creation
	// --------------------
	//创建GLFW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;
	}
	//设置当前上下文
	glfwMakeContextCurrent(window);
	glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

	// glad: load all OpenGL function pointers
	// ---------------------------------------
	//把OpenGL的函数指针导入给GLAD
	if(!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) {
		std::cout << "Failed to initialize GLAD" << std::endl;
		return -1;
	}

	// build and compile our shader program
	// ------------------------------------
	// vertex shader
	int vertexShader = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
	glCompileShader(vertexShader);
	// check for shader compile errors
	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;
	}
	// fragment shader
	int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
	glCompileShader(fragmentShader);
	// check for shader compile errors
	glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
	if(!success) {
		glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
		std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
	}
	// link shaders
	int shaderProgram = glCreateProgram();
	glAttachShader(shaderProgram, vertexShader);
	glAttachShader(shaderProgram, fragmentShader);
	glLinkProgram(shaderProgram);
	// check for linking errors
	glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
	if(!success) {
		glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
		std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
	}
	glDeleteShader(vertexShader);
	glDeleteShader(fragmentShader);

	// set up vertex data (and buffer(s)) and configure vertex attributes
	// ------------------------------------------------------------------
	float vertices[] ={
		0.5f, 0.5f, 0.0f,  // top right
		0.5f, -0.5f, 0.0f,  // bottom right
		-0.5f, -0.5f, 0.0f,  // bottom left
		-0.5f, 0.5f, 0.0f   // top left 
	};
	unsigned int indices[] ={  // note that we start from 0!
		0, 1, 3,  // first Triangle
		1, 2, 3   // second Triangle
	};
	unsigned int VBO, VAO, EBO;
	glGenVertexArrays(1, &VAO);
	glGenBuffers(1, &VBO);
	glGenBuffers(1, &EBO);
	// bind the Vertex Array Object first, then bind and set vertex buffer(s), and then configure vertex attributes(s).
	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);

	// note that this is allowed, the call to glVertexAttribPointer registered VBO as the vertex attribute's bound vertex buffer object so afterwards we can safely unbind
	glBindBuffer(GL_ARRAY_BUFFER, 0);

	// remember: do NOT unbind the EBO while a VAO is active as the bound element buffer object IS stored in the VAO; keep the EBO bound.
	//glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);

	// You can unbind the VAO afterwards so other VAO calls won't accidentally modify this VAO, but this rarely happens. Modifying other
	// VAOs requires a call to glBindVertexArray anyways so we generally don't unbind VAOs (nor VBOs) when it's not directly necessary.
	glBindVertexArray(0);

	// uncomment this call to draw in wireframe polygons.
	//glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

	// render loop
	// -----------
	//循环渲染
	while(!glfwWindowShouldClose(window)) {
		// input
		// -----
		processInput(window);

		// render
		// ------
		glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT);

		// draw our first triangle
		glUseProgram(shaderProgram);
		glBindVertexArray(VAO); // seeing as we only have a single VAO there's no need to bind it every time, but we'll do so to keep things a bit more organized
		//glDrawArrays(GL_TRIANGLES, 0, 6);
		glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
		// glBindVertexArray(0); // no need to unbind it every time 

		// glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
		// -------------------------------------------------------------------------------
		//交换缓存
		glfwSwapBuffers(window);
		//事件处理
		glfwPollEvents();
	}

	// optional: de-allocate all resources once they've outlived their purpose:
	// ------------------------------------------------------------------------
	glDeleteVertexArrays(1, &VAO);
	glDeleteBuffers(1, &VBO);
	glDeleteBuffers(1, &EBO);

	// glfw: terminate, clearing all previously allocated GLFW resources.
	// ------------------------------------------------------------------
	//停止
	glfwTerminate();
	return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
//输入处理函数
void processInput(GLFWwindow *window) {
	if(glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
		glfwSetWindowShouldClose(window, true);
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
//窗口大小设置回调函数
// ---------------------------------------------------------------------------------------------
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);
}

4. 运行结果：