六、glew库及使用

  window默认支持到OpenGL1.3，后续也没有更新，opengl并不是以API更新或者新的开发包方式更新功能，它使用了扩展方式获取高版本新的功能。

如执行扩展功能函数glArrayElementEXT：代码如下

        char* ext = (char*)glGetString(GL_EXTENSIONS); //获取该电脑显卡支持的扩展函数结合
        PFNGLARRAYELEMENTEXTPROC glArrayElementEXT = (PFNGLARRAYELEMENTEXTPROC)wglGetProcAddress("glArrayElementEXT"); //获取扩展函数glArrayElementEXT 指针
        glArrayElementEXT(0); //通过函数glArrayElementEXT 指针 调用扩展函数glArrayElementEXT 

  上面这样获取扩展功能的方式很麻烦，所以就诞生了glew，是一个跨平台的C++扩展库，方便开发者使用opengl扩展功能。

安装及使用

环境：win7 VS2013

1. 下载glew：

地址：https://github.com/Perlmint/glew-cmake

2. 打开生成glew VS工程：

在build目录下选择对应版本的VS工程打开,我使用的是VS2013打开 VC12目录下glew.sln

glew_shared ：是编译动态链接库
glew_static ： 是编译静态库

根据自己情况选择一种方式，我这里选择glew_static 。
编译之后得到glew32sd.lib

3. opengl项目配置：

a. 项目属性 ----> C/C++ —> 附加包含目录 —> your_path\glew-master\include
b. 项目属性 ----> 链接器 —> 常规 —> 附加库目录 —> your_path\lib
c. 项目属性 ----> 链接器 —> 输入 —> 附加依赖项 —> glew32sd.lib

4. 代码：

注意: glew.h要放在glfw3.h glut.h 之前，并定义宏 GLEW_STATIC

#include <iostream>    
// GLEW    
#define GLEW_STATIC    

#include <GL/glew.h>    
#include <Windows.h>
// GLFW    
#include <GLFW/glfw3.h>    
#pragma comment(lib,"winmm.lib") // 告诉连接器与这个库连接，因为我们要播放多媒体声音 
#pragma comment(linker, "/subsystem:\"windows\" /entry:\"mainCRTStartup\"" )
//#define DEBUG
// Function prototypes    
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode);

// Window dimensions    
const GLuint WIDTH = 800, HEIGHT = 600;

// The MAIN function, from here we start the application and run the game loop
//#ifdef DEBUG
//int main()
//#else
//int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow)
//#endif
int main() {
	std::cout << "Starting GLFW context, OpenGL 3.3" << std::endl;
	// Init GLFW    
	glfwInit();
	// Set all the required options for GLFW    
	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);

	// Create a GLFWwindow object that we can use for GLFW's functions    
	GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "win view", nullptr, nullptr);
	if(window == nullptr) {
		std::cout << "Failed to create GLFW window" << std::endl;
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);
	// Set the required callback functions    
	glfwSetKeyCallback(window, key_callback);
	// Set this to true so GLEW knows to use a modern approach to retrieving function pointers and extensions    
	glewExperimental = GL_TRUE;
	// Initialize GLEW to setup the OpenGL Function pointers    
	if(glewInit() != GLEW_OK) {
		std::cout << "Failed to initialize GLEW" << std::endl;
		return -1;
	}

	// Define the viewport dimensions    
	glViewport(0, 0, WIDTH, HEIGHT);

	// Game loop    
	while(!glfwWindowShouldClose(window)) {
		// Check if any events have been activiated (key pressed, mouse moved etc.) and call corresponding response functions    
		glfwPollEvents();

		// Render    
		// Clear the colorbuffer    
		glClearColor(1.0f, 0.3f, 0.3f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT);

		/* Draw a triangle */
		glBegin(GL_TRIANGLES);

		glColor3f(1.0, 0.0, 0.0);    // Red
		glVertex3f(0.0, 1.0, 0.0);

		glColor3f(0.0, 1.0, 0.0);    // Green
		glVertex3f(-1.0, -1.0, 0.0);

		glColor3f(0.0, 0.0, 1.0);    // Blue
		glVertex3f(1.0, -1.0, 0.0);

		glEnd();
		/* Swap front and back buffers */
		glfwSwapBuffers(window);
		//Sleep(20);
	}

	// Terminate GLFW, clearing any resources allocated by GLFW.    
	glfwTerminate();
	return 0;
}

// Is called whenever a key is pressed/released via GLFW    
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode) {
	std::cout << key << std::endl;
	if(key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
		glfwSetWindowShouldClose(window, GL_TRUE);
}

5. 运行结果：

来源：oschina

链接：https://my.oschina.net/u/4313085/blog/3274378