opengl---基本绘制（一）
基本绘制（一）
- glad与glew作用类似，实现对底层OpenGL接口封装
- glfw与glut作用类似，创建窗口界面
- glut年代久远，现在用glfw居多，可使用glfw+glad组合方式，比如这个教程：https://learnopengl-cn.github.io/
OpenGL有很多扩展库，下面我们一一了解一下，现在开发过程中，我们推荐使用opengl+glew+glfw组合方案。
opengl32.lib：（DLL)是MS为openGL能够在window环境下工作设计的函数库，这个库的工作很简单。如果你的机器上存在硬件加速的GL驱动，调用该驱动，否则用软件的方法实现。
包含gl.h文件并使用了里面的函数必须将opengl32.lib加入你的工程。
glew：不同的显卡公司，也会发布一些只有自家显卡才支 持的扩展函数，你要想用这数涵数，不得不去寻找最新的glext.h,有了GLEW扩展库，你就再也不用为找不到函数的接口而烦恼，因为GLEW能自动识别你的平台所支持的全部OpenGL高级扩展函数。也就是说，只要包含一个glew.h头文件，你就能使用gl,glu,glext,wgl,glx的全部函数。
glfw：一个轻量级的，开源的，跨平台的library。支持OpenGL及OpenGL ES，用来管理窗口，读取输入，处理事件等。因为OpenGL没有窗口管理的功能，所以很多热心的人写了工具来支持这些功能，比如早期的glut，现在的freeglut等。那么GLFW有何优势呢？glut太老了，最后一个版本还是90年代的。freeglut完全兼容glut，算是glut的代替品，功能齐全，但是bug太多。稳定性也不好（不是我说的啊），GLFW应运而生。
Equalizer（均衡器）是一个用于可伸缩OpenGL应用程序的开源编程接口和资源管理系统。均衡器应用程序可以部署在任何可视化系统上，从单管工作站到大型图形集群。
GLee是一个免费的跨平台扩展加载库，可以减轻应用程序的负担。GLee使得检查OpenGL扩展和核心版本的可用性变得容易，无需您的努力就可以自动设置入口点。
GLUS是一个开源的C库，它提供了一个硬件和操作系统抽象，以及使用OpenGL、opengles或OpenVG进行图形编程所需的许多函数。
OpenGL Mathematics （OpenGL 数学，GLM）是基于OpenGL着色语言（GLSL）规范的三维软件的C++数学库。
libktx是KTX工具集的一部分，是一个函数库，用于编写KTX格式的文件并从中实例化GL纹理。
OpenSceneGraph是一个高级的3D图形工具包，它在提供许多自己的功能的同时，还公开了OpenGL的功能。OpenSceneGraph拥有一个庞大的用户社区，已经被用于可视化仿真、游戏、虚拟现实、科学可视化和建模。
glu则是在gl基础上的扩展，如上面所说，他实际上已经是OpenGL的一部分了。他的函数都是以glu开头的（区别于gl函数族），你使用的gluPerspective就是这样的函数。要使用这些函数，必须将glu32.lib链接到你的工程中。
glut是另外一个opengl的扩展库，现在被广泛的使用，其中函数都以glut打头，使用时要连接glut32.lib。顺便说一句，SGI也有在windows环境下的opengl驱动，里面的库文件名改了一下，去掉了32:opengl.lib和glu.lib。这个库只支持32位，已经被淘汰了，替代品是freeglut。
https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/
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); // 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(); 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 // glfw window creation // -------------------- 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: load all OpenGL function pointers // --------------------------------------- if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) { std::cout << "Failed to initialize GLAD" << std::endl; return -1; } // build and compile our shader program // ------------------------------------ // vertex shader unsigned 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 unsigned 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 unsigned 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 // ----------- 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.) // ------------------------------------------------------------------------------- glfwSwapBuffers(window); glfwPollEvents(); } // optional: de-allocate all resources once they've outlived their purpose: // ------------------------------------------------------------------------ glDeleteVertexArrays(1, &VAO); glDeleteBuffers(1, &VBO); glDeleteBuffers(1, &EBO); glDeleteProgram(shaderProgram); // glfw: terminate, clearing all previously allocated GLFW resources. // ------------------------------------------------------------------ glfwTerminate(); return 0; } // process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly // --------------------------------------------------------------------------------------------------------- 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 // --------------------------------------------------------------------------------------------- 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); }
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