从编译OpenGL库到我的第一个颜色变化的三角形-Shader

大学开始就在接触OpenGL，但是都是“见缝插针”式的学习，一直想着有机会走一遍OpenGL该有的学习过程。前段时间终于鼓起勇气，踏出这个久违的第一步。此前一直觉得CMake编译会很难，但是真的实践下来，发现其实也不是很难。

第一步：下载相关的材料，编译OpenGL库，并测试。

1.下载glfw包，git形式：http://192.168.1.108/svn/webgl/client/branch/1.0.3  网址：http://www.glfw.org/

2.下载CMake安装包，网址：https://cmake.org/

3.下载glew包，git形式： https://github.com/nigels-com/glew.git glew 网址：http://glew.sourceforge.net/

注：这个网址下的glew包的对应VS版本：VC6、VC10、VC12、VC14、VC15，如果是更高的VS版本，这需要另外找glew包，建议是到官网下。

 

（1）首先安装CMake软件。

（2）在电脑里任意目录下新建一个文件专门安放OpenGL相关库，例如文件夹名“OpenGL”，子目录有“include”和“libs”。

（3）由于glew不需要经过Cmake，可直接使用VS打开下载的glew>build目录下的对应VS版本的工程项目，进行编译。编译成功之后，打开glew目录下的lib->Debug->Win32，

将glew32d.lib和glew32sd.lib文件拷贝到上述的“libs”目录下；glew目录下的include目录下的整个“GL”文件夹拷贝到上述的“include”目录下。

（4）在glfw目录下新建一个“build”文件夹，打开CMake软件（点击运行cmake-gui.exe程序），在<where to the source code>处选择你的glfw所在的目录，在<where to build the binaries> 处选择刚刚新建的“build”文件夹所在的目录，如图：

然后点击<Configure> 选择你的VS版本，其他选项默认，之后点击“Finish”，等待几秒最后点击“Generate”按钮。之后就可以关闭CMake了。

在刚刚新建的“build”目录中，会增加一些文件，双击GLFW.sln，启动VS，按F7键等待工程生成完毕，在刚新建的build目录，build->src->Debug目录下会有一个glfw3.lib，这是我们所需要的，将glfw3.lib拷贝到上述的“OpenGL”->“libs”目录下。在glfw->include目录下会生成“GLFW”，将其整个拷贝到上述的“OpenGL”->“include”目录下。

到此，OpenGL库生成完毕。

（5）项目测试。

打开VS软件，新建一个空的C++工程项目，在项目属性中<配置属性>-><VC++目录>-><包含目录>添加上述“OpenGL”->“include”所在的目录，在<库目录>中添加上述“OpenGL”->“libs”所在的目录，在<链接器>-><输入>-><附加依赖项>中添加文件：glfw3.lib   glew32sd.lib   opengl32.lib，其中opengl32.lib是安装VS的时候直接就包含了。

新建一个.cpp文件，复制下面的代码:

 

  #include <iostream> // GLEW #define GLEW_STATIC #include <GL/glew.h> // GLFW #include <GLFW/glfw3.h> // Window dimensions const GLuint WIDTH = 800, HEIGHT = 600; // The MAIN function, from here we start the application and run the game loop 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, "LearnOpenGL", nullptr, nullptr); if (window == nullptr) { std::cout << "Failed to create GLFW window" << std::endl; glfwTerminate(); return -1; } glfwMakeContextCurrent(window); // 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 int width, height; glfwGetFramebufferSize(window, &width, &height); 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(); // Swap the screen buffers glfwSwapBuffers(window); } // Terminate GLFW, clearing any resources allocated by GLFW. glfwTerminate(); return 0; }

然后进行编译即可。 第二步：创建我的变化三角形-着色器 同样新建一个C++空工程项目，使用着色器来显示绘制的三角形。关于着色器，这里说的很详细。完整的代码可参见下面。

#include <iostream> #include <cmath> // GLEW #define GLEW_STATIC #include <GL/glew.h> // GLFW #include <GLFW/glfw3.h> // Function prototypes void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode); // Window dimensions const GLuint WIDTH = 800, HEIGHT = 600; // Shaders const GLchar* vertexShaderSource = "#version 330 core\n" "layout (location = 0) in vec3 position;\n" "layout (location = 1) in vec3 color;\n" "out vec3 ourColor;\n" "void main()\n" "{\n" "gl_Position = vec4(position, 1.0);\n" "ourColor = color;\n" "}\0"; const GLchar* fragmentShaderSource = "#version 330 core\n" "out vec4 color;\n" "uniform vec4 ourColor;\n" "void main()\n" "{\n" "color = ourColor;\n" "}\n\0"; // The MAIN function, from here we start the application and run the game loop int main() { // 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, "LearnOpenGL", nullptr, nullptr); 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 glewInit(); // Define the viewport dimensions glViewport(0, 0, WIDTH, HEIGHT); // Build and compile our shader program // Vertex shader GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER); glShaderSource(vertexShader, 1, &vertexShaderSource, NULL); glCompileShader(vertexShader); // Check for compile time errors GLint success; GLchar 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 GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER); glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL); glCompileShader(fragmentShader); // Check for compile time 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 GLuint 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 attribute pointers GLfloat vertices[] = { // Positions 0.5f, -0.5f, 0.0f, // Bottom Right -0.5f, -0.5f, 0.0f, // Bottom Left 0.0f, 0.5f, 0.0f // Top }; GLuint VBO, VAO; glGenVertexArrays(1, &VAO); glGenBuffers(1, &VBO); // Bind the Vertex Array Object first, then bind and set vertex buffer(s) and attribute pointer(s). glBindVertexArray(VAO); glBindBuffer(GL_ARRAY_BUFFER, VBO); glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW); // Position attribute glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0); glEnableVertexAttribArray(0); glBindVertexArray(0); // Unbind VAO // 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(0.2f, 0.3f, 0.3f, 1.0f); glClear(GL_COLOR_BUFFER_BIT); // Be sure to activate the shader glUseProgram(shaderProgram); // Update the uniform color GLfloat timeValue = glfwGetTime(); GLfloat greenValue = (sin(timeValue) / 2) + 0.5; GLint vertexColorLocation = glGetUniformLocation(shaderProgram, "ourColor"); glUniform4f(vertexColorLocation, 0.0f, greenValue, 0.0f, 1.0f); // Draw the triangle glBindVertexArray(VAO); glDrawArrays(GL_TRIANGLES, 0, 3); glBindVertexArray(0); // Swap the screen buffers glfwSwapBuffers(window); } // Properly de-allocate all resources once they've outlived their purpose glDeleteVertexArrays(1, &VAO); glDeleteBuffers(1, &VBO); // 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) { if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS) glfwSetWindowShouldClose(window, GL_TRUE); }

最后的显示效果如图：