OpenGL 学习笔记 01 环境配置

抱歉，本文写的很乱，建议跳过代码部分。

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以下教程仅适用于Mac下的Xcode编程环境！其他的我也不会搞。

推荐教程：opengl-tutorial 

本项目Github网址

 

 

 

OpenGL太可怕了。。。必需得把学的记下来，不然绝壁忘。

 

首先贴出代码，然后分析创建一个OpenGL程序都需要什么

 #include <cstdio>
 #include <cstdlib>

 #include <GL/glew.h>

 #include <GLFW/glfw3.h>

 #include <glm/glm.hpp>
 #include <glm/gtc/matrix_transform.hpp>
 using namespace glm;
 using namespace std;

 #include <shader.hpp>
 #include <shader.cpp>

 static const GLfloat g_vertex_buffer_data[] = {
     -1.0f,-1.0f,-1.0f, // triangle 1 : begin
     -1.0f,-1.0f, 1.0f,
     -1.0f, 1.0f, 1.0f, // triangle 1 : end
     1.0f, 1.0f,-1.0f, // triangle 2 : begin
     -1.0f,-1.0f,-1.0f,
     -1.0f, 1.0f,-1.0f, // triangle 2 : end
     1.0f,-1.0f, 1.0f,
     -1.0f,-1.0f,-1.0f,
     1.0f,-1.0f,-1.0f,
     1.0f, 1.0f,-1.0f,
     1.0f,-1.0f,-1.0f,
     -1.0f,-1.0f,-1.0f,
     -1.0f,-1.0f,-1.0f,
     -1.0f, 1.0f, 1.0f,
     -1.0f, 1.0f,-1.0f,
     1.0f,-1.0f, 1.0f,
     -1.0f,-1.0f, 1.0f,
     -1.0f,-1.0f,-1.0f,
     -1.0f, 1.0f, 1.0f,
     -1.0f,-1.0f, 1.0f,
     1.0f,-1.0f, 1.0f,
     1.0f, 1.0f, 1.0f,
     1.0f,-1.0f,-1.0f,
     1.0f, 1.0f,-1.0f,
     1.0f,-1.0f,-1.0f,
     1.0f, 1.0f, 1.0f,
     1.0f,-1.0f, 1.0f,
     1.0f, 1.0f, 1.0f,
     1.0f, 1.0f,-1.0f,
     -1.0f, 1.0f,-1.0f,
     1.0f, 1.0f, 1.0f,
     -1.0f, 1.0f,-1.0f,
     -1.0f, 1.0f, 1.0f,
     1.0f, 1.0f, 1.0f,
     -1.0f, 1.0f, 1.0f,
     1.0f,-1.0f, 1.0f
 };

 //每个顶点一个颜色
 static const GLfloat g_color_buffer_data[] = {
     0.583f,  0.771f,  0.014f,
     0.609f,  0.115f,  0.436f,
     0.327f,  0.483f,  0.844f,
     0.822f,  0.569f,  0.201f,
     0.435f,  0.602f,  0.223f,
     0.310f,  0.747f,  0.185f,
     0.597f,  0.770f,  0.761f,
     0.559f,  0.436f,  0.730f,
     0.359f,  0.583f,  0.152f,
     0.483f,  0.596f,  0.789f,
     0.559f,  0.861f,  0.639f,
     0.195f,  0.548f,  0.859f,
     0.014f,  0.184f,  0.576f,
     0.771f,  0.328f,  0.970f,
     0.406f,  0.615f,  0.116f,
     0.676f,  0.977f,  0.133f,
     0.971f,  0.572f,  0.833f,
     0.140f,  0.616f,  0.489f,
     0.997f,  0.513f,  0.064f,
     0.945f,  0.719f,  0.592f,
     0.543f,  0.021f,  0.978f,
     0.279f,  0.317f,  0.505f,
     0.167f,  0.620f,  0.077f,
     0.347f,  0.857f,  0.137f,
     0.055f,  0.953f,  0.042f,
     0.714f,  0.505f,  0.345f,
     0.783f,  0.290f,  0.734f,
     0.722f,  0.645f,  0.174f,
     0.302f,  0.455f,  0.848f,
     0.225f,  0.587f,  0.040f,
     0.517f,  0.713f,  0.338f,
     0.053f,  0.959f,  0.120f,
     0.393f,  0.621f,  0.362f,
     0.673f,  0.211f,  0.457f,
     0.820f,  0.883f,  0.371f,
     0.982f,  0.099f,  0.879f
 };

 int main() {
     if(!glfwInit()) {
         fprintf(stderr, "Failed To init OpenGL\n");
     }

     // We want OpenGL 3.3
     glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, );
     glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, );
     // To make MacOS happy; should not be needed
     glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
     glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); //We don't want the old OpenGL

     // Open a window and create its OpenGL context
     // (In the accompanying source code, this variable is global)
     GLFWwindow* window;
     window = glfwCreateWindow(, , "Tutorial 01", NULL, NULL);
     if( window == NULL ){
         fprintf( stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n" );
         glfwTerminate();
         return -;
     }
     glfwMakeContextCurrent(window); // Initialize GLEW
     glewExperimental = true; // Needed in core profile

     //z-buffer
     glEnable(GL_DEPTH_TEST);
     glDepthFunc(GL_LEFT);

     if (glewInit() != GLEW_OK) {
         fprintf(stderr, "Failed to initialize GLEW\n");
         return -;
     }

     //背景颜色
     glClearColor(0.0f, 0.0f, 0.4f, 0.0f);

     //shader
     GLuint programID = LoadShaders( "/Users/jeff/IDEProjects/xcode_projects/openGL/openGL/vertex.shader", "/Users/jeff/IDEProjects/xcode_projects/openGL/openGL/fragment.shader" );

     GLuint VertexArrayID;
     glGenVertexArrays(, &VertexArrayID);
     glBindVertexArray(VertexArrayID);

     //vertex buffer
     GLuint vertexbuffer;
     glGenBuffers(, &vertexbuffer);
     glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
     glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);

     //color buffer
     GLuint colorbuffer;
     glGenBuffers(, &colorbuffer);
     glBindBuffer(GL_ARRAY_BUFFER, colorbuffer);
     glBufferData(GL_ARRAY_BUFFER, sizeof(g_color_buffer_data), g_color_buffer_data, GL_STATIC_DRAW);

     mat4 Projection = perspective(radians(70.0f), (float)/, 0.1f, .f);

     mat4 View = lookAt(vec3(, , -), vec3(,,), vec3(,,));

     mat4 Model = mat4(1.0f);

     //模型到投影转换
     mat4 mvp = Projection * View * Model;

     GLuint MatrixID = glGetUniformLocation(programID, "mvp");

     while(glfwGetKey(window, GLFW_KEY_ESCAPE) != GLFW_PRESS && !glfwWindowShouldClose(window)) {
         //每次开始时清空画布
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

         //使用shader
         glUseProgram(programID);

         //把变换矩阵送进shader
         glUniformMatrix4fv(MatrixID, , GL_FALSE, &mvp[][]);

         //画三角形
         glEnableVertexAttribArray();
         glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
         glVertexAttribPointer(, , GL_FLOAT, GL_FALSE, , (void*));

         //三角形颜色
         glEnableVertexAttribArray();
         glBindBuffer(GL_ARRAY_BUFFER, colorbuffer);
         glVertexAttribPointer(, , GL_FLOAT, GL_FALSE, , (void*));

         //draw call
         glDrawArrays(GL_TRIANGLES, ,  * );

         glDisableVertexAttribArray();
         glDisableVertexAttribArray();

         glfwSwapBuffers(window);
         glfwPollEvents();
     }
     glfwTerminate();
     return ;
 }

Code

首先是OpenGL的文件

对于OS X的用户来说，只要安装了Xcode，OpenGL也就被安装了（因为OS X用的就是这个。。）

但是还需要其他几个库，用于处理平台相关的事情或者方便我们编程，他们分别是GLFW，GLEW，GLM

在OS X上，用brew可以很方便的安装以上几个库，安装后进入下一步。

一、配置项目文件

打开Xcode，创建项目。

在如所示的的地方配置以上3个库的头文件位置。如果不知道库安装在哪了，可以用brew info glew的方式找到安装路径

配置结果如下，Libraray Search Path 不用管，后面会说

现在可以在项目的代码中正确的调用各个库的头文件了，比如

#include <GLFW/glfw3.h>

但是这样是无法编译通过的，因为lib文件还没有被链接进来，编译器会找不到头文件里面函数的定义之类的。

所以需要链接所有必要的lib文件。

链接后应该如下

点击那个“加号”添加lib

其中，4个framework直接搜就可以找到。

另外两个lib分别在GLEW和GLFW的安装目录下，比如我的路径如下：

[brew安装路径]/glew/1.13.0/lib/libGLEW.a

另一个同理，在安装目录的lib文件夹下面找得到。

glm库不用添加lib

至此所有的OpenGL代码应该就可以正常编译了，不过我上面贴的那段不行，因为我没贴全。。。

二、OpenGL程序的基本结构

首先需要按照以下顺序include一些头文件，这是魔法。

#include <GL/glew.h>
#include <GLFW/glfw3.h>

以上是最主要的头文件了，当然我们还需要不少辅助的东西，全部的include如下

#include <GL/glew.h>

#include <GLFW/glfw3.h>

#include <glm/glm.hpp>

#include <glm/gtc/matrix_transform.hpp>

using namespace glm;

#include <cstdio>

#include <cstdlib>

using namespace std;

OpenGL 3.0以后使用了可编程渲染管线，我们需要自己编写shader并编译

这里有个现成的编译shader的函数，拿来用就好

#ifndef SHADER_HPP
#define SHADER_HPP

GLuint LoadShaders(const char * vertex_file_path,const char * fragment_file_path);

#endif

shader.hpp

 #include <stdio.h>
 #include <string>
 #include <vector>
 #include <iostream>
 #include <fstream>
 #include <algorithm>
 using namespace std;

 #include <stdlib.h>
 #include <string.h>

 #include <GL/glew.h>

 #include "shader.hpp"

 GLuint LoadShaders(const char * vertex_file_path,const char * fragment_file_path){

     // Create the shaders
     GLuint VertexShaderID = glCreateShader(GL_VERTEX_SHADER);
     GLuint FragmentShaderID = glCreateShader(GL_FRAGMENT_SHADER);

     // Read the Vertex Shader code from the file
     std::string VertexShaderCode;
     std::ifstream VertexShaderStream(vertex_file_path, std::ios::in);
     if(VertexShaderStream.is_open()){
         std::string Line = "";
         while(getline(VertexShaderStream, Line))
             VertexShaderCode += "\n" + Line;
         VertexShaderStream.close();
     }else{
         printf("Impossible to open %s. Are you in the right directory ? Don't forget to read the FAQ !\n", vertex_file_path);
         getchar();
         return ;
     }

     // Read the Fragment Shader code from the file
     std::string FragmentShaderCode;
     std::ifstream FragmentShaderStream(fragment_file_path, std::ios::in);
     if(FragmentShaderStream.is_open()){
         std::string Line = "";
         while(getline(FragmentShaderStream, Line))
             FragmentShaderCode += "\n" + Line;
         FragmentShaderStream.close();
     }

     GLint Result = GL_FALSE;
     int InfoLogLength;

     // Compile Vertex Shader
     printf("Compiling shader : %s\n", vertex_file_path);
     char const * VertexSourcePointer = VertexShaderCode.c_str();
     glShaderSource(VertexShaderID, , &VertexSourcePointer , NULL);
     glCompileShader(VertexShaderID);

     // Check Vertex Shader
     glGetShaderiv(VertexShaderID, GL_COMPILE_STATUS, &Result);
     glGetShaderiv(VertexShaderID, GL_INFO_LOG_LENGTH, &InfoLogLength);
     if ( InfoLogLength >  ){
         std::vector<char> VertexShaderErrorMessage(InfoLogLength+);
         glGetShaderInfoLog(VertexShaderID, InfoLogLength, NULL, &VertexShaderErrorMessage[]);
         printf("%s\n", &VertexShaderErrorMessage[]);
     }

     // Compile Fragment Shader
     printf("Compiling shader : %s\n", fragment_file_path);
     char const * FragmentSourcePointer = FragmentShaderCode.c_str();
     glShaderSource(FragmentShaderID, , &FragmentSourcePointer , NULL);
     glCompileShader(FragmentShaderID);

     // Check Fragment Shader
     glGetShaderiv(FragmentShaderID, GL_COMPILE_STATUS, &Result);
     glGetShaderiv(FragmentShaderID, GL_INFO_LOG_LENGTH, &InfoLogLength);
     if ( InfoLogLength >  ){
         std::vector<char> FragmentShaderErrorMessage(InfoLogLength+);
         glGetShaderInfoLog(FragmentShaderID, InfoLogLength, NULL, &FragmentShaderErrorMessage[]);
         printf("%s\n", &FragmentShaderErrorMessage[]);
     }

     // Link the program
     printf("Linking program\n");
     GLuint ProgramID = glCreateProgram();
     glAttachShader(ProgramID, VertexShaderID);
     glAttachShader(ProgramID, FragmentShaderID);
     glLinkProgram(ProgramID);

     // Check the program
     glGetProgramiv(ProgramID, GL_LINK_STATUS, &Result);
     glGetProgramiv(ProgramID, GL_INFO_LOG_LENGTH, &InfoLogLength);
     if ( InfoLogLength >  ){
         std::vector<char> ProgramErrorMessage(InfoLogLength+);
         glGetProgramInfoLog(ProgramID, InfoLogLength, NULL, &ProgramErrorMessage[]);
         printf("%s\n", &ProgramErrorMessage[]);
     }

     glDetachShader(ProgramID, VertexShaderID);
     glDetachShader(ProgramID, FragmentShaderID);

     glDeleteShader(VertexShaderID);
     glDeleteShader(FragmentShaderID);

     return ProgramID;
 }

shader.cpp

别忘了#include <shader.hpp> 并把 shader.cpp 添加到项目的Compile Sources里

g_vertex_buffer_data 和 g_color_buffer_data 储存正方形的顶点位置信息和颜色信息

main 函数里:

 if(!glfwInit()) {
         fprintf(stderr, "Failed To init OpenGL\n");
     }

     // We want OpenGL 3.3
     glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, );
     glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, );
     // To make MacOS happy; should not be needed
     glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
     glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); //We don't want the old OpenGL

     // Open a window and create its OpenGL context
     // (In the accompanying source code, this variable is global)
     GLFWwindow* window;
     window = glfwCreateWindow(WIDTH, HEIGHT, "OpenGL Window", NULL, NULL);
     if( window == NULL ){
         fprintf( stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n" );
         glfwTerminate();
         return -;
     }
     glfwMakeContextCurrent(window); // Initialize GLEW
     glewExperimental = true; // Needed in core profile

     if (glewInit() != GLEW_OK) {
         fprintf(stderr, "Failed to initialize GLEW\n");
         return -;
     }

init 操作

启用z-buffer

glEnable(GL_DEPTH_TEST);

glDepthFunc(GL_LESS);

我感觉注释说的够清楚了。。。直接看代码吧

 //背景颜色
     glClearColor(0.0f, 0.0f, 0.4f, 0.0f);

     //载入并编译shader
     GLuint programID = LoadShaders( "/Users/jeff/IDEProjects/xcode_projects/openGL/openGL/vertex.shader", "/Users/jeff/IDEProjects/xcode_projects/openGL/openGL/fragment.shader" );

     //VAO
     //加速存储效率，储存VBO
     //Veretx Array Object
     GLuint VertexArrayID;
     //创建
     glGenVertexArrays(, &VertexArrayID);
     //绑定
     glBindVertexArray(VertexArrayID);

     //以下创建两个VBO
     //Vertex Buffer Object
     //用于将数据储存到显存中

     //第一个VBO
     //储存顶点数据
     GLuint vertexbuffer;
     //创建
     glGenBuffers(, &vertexbuffer);
     //绑定
     glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
     //储存数据
     glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);

     //第二个VBO
     //储存颜色信息
     //操作原理同上
     GLuint colorbuffer;
     glGenBuffers(, &colorbuffer);
     glBindBuffer(GL_ARRAY_BUFFER, colorbuffer);
     glBufferData(GL_ARRAY_BUFFER, sizeof(g_color_buffer_data), g_color_buffer_data, GL_STATIC_DRAW);

     //创建坐标变换矩阵
     //本地   ->  世界  -> 视口    ->    齐次剪裁空间       空间变换流程
     //     Model    View    Projection                 对应需要的矩阵
     //透视变换
     mat4 Projection = perspective(radians(70.0f), (float)WIDTH / HEIGHT, 0.1f, .f);
     //视口变换
     mat4 View = lookAt(vec3(, , ), vec3(,,), vec3(,,));
     //本地变换
     mat4 Model = mat4(1.0f);

     //集成本地到齐次剪裁空间的转换
     mat4 MVP = Projection * View * Model;

     //从shader中取出mvp (不是上面的MVP，特地用大小写区分了)
     //方便等会传入数据
     GLuint MatrixID = glGetUniformLocation(programID, "mvp");

     while(glfwGetKey(window, GLFW_KEY_ESCAPE) != GLFW_PRESS && !glfwWindowShouldClose(window)) {
         //每次开始时清空画布
         //同时清空z-buffer
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

         //使用shader
         glUseProgram(programID);

         //把变换矩阵送进shader
         glUniformMatrix4fv(MatrixID, , GL_FALSE, &MVP[][]);

         //把顶点信息送入shader
         //数字0对应vertex shader中的 location = 0
         glEnableVertexAttribArray();
         glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
         glVertexAttribPointer(, , GL_FLOAT, GL_FALSE, , (void*));

         //把三角形颜色送入shader
         //数字0对应vertex shader中的 location = 1
         glEnableVertexAttribArray();
         glBindBuffer(GL_ARRAY_BUFFER, colorbuffer);
         glVertexAttribPointer(, , GL_FLOAT, GL_FALSE, , (void*));

         //draw call
         glDrawArrays(GL_TRIANGLES, ,  * );

         //一定要在draw call之后关闭
         glDisableVertexAttribArray();
         glDisableVertexAttribArray();

         //切换前后缓存，将渲染好的显示出来
         glfwSwapBuffers(window);
         glfwPollEvents();
     }

main

vertex shader:

 #version  core
 layout(location = ) in vec3 vertexPosition_modelspace;
 layout(location = ) in vec3 vertexColor;

 uniform mat4 mvp;
 out vec3 fragmentColor;

 void main() {
     gl_Position = mvp * vec4(vertexPosition_modelspace, );
     fragmentColor = vertexColor;
 }

fragment shader:

 #version  core

 out vec3 color;
 in vec3 fragmentColor;

 void main() {
     color = fragmentColor;
 }

至于这两个shader干嘛的。。。我先学习学习