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OpenGL-ES Ubuntu 环境搭建

此的方法在 ubuntu 和 deepin 上验证都可以成功搭建

软件包安装

sudo apt install libx11-dev
sudo apt install libglfw3 libglfw3-dev
sudo apt-get install libgles2-mesa
sudo apt-get install libgles2-mesa-dev

检查环境是否安装成功：
/usr/include 下是否有 EGL GL GLES2 GLES3 的目录

Note: 上面的环境中同时安装了 x11 和 glfw，实际上只需要安装一个自己需要的即可, x11 和 glfw 都是为 OES 环境对接到窗口系统中，
个人觉得 x11 的API 对 egl 的封装比较标准话一些，可以用于学习 egl 的api

第一个三角形

基于 glfw 实现

#include <stdio.h>
#include <time.h>
#include <GLES2/gl2.h>
#include <GLFW/glfw3.h>// Vertex Shader source code
// Vertex Shader source code
const GLchar* vertexSource ="#version 300 es\n""layout(location = 0) in vec4 position;\n""void main() {\n""    gl_Position = position;\n""}\n";// Fragment Shader source code
const GLchar* fragmentSource ="#version 300 es\n""precision mediump float;\n""out vec4 fragColor;\n""void main() {\n""    fragColor = vec4(1.0, 0.0, 0.0, 1.0);\n""}\n";int main() {printf("main testsuites enter n");// Initialize GLFWif (!glfwInit()) {fprintf(stderr, "Failed to initialize GLFW\n");return -1;}// Create a windowed mode window and its OpenGL contextGLFWwindow* window = glfwCreateWindow(640, 480, "opengles-glfw", NULL, NULL);if (!window) {fprintf(stderr, "Failed to create GLFW window\n");glfwTerminate();return -1;}// Make the window's context currentglfwMakeContextCurrent(window);// Load the OpenGL ES functionsglClearColor(0.0f, 0.0f, 0.0f, 1.0f);// Create and compile the vertex shaderGLint status;GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);glShaderSource(vertexShader, 1, &vertexSource, NULL);glCompileShader(vertexShader);// Check for compilation errorsif (status != GL_TRUE) {char buffer[512];glGetShaderInfoLog(vertexShader, 512, NULL, buffer);fprintf(stderr, "Vertex Shader Compile Error: %s\n", buffer);}// Create and compile the fragment shaderGLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);glShaderSource(fragmentShader, 1, &fragmentSource, NULL);glCompileShader(fragmentShader);glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &status);if (status != GL_TRUE) {char buffer[512];glGetShaderInfoLog(fragmentShader, 512, NULL, buffer);fprintf(stderr, "Fragment Shader Compile Error: %s\n", buffer);}// Link the vertex and fragment shader into a shader programGLuint shaderProgram = glCreateProgram();glAttachShader(shaderProgram, vertexShader);glAttachShader(shaderProgram, fragmentShader);glLinkProgram(shaderProgram);// Specify the layout of the vertex dataGLfloat vertices[] = {0.0f,  0.5f, 0.0f,0.5f, -0.5f, 0.0f,-0.5f, -0.5f, 0.0f,};GLuint vbo;glGenBuffers(1, &vbo);glBindBuffer(GL_ARRAY_BUFFER, vbo);glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);// Specify the layout of the vertex dataglUseProgram(shaderProgram);glBindBuffer(GL_ARRAY_BUFFER, vbo);glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), 0);glEnableVertexAttribArray(0);// Main loopwhile (!glfwWindowShouldClose(window)) {// calculate for extecute time,about 16.6ms every period{struct timespec currentts;static uint64_t timeInMiliSeconds = 0;clock_gettime(CLOCK_REALTIME, &currentts);uint64_t currentMilliseconds = currentts.tv_sec * 1000LL + currentts.tv_nsec / 1000000;int periodInMs = currentMilliseconds - timeInMiliSeconds;timeInMiliSeconds = currentMilliseconds;printf("current time in milliseconds %lld period:%d\n", currentMilliseconds,(periodInMs > 0 ? periodInMs : -1));}// Clear the screenglClear(GL_COLOR_BUFFER_BIT);// Draw the triangleglUseProgram(shaderProgram);glBindBuffer(GL_ARRAY_BUFFER, vbo);glEnableVertexAttribArray(0);glDrawArrays(GL_TRIANGLES, 0, 3);// Swap front and back buffersglfwSwapBuffers(window);// Poll for and process eventsglfwPollEvents();}// Clean upglDeleteBuffers(1, &vbo);glDeleteProgram(shaderProgram);glDeleteShader(vertexShader);glDeleteShader(fragmentShader);glfwDestroyWindow(window);glfwTerminate();return 0;
}

基本步骤如下：

1. GLFW初始化和窗口创建
   初始化GLFW并设置OpenGL ES上下文版本
   创建窗口并设置上下文，将创建的窗口用于opengl-es上下文，此时opengl-es和系统的窗口系统相关联 , 创建着色器，编译着色器，最近将其链接到一个程序对象

2. 编译顶点着色器和片段着色器，并将它们链接到一个程序中

3. 定义一个简单的三角形顶点数据，并绘制三角形

4. 设置视口，清除颜色缓冲区，加载顶点数据，并调用绘制命令

5. 主循环中不断交换缓冲区并处理事件，以保持窗口响应。

6. 删除程序和着色器，销毁窗口，并终止GLFW

对应的 CMakeLists.txt 实现

cmake_minimum_required(VERSION 3.27)
project(opengles_glfw C)set(CMAKE_C_STANDARD 11)find_package(PkgConfig REQUIRED)
pkg_search_module(GLFW REQUIRED glfw3)include_directories(${GLFW_INCLUDE_DIRS})add_executable(opengles_glfw main.c)
target_link_libraries(opengles_glfw ${GLFW_LIBRARIES} GLESv2)

在程序主循环中，还添加了计时相关的代码逻辑，在glfw 的模式下，主循环也是跟屏幕刷新率相同也是60Hz, 可以看到每次循环体的执行间隔都是 16.6ms

current time in milliseconds 1717986851291 period:14
current time in milliseconds 1717986851308 period:17
current time in milliseconds 1717986851324 period:16

基于 X11 实现

基于 X11 实现的 opengl-es 环境如下：

#include <malloc.h>
#include "glesbasicTriangle.h"typedef struct {GLuint programObject;
} UserData;static int initInternal(ESContext* esContext) {UserData *userData = esContext->userData;// Vertex Shader source codeconst char* vertexShaderSource ="#version 300 es                            \n""layout(location = 0) in vec4 a_position;   \n""void main() {\n""   gl_Position = a_position;\n""}\n";// Fragment Shader source codeconst char* fragmentShaderSource ="#version 300 es                            \n""precision mediump float;\n""layout(location = 0) out vec4 outColor;             \n""void main() {\n""   outColor = vec4(1.0, 0.0, 0.0, 1.0);\n""}\n";// 这里封装了 createshader-compilershader-createprogramobject-link programoobject 的操作GLuint programObject = esLoadProgram(vertexShaderSource, fragmentShaderSource);if (programObject == 0) {return GL_FALSE;}// Store the program objectuserData->programObject = programObject;return GL_TRUE;
}static int drawLoopInternal(ESContext* esContext) {// Vertex dataGLfloat vertices[] = {0.0f,  0.5f, 0.0f,-0.5f, -0.5f, 0.0f,0.5f, -0.5f, 0.0f};// Set the viewportglViewport(0, 0, 640, 480);UserData *userData = esContext->userData;glUseProgram(userData->programObject);// Clear the color bufferglClearColor(0.0, 0.0, 0.0, 1.0);glClear(GL_COLOR_BUFFER_BIT);glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, vertices);glEnableVertexAttribArray(0);// Draw the triangleglDrawArrays(GL_TRIANGLES, 0, 3);// Swap bufferseglSwapBuffers(esContext->eglDisplay, esContext->eglSurface);
}static int cleanupInternal(ESContext* esContext) {printf("%s enter!.\n",__FUNCTION__);UserData *userData = esContext->userData;glDeleteProgram(userData->programObject);eglDestroySurface(esContext->eglDisplay, esContext->eglSurface);eglDestroyContext(esContext->eglDisplay, esContext->eglContext);eglTerminate(esContext->eglDisplay);XDestroyWindow(esContext->x_display, esContext->win);XCloseDisplay(esContext->x_display);return GL_TRUE;
}int testbasicDrawTriangle(ESContext* esContext) {printf("%s enter!.\n", __FUNCTION__);esContext->userData = (UserData*)malloc(sizeof(UserData));initInternal(esContext);while (1) {XEvent xev;while (XPending(esContext->x_display)) {XNextEvent(esContext->x_display, &xev);if (xev.type == KeyPress) {cleanupInternal(esContext);}}drawLoopInternal(esContext);}}

其中在调用 testbasicDrawTriangle 之前, 还有窗口系统的准备工作需要完成，实现就是下面的函数：esCreateWindow 其他文件中实现， main 函数在调用 testbasicDrawTriangle 之前，就已经调用了 esCreateWindow 函数

GLboolean esCreateWindow ( ESContext *esContext, const char *title, GLint width, GLint height, GLuint flags )
{
// Open X11 displayEGLint majorVersion;EGLint minorVersion;Display* x_display = XOpenDisplay(NULL);if (x_display == NULL) {printf("Failed to open X display\n");return GL_FALSE;}esContext->x_display = x_display;esContext->width = width;esContext->height = height;// Create X11 windowWindow root = DefaultRootWindow(esContext->x_display);XSetWindowAttributes swa;swa.event_mask = ExposureMask | PointerMotionMask | KeyPressMask;Window win = XCreateWindow(esContext->x_display, root,0, 0, width, height, 0,CopyFromParent, InputOutput,CopyFromParent, CWEventMask,&swa);XMapWindow(esContext->x_display, win);XStoreName(esContext->x_display, win, title);esContext->win = win;// Initialize EGLEGLDisplay egl_display = eglGetDisplay((EGLNativeDisplayType)esContext->x_display);if (egl_display == EGL_NO_DISPLAY) {printf("Failed to get EGL display\n");return GL_FALSE;}esContext->eglDisplay = egl_display;if (!eglInitialize(esContext->eglDisplay, &majorVersion, &minorVersion)) {printf("Failed to initialize EGL\n");return GL_FALSE;}printf("%s majorVersion:%d minorVersion:%d \n", __FUNCTION__, majorVersion, minorVersion);// Choose an EGL configEGLint configAttribs[] = {EGL_SURFACE_TYPE, EGL_WINDOW_BIT,EGL_BLUE_SIZE, 8,EGL_GREEN_SIZE, 8,EGL_RED_SIZE, 8,EGL_DEPTH_SIZE, 8,EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,EGL_NONE};EGLint attribList[] ={EGL_RED_SIZE,       5,EGL_GREEN_SIZE,     6,EGL_BLUE_SIZE,      5,EGL_ALPHA_SIZE,     ( flags & ES_WINDOW_ALPHA ) ? 8 : EGL_DONT_CARE,EGL_DEPTH_SIZE,     ( flags & ES_WINDOW_DEPTH ) ? 8 : EGL_DONT_CARE,EGL_STENCIL_SIZE,   ( flags & ES_WINDOW_STENCIL ) ? 8 : EGL_DONT_CARE,EGL_SAMPLE_BUFFERS, ( flags & ES_WINDOW_MULTISAMPLE ) ? 1 : 0,// if EGL_KHR_create_context extension is supported, then we will use// EGL_OPENGL_ES3_BIT_KHR instead of EGL_OPENGL_ES2_BIT in the attribute listEGL_RENDERABLE_TYPE, GetContextRenderableType ( esContext->eglDisplay ),EGL_NONE};EGLConfig egl_config;EGLint numConfigs;eglChooseConfig(esContext->eglDisplay, attribList, &egl_config, 1, &numConfigs);if (numConfigs != 1) {printf("Failed to choose EGL config\n");return GL_FALSE;}// Create an EGL window surfaceEGLSurface egl_surface = eglCreateWindowSurface(esContext->eglDisplay, egl_config, (EGLNativeWindowType)esContext->win, NULL);if (egl_surface == EGL_NO_SURFACE) {printf("Failed to create EGL surface\n");return GL_FALSE;}esContext->eglSurface = egl_surface;// Create an EGL contextEGLint contextAttribs[] = { EGL_CONTEXT_CLIENT_VERSION, 2, EGL_NONE };EGLContext egl_context = eglCreateContext(esContext->eglDisplay, egl_config, EGL_NO_CONTEXT, contextAttribs);if (egl_context == EGL_NO_CONTEXT) {printf("Failed to create EGL context\n");return GL_FALSE;}esContext->eglContext = egl_context;// Make the context currentif (!eglMakeCurrent(esContext->eglDisplay, esContext->eglSurface , esContext->eglSurface , esContext->eglContext)) {printf("Failed to make EGL context current\n");return GL_FALSE;}return GL_TRUE;
}

在 esCreateWindow 的代码中，使用 x_display 关联到了 egl 的display 对象中，同时，使用在 eglCreateWindowSurface 中 使用了 x11 创建的 win handle 创建 EGLSurface

其余绘制三角形的步骤和 glfw 的基本一致
实现效果如下：