linux gl gl.h

sudo apt-get update
sudo apt-get install libgl1-mesa-dev

#include <GL/gl.h>
#include <GL/glx.h>
#include <X11/Xlib.h>
#include <stdio.h>

Display *display;
Window window;
GLXContext context;

void init() {
    display = XOpenDisplay(NULL);
    int screen = DefaultScreen(display);
    window = XCreateSimpleWindow(display, RootWindow(display, screen), 10, 10, 800, 600, 1,
                                 BlackPixel(display, screen), WhitePixel(display, screen));
    XSelectInput(display, window, ExposureMask | KeyPressMask);
    context = glXCreateContext(display, DefaultVisual(display, screen), NULL, GL_TRUE);
    glXMakeCurrent(display, window, context);
}

void draw() {
    glClear(GL_COLOR_BUFFER_BIT);
    glBegin(GL_TRIANGLES);
    glColor3f(1.0, 0.0, 0.0); glVertex2f(-0.5, -0.5);
    glColor3f(0.0, 1.0, 0.0); glVertex2f( 0.5, -0.5);
    glColor3f(0.0, 0.0, 1.0); glVertex2f( 0.0,  0.5);
    glEnd();
    glXSwapBuffers(display, window);
}

int main(int argc, char **argv) {
    init();
    XMapWindow(display, window);
    while (1) {
        XEvent event;
        XNextEvent(display, &event);
        if (event.type == Expose) {
            draw();
        }
        if (event.type == KeyPress) {
            break;
        }
    }
    glXMakeCurrent(display, None, NULL);
    glXDestroyContext(display, context);
    XDestroyWindow(display, window);
    XCloseDisplay(display);
    return 0;
}

gcc -o opengl_example opengl_example.c -lGL -lX11 -lGLX

./opengl_example