void draw_triangles ()
{
  glBegin(GL_TRIANGLES);
    glColor3f(1, 0, 0);
    glVertex3f(-1, -1, -1);

    glColor3f(0, 1, 0);
    glVertex3f(1, -1, -1);

    glColor3f(0, 0, 1);
    glVertex3f(0, 1, -1);
  glEnd();
  glFlush ();
}

gboolean render ( GtkGLArea *area, GdkGLContext *context, gpointer user_data )
{
    glViewport(0, 0, WIDTH, HEIGHT);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45, (double)WIDTH / HEIGHT, 0.1, 1000);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();    

    glClearColor ( 0.44, 0.44, 0.44, 1.0 );
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    draw_triangles ();

    return TRUE;
}

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

#include "GL/gl.h"
#include "GL/glu.h"
#include "SDL2/SDL.h"

#define WIDTH   1024
#define HEIGHT  768

bool quit = false;
SDL_Window* sdlWindow = NULL;
SDL_Event   sdlEvent;
SDL_GLContext sdlGlContext;

void draw_triangles ()
{
  glBegin(GL_TRIANGLES);
    glColor3f(1, 0, 0);
    glVertex3f(-1, -1, -3);

    glColor3f(0, 1, 0);
    glVertex3f(1, -1, -3);

    glColor3f(0, 0, 1);
    glVertex3f(0, 1, -3);
  glEnd();
  glFlush ();
}

void render ()
{
    glViewport(0, 0, WIDTH, HEIGHT);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45, (double)WIDTH / HEIGHT, 0.1, 1000);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glClearColor ( 0.44, 0.44, 0.44, 1.0 );
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    draw_triangles ();

    SDL_GL_SwapWindow(sdlWindow);
}

#undef main
int main(int args, char* argv[])
{
    if (SDL_Init(SDL_INIT_VIDEO) < 0)
    {
        printf("Couldn't init SDL2! Error: %s\n", SDL_GetError());
        return 1;
    }

    sdlWindow = SDL_CreateWindow("Example",
                    SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
                    WIDTH, HEIGHT,
                    SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE);

    if (sdlWindow == NULL)
    {
        printf("Couldn't init SDL2-window! Error: %s\n", SDL_GetError());
        return 2;
    }

    sdlGlContext = SDL_GL_CreateContext(sdlWindow);

    while (!quit)
    {
        render ();

        while(SDL_PollEvent(&sdlEvent) == 1)
        {
            if (sdlEvent.type == SDL_KEYDOWN)
            {
                switch (sdlEvent.key.keysym.sym)
                {
                    case SDLK_ESCAPE :
                        quit = true;
                        break;

                    default:
                        break;
                }
            }

            if (sdlEvent.type == SDL_QUIT)
            {
                quit = true;
            }
        }

        SDL_Delay(1);
    }

    SDL_Quit();

    return 0;
}