GL example

#include <SDL2/SDL.h>
#include <GL/glew.h>

int main(int argc, char* argv[]) {
    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO) != 0) {
        return 1;
    }

    //  Sets up the GL stuff to use an 8/8/8/8 RGBA framebuffer, with a 24/8 Depth/Stencil buffer.
    SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
    SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);

    //  Specifies OpenGL 2.1, lets SDL decide the profile.  Profile's only used in 3.0 or above.
    //  If you use 3.0 or above, and you're not familiar with GL, stick with compatibility profile.
    //  GL3.0 and above are insanely difficult to use from the get-go.
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 1);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, 0);

    //  Create your window.  Note the SDL_WINDOW_OPENGL.  This is needed.
    SDL_Window* window = SDL_CreateWindow("Program Name Here", SDL_WINDOWPOS_CENTERED,
                                          SDL_WINDOWPOS_CENTERED, 640, 480, SDL_WINDOW_OPENGL);
    if (!window) {
        SDL_Quit();
        return 1;
    }

    //  Create the GL context.
    SDL_GLContext context = SDL_GL_CreateContext(window);
    if (!context) {
        SDL_DestroyWindow(window);
        SDL_Quit();
        return 1;
    }

    //  Optional.  If you link in GLEW(A separate library, look on google), this will
    //  enable all the OpenGL extensions available for you, and wrangle all the function pointers.
    //  You are advised to use GLEW.  Wrangling the pointers yourself is a nightmare to do.
    if (glewInit() != GLEW_OK) {
        SDL_GL_DeleteContext(context);
        SDL_DestroyWindow(window);
        SDL_Quit();
        return 1;
    }

    //  Make the context current for the window.
    SDL_GL_MakeCurrent(window, context);

    //  Set up matrices.  This sets up an orthographic matrix so that everything is 2D.
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0, 640, 0, 480, -1, 1);

    //  Basic variables for looping.
    SDL_Event event;
    bool isDone = false;

    //  Loop.  Check for keypresses, if escape is down, quit.
    while (!isDone) {
        while (SDL_PollEvent(&event) > 0) {
            switch(event.type) {
                case SDL_KEYDOWN:
                if (event.key.keysym.sym == SDLK_ESCAPE) {
                    isDone = true;
                }
                break;
            }
        }

        //  Clear the colorbuffer used by the GL window.
        glClear(GL_COLOR_BUFFER_BIT);

        //  Reset the modelview matrix.  glLoadIdentity() loads the identity 4x4 matrix into the modelview matrix.
        //  glMatrixMode specifies the matrix to modify.  You have GL_MODELVIEW, GL_PROJECTION, GL_TEXTURE and GL_COLOR.
        //  You'll usually use only the first two.
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();

        glColor3f(1.0, 1.0, 1.0);
        glBegin(GL_TRIANGLES);
            glVertex2f(25, 25);
            glVertex2f(50, 50);
            glVertex2f(75, 25);
        glEnd();

        //  Swaps the back and front buffers for the GL window.
        SDL_GL_SwapWindow(window);
    }

    //  Shutdown stuffs.
    SDL_GL_DeleteContext(context);
    SDL_DestroyWindow(window);
    SDL_Quit();

    return 0;
}