Question

I’m experimenting with the new SDL2 beta and an OpenGL3 context, and I’m having a weird problem:

If I run the SDL initialization code in my main() function, it works fine, but I want to have this code in a separete init_sdl() function.

If I put the initialization code in a separate init_sdl() function, and call this function from main(), the background color is never drawn, and the program starts to madly consume all my system’s resources.

Could someone point me to a working example where SDL is initialized in a separate function? I can’t seem to find one… Maybe this is not possible? I think I vaguely remember having a similar problem with SDL 1.2, but it’s been a few years since I’ve used that, and I don’t think I ever found a solution. In fact, this may be the reason I chose to switch to using SFML instead.

I really want to use SDL2 instead of SFML because it runs on more platforms, but not being able to separate things out into small functions is a deal breaker for me. This should be easy, am I missing something obvious?

Edit:

This works:

#include <iostream>
#include <GL/glew.h>
#include <SDL.h>
#define PROGRAM_NAME "SDL2 OpenGL3 Example"

int main(int argc, char** argv)
{
    SDL_Window* sdl2_window = 0;
    SDL_GLContext opengl3_context;

    SDL_Init(SDL_INIT_VIDEO);

    // set the opengl context version
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);

    // turn on double buffering set the depth buffer to 24 bits
    // you may need to change this to 16 or 32 for your system
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);

    // create the sdl2 window
    sdl2_window = SDL_CreateWindow(PROGRAM_NAME, SDL_WINDOWPOS_CENTERED,
            SDL_WINDOWPOS_CENTERED, 512, 512,
            SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN);

    // create the opengl3 context
    opengl3_context = SDL_GL_CreateContext(sdl2_window);

    GLenum status = glewInit();
    if (status != GLEW_OK)
    {
        std::cerr << "GLEW Error: " << glewGetErrorString(status) << "\n";
        exit(1);
    }

    // sync buffer swap with monitor's vertical refresh rate
    SDL_GL_SetSwapInterval(1);

    // set background color
    glClearColor( 1.0, 0.0, 0.0, 1.0 );

    while (true)
    {
        int status = 0;

        glClear( GL_COLOR_BUFFER_BIT );

        SDL_GL_SwapWindow(sdl2_window);

        SDL_Event event;

        while (SDL_PollEvent(&event))
        {
            switch (event.type)
            {
            case SDL_KEYDOWN:
                break;
            case SDL_KEYUP:
                // if escape is pressed, quit
                if (event.key.keysym.sym == SDLK_ESCAPE)
                    status = 1; // set status to 1 to exit main loop
                break;
            case SDL_QUIT:
                status = 1;
                break;
            }
        }

        if (status == 1) // if received instruction to quit
            break;
    }

    // delete opengl3 context, destroy sdl2 window, and shut down sdl subsystems
    SDL_GL_DeleteContext(opengl3_context);
    SDL_DestroyWindow(sdl2_window);
    SDL_Quit();

    return 0;
}

This doesn’t work:

#include <iostream>
#include <GL/glew.h>
#include <SDL.h>
#define PROGRAM_NAME "SDL2 OpenGL3 Example"

void init_sdl(SDL_Window* sdl2_window, SDL_GLContext& opengl3_context)
{
    SDL_Init(SDL_INIT_VIDEO);

    // set the opengl context version
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);

    // turn on double buffering set the depth buffer to 24 bits
    // you may need to change this to 16 or 32 for your system
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);

    // create the sdl2 window
    sdl2_window = SDL_CreateWindow(PROGRAM_NAME, SDL_WINDOWPOS_CENTERED,
            SDL_WINDOWPOS_CENTERED, 512, 512,
            SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN);

    // create the opengl3 context
    opengl3_context = SDL_GL_CreateContext(sdl2_window);
}

int main(int argc, char** argv)
{
    SDL_Window* sdl2_window = 0;
    SDL_GLContext opengl3_context;

    init_sdl(sdl2_window, opengl3_context);

    GLenum status = glewInit();
    if (status != GLEW_OK)
    {
        std::cerr << "GLEW Error: " << glewGetErrorString(status) << "\n";
        exit(1);
    }

    // sync buffer swap with monitor's vertical refresh rate
    SDL_GL_SetSwapInterval(1);

    // set background color
    glClearColor( 1.0, 0.0, 0.0, 1.0 );

    while (true)
    {
        int status = 0;

        glClear( GL_COLOR_BUFFER_BIT );

        SDL_GL_SwapWindow(sdl2_window);

        SDL_Event event;

        while (SDL_PollEvent(&event))
        {
            switch (event.type)
            {
            case SDL_KEYDOWN:
                break;
            case SDL_KEYUP:
                // if escape is pressed, quit
                if (event.key.keysym.sym == SDLK_ESCAPE)
                    status = 1; // set status to 1 to exit main loop
                break;
            case SDL_QUIT:
                status = 1;
                break;
            }
        }

        if (status == 1) // if received instruction to quit
            break;
    }

    // delete opengl3 context, destroy sdl2 window, and shut down sdl subsystems
    SDL_GL_DeleteContext(opengl3_context);
    SDL_DestroyWindow(sdl2_window);
    SDL_Quit();

    return 0;
}

Answer 1

void init_sdl(SDL_Window* sdl2_window, SDL_GLContext& opengl3_context)

Your first argument should be a reference too. Otherwise when you get back to main() sdl2_window is still zero.