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c4c0d3m0n

Switching between SDL and OpenGL for drawing

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c4c0d3m0n    100
Hello all I'm trying to find out how to switch between SDL and OpenGL for drawing. In my game, I would like to use simple SDL blitting for the main menu, and then nice accelerated OpenGL for the gameplay. I threw together some code to try if it would work, but what I tried here clearly didn't work. What happens is that the following code compiles fine (g++ foo.cpp -lSDL -lGL -lGLU) but when I try to switch from SDL to OpenGL the program just crashes and SDL_GetError() isn't telling me anything...
#include <SDL/SDL.h>
#include <SDL/SDL_opengl.h>
#include <iostream>

const int QUIT_PLZ = 0 << 1;

int sdl()
{
    // Initialization
    SDL_Surface* screen = NULL;
    screen = SDL_SetVideoMode(800, 600, 32, SDL_SWSURFACE);
    if (!screen) {
        std::cout << SDL_GetError();
        return QUIT_PLZ;
    }

    SDL_WM_SetCaption("SDL", NULL);

    SDL_FillRect(screen, NULL, SDL_MapRGB(screen->format, 0x10, 0xDD, 0x12));
    SDL_Flip(screen);

    // Vars
    SDL_Event event;
    bool done = false;

    // Main loop
    while (!done)
    {
        // Event polling
        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT) return QUIT_PLZ;

            if (event.type == SDL_KEYDOWN && event.key.keysym.sym == SDLK_SPACE) {
                done = true;
            }
        }

        // Sleep
        SDL_Delay(10);
    }

    return 0;
}

int opengl()
{
    // Initialization
    if (!SDL_SetVideoMode(800, 600, 32, SDL_OPENGL)) {
        std::cout << SDL_GetError();
        return QUIT_PLZ;
    }

    SDL_WM_SetCaption("SDL + OpenGL", NULL);

    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 16);

    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glShadeModel(GL_SMOOTH);
    glEnable(GL_DEPTH_TEST);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    GLfloat height = (GLfloat) SDL_GetVideoSurface()->h;
    GLfloat width = (GLfloat) SDL_GetVideoSurface()->w;
    gluPerspective(45.0f, width / height, 0.1f, 100.0f);

    // Vars
    SDL_Event event;
    bool done = false;
    GLfloat rotation = 0.0f;

    // Main loop
    while (!done)
    {
        rotation += 1.0f;

        // Event polling
        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT) return QUIT_PLZ;

            if (event.type == SDL_KEYDOWN && event.key.keysym.sym == SDLK_SPACE) {
                done = true;
            }
        }

        // OpenGL magix
        glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

        glMatrixMode(GL_MODELVIEW);

        glLoadIdentity();
        glTranslatef(-2.0f, 0.0f, -8.0f);

        glRotatef(rotation, 0.2f, 0.7f, 0.0f);

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

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

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

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

        glLoadIdentity();
        glTranslatef(2.0f, 0.0f, -8.0f);

        SDL_GL_SwapBuffers();
        glFlush();

        // Sleep
        SDL_Delay(10);
    }

    return 0;
}

int main()
{
    SDL_Init(SDL_INIT_EVERYTHING);

    if (sdl() == QUIT_PLZ) { SDL_Quit(); return 0; }
    if (opengl() == QUIT_PLZ) { SDL_Quit(); return 0; }
    if (sdl() == QUIT_PLZ) { SDL_Quit(); return 0; }

    SDL_Quit();

    return 0;
}
I was hoping someone could clear me up on how to do this, or maybe tell me off because it's a bad idea all together to start with. If so, I'd be open for alternatives. I guess in the end I could even write the menu in OpenGL, but I'm more familiar with SDL and I would like to throw together something showable now and then program the actual game behind it later.

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