int sgeSetRenderMode(sgeRenderMode mode)
{
    if (!(sgeDefaultContext)) {
        fprintf(stderr, "%s: SGE must be initialised first.\n", __func__);
        return -1;
    }
    sgeDefaultContext->RenderMode = mode;
    /* Set up OpenGL for 2D rendering if necessary.
     */
    if (mode == SGE_OPENGL2D) {
        if (!(sgeDefaultContext->Screen)) {
            sgeSetError("%s: Video mode must be set first.\n",
                                __func__);
            return -1;
        }
        SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
        glEnable(GL_TEXTURE_2D);
        glClearColor(0.f, 0.f, 0.f, 0.f);
        glViewport(0, 0, sgeDefaultContext->Screen->w, sgeDefaultContext->Screen->h);
        glClear(GL_COLOR_BUFFER_BIT);
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrtho(0.f, sgeDefaultContext->Screen->w, sgeDefaultContext->Screen->h, 0.f, -1.f, 1.f);
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
    }
    return 0;
}