[SDL] My first program that uses the SDL TTF library..and it doesn't work

[Eric Lilja]

Consider the following C++ program (sorry, not minimal, but still 
simple). It runs without assertions being triggered or error messages 
being shown but I don't see any text output at all (the rest works as 
expected):
#include <SDL.h>
#include <SDL_ttf.h>
#include <GL/gl.h>

#include <cassert>
#include <iostream>
#include <string>

using namespace std;

static int shade_models[] = { GL_FLAT, GL_SMOOTH };

float square_vertices[][2] =
{
    {-0.5f, -0.5f},
    {-0.5f, 0.5f},
    {0.5f, 0.5f},
    {0.5f, -0.5f}
};

static SDL_Surface *
obtain_text_surface(const string& fontname, const string& str)
{
    int retval = TTF_Init();

    assert(retval != -1);

    // TODO: Fix font leakage
    TTF_Font *font = TTF_OpenFont(fontname.c_str(), 12);

    assert(font);

    SDL_Color color={0, 0, 0xFF, 0};

    return TTF_RenderText_Blended(font, str.c_str(), color);
}

static void
display(SDL_Surface * screen, SDL_Surface *text_surface)
{
    glClear(GL_COLOR_BUFFER_BIT);
	
    glBegin(GL_POLYGON);

    glColor3ub(0xFF, 0x38, 0x59);
    glVertex2fv(square_vertices[0]);

    glColor3ub(0xa0, 0x0E, 0x10);
    glVertex2fv(square_vertices[1]);

    glColor3ub(0x90, 0x90, 0x90);
    glVertex2fv(square_vertices[2]);

    glColor3ub(0x01, 0x01, 0x20);
    glVertex2fv(square_vertices[3]);

    glEnd();

    SDL_Rect dest = {0,0,0,0};

    if (SDL_BlitSurface(text_surface, NULL, screen, &dest) == -1)
    {
       cout << "SDL_BlitSurface() failed. SDL_GetError() says: "
            << SDL_GetError() << endl;
    }

    SDL_GL_SwapBuffers();
}

int
main(int argc, char *argv[])
{
    (void)argc;
    (void)argv;

    int retval = SDL_Init(SDL_INIT_VIDEO);

    assert(retval == 0);

    SDL_Surface *screen = SDL_SetVideoMode(640, 480, 0, SDL_OPENGL);

    assert(screen != NULL);

    SDL_WM_SetCaption("Simple 1-3 (using SDL)", NULL);

    glShadeModel(GL_FLAT);

    SDL_Surface *text_surface =
       obtain_text_surface("arial.ttf", "hello world");

    assert(text_surface);

    SDL_Event event;
    bool run_mainloop = true;

    while (run_mainloop == true)
    {
       while (SDL_PollEvent(&event))
       {
          switch (event.type)
          {
             case SDL_QUIT:
                run_mainloop = false;

                break;
             case SDL_KEYDOWN:
                switch (event.key.keysym.sym)
                {
                   case SDLK_ESCAPE:
                   case 'q': /* Catches 'Q' too. */
                      run_mainloop = false;

                      break;
                   case 't': /* Catches 'T' too, toggles shade mode. */
                      static int i = 0;

                      glShadeModel(shade_models[++i % 2]);

                      break;
                   default:
                      ;
                }

                break;
          }
       }

       display(screen, text_surface);

       SDL_Delay(50);
    }

    SDL_FreeSurface(text_surface);

    SDL_Quit();
}

If I replace the call to TTF_RenderText_Blended() with one to _Solid() 
it returns NULL...

Any ideas?

/ E