Using SDL_ttf with OpenGL

Question

I'm using OpenGL and SDL to create a window in my program.

How do I use SDL_ttf with an OpenGL window?

For example I want to load a font and render some text. I want to draw the text using an SDL OpenGL surface.

Answer 1

Here's how to do it:

1. Initialize SDL and SDL_ttf, and create a window using SDL_SetVideoMode(). Make sure you pass the SDL_OPENGL flag.
2. Initialize your OpenGL scene (glViewport(), glMatrixMode() etc.).

3. Render your text with SDL_ttf using e.g. TTF_RenderUTF8_Blended(). The render functions return an SDL_surface, which you have to convert into an OpenGL texture by passing a pointer to the data (surface->pixels) to OpenGL as well as the format of the data. Like this:

   colors = surface->format->BytesPerPixel;
   if (colors == 4) {   // alpha
       if (surface->format->Rmask == 0x000000ff)
           texture_format = GL_RGBA;
       else
           texture_format = GL_BGRA;
   } else {             // no alpha
       if (surface->format->Rmask == 0x000000ff)
           texture_format = GL_RGB;
       else
           texture_format = GL_BGR;
   }
   
   glGenTextures(1, &texture);
   glBindTexture(GL_TEXTURE_2D, texture); 
   glTexImage2D(GL_TEXTURE_2D, 0, colors, surface->w, surface->h, 0,
                       texture_format, GL_UNSIGNED_BYTE, surface->pixels);
   

4. Then you can use the texture in OpenGL using glBindTexture() etc. Make sure to call SDL_GL_SwapBuffers() when you're done with drawing.