Tute: Introduction to SDL

Download the framework code.

Note that depending on how much you remember from last semester, this tute could take several hours. Make sure you complete the tute before next week, as the following tutes will build on the code you write in this one.

1. Open a terminal and extract the code:

   tar xzf tute-sdl.tar.gz
   cd tute-sdl
   

2. Compile and run the example:

   make
   ./example
   

   The included files are:

   Makefile

   A simple Makefile for compiling the code. If you add source files or headers be sure to change the HEADERS and OBJECTS variables.

   sdl-base.c, sdl-base.h

   This implements the standard event loop in main, and also provides a frame-rate counter (see below). It provides hooks for handling events and drawing the frame.

   example.c

   An example of how to use sdl-base, that just displays a purple background.

   The main function in sdl-base.c implements the standard event loop that was shown in the lecture:

   int main(int argc, char **argv)
   {
       SDL_Init(SDL_INIT_VIDEO | ...);
       screen = SDL_SetVideoMode(...);
   
       init();
       while (!quit)
       {
           /* Process all pending events */
           while (SDL_PollEvent(&ev))
           {
               switch (ev.type)
               {
                   ...
                   default:
                       event(&ev);
               }
           }
   
           /* Refresh display and flip buffers */
           display(screen);
           SDL_GL_SwapBuffers();
   
           /* ... */
       }
   
       return EXIT_SUCCESS;
   }
   

   Note how most events are passed to event, which is an undefinded function, and that every frame display is called to render the frame to the SDL_Surface.

   example.c implements these four functions:

   void init()
   {
   }
   
   void reshape(int width, int height)
   {
   }
   
   void display(SDL_Surface *screen)
   {
       glClearColor(1, 0, 1, 0);
       glClear(GL_COLOR_BUFFER_BIT);
       printf("% 5d FPS\r", fps);
       fflush(stdout);
   }
   
   void update(int milliseconds)
   {
   }
   
   void event(SDL_Event *event)
   {
   }
   

3. Make a copy of example.c, called tute-sdl.c, and make the required changes to the Makefile so that it compiles instead of (or as well as) example.c.

4. Modify tute-sdl.c so that it sets up a projection transform (don't forget to return to GL_MODELVIEW after altering the projection!), and draws a red, lit teapot in the center of the screen. You should only need to make use of the OpenGL calls you learnt last semester. (Include glut to draw the teapot but don't use any other glut calls except for glutInit() in the main function. Also add -lglut to the makefile).

5. Add code to the event function. Start by recognising a keypress event, and quit the program when the escape key is pressed.

   You need to check the event->type member for equality with SDL_KEYDOWN, then check the value of event->key.keysym.sym (which will be a virtual keycode such as SDLK_ESCAPE. A full list is in the SDLKey man page).

6. Add code to the event function to control camera movement around the teapot. The best way to do this is to have several boolean flags that keep track of which keys are pressed, and each frame move the camera in the appropriate direction. You should be able to get fluid movement with the WSAD and arrow keys.

Extension activities:

7. Modify display so the framerate is displayed on-screen instead of on the terminal.
8. Write code in update so the camera moves at a constant speed, regardless of the framerate.