Function prototype for the timer callback function.
Defined in SDL_timer.h
typedef Uint32 (SDLCALL * SDL_TimerCallback) (Uint32 interval, void *param);
The callback function is passed the current timer interval and returns the next timer interval. If the returned value is the same as the one passed in, the periodic alarm continues, otherwise a new alarm is scheduled. If the callback returns 0, the periodic alarm is cancelled.