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SDL_AddTimer

Use this function to set up a callback function to be run on a separate thread after the specified number of milliseconds has elapsed.

Syntax

SDL_TimerID SDL_AddTimer(Uint32            interval,
                         SDL_TimerCallback callback,
                         void*             param)

Function Parameters

interval

the timer delay (ms) passed to callback

callback

the function to call when the specified interval elapses; see Remarks for details

param

a pointer that is passed to callback

Return Value

Returns a timer ID or 0 if an error occurs; call SDL_GetError() for more information.

Code Examples

/* Start the timer; the callback below will be executed after the delay */

Uint32 delay = (33 / 10) * 10;  /* To round it down to the nearest 10 ms */
SDL_TimerID my_timer_id = SDL_AddTimer(delay, my_callbackfunc, my_callback_param);

...

Uint32 my_callbackfunc(Uint32 interval, void *param)
{
    SDL_Event event;
    SDL_UserEvent userevent;

    /* In this example, our callback pushes an SDL_USEREVENT event
    into the queue, and causes our callback to be called again at the
    same interval: */

    userevent.type = SDL_USEREVENT;
    userevent.code = 0;
    userevent.data1 = NULL;
    userevent.data2 = NULL;

    event.type = SDL_USEREVENT;
    event.user = userevent;

    SDL_PushEvent(&event);
    return(interval);
}

Note that it is possible to avoid the multithreading problems with SDL timers by giving to userevent.data1 the address of a function you want to be executed and to userevent.data2 its params, and then deal with it in the event loop.

/* with the same code as before: */
Uint32 my_callbackfunc(Uint32 interval, void *param)
{
    SDL_Event event;
    SDL_UserEvent userevent;

    /* In this example, our callback pushes a function
    into the queue, and causes our callback to be called again at the
    same interval: */

    userevent.type = SDL_USEREVENT;
    userevent.code = 0;
    userevent.data1 = &my_function;
    userevent.data2 = param;

    event.type = SDL_USEREVENT;
    event.user = userevent;

    SDL_PushEvent(&event);
    return(interval);
}

/* Now the event loop */
SDL_Event event;
while (SDL_PollEvent (&event))
{
    switch(event.type)
    {
        case SDL_USEREVENT: {
            /* and now we can call the function we wanted to call in the timer but couldn't because of the multithreading problems */
            void (*p) (void*) = event.user.data1;
            p(event.user.data2);
            break;
        }
        /* ... */
    }
}

Remarks

If you use this function, you must pass SDL_INIT_TIMER to SDL_Init().

The callback function is passed the current timer interval and the user supplied parameter from the SDL_AddTimer() call and should return the next timer interval. If the value returned from the callback is 0, the timer is canceled.

The callback is run on a separate thread. See the code examples for a method of processing the timer callbacks on the main thread if that's desired.

Timers take into account the amount of time it took to execute the callback. For example, if the callback took 250 ms to execute and returned 1000 (ms), the timer would only wait another 750 ms before its next iteration.


CategoryAPI, CategoryTimer

None: SDL_AddTimer (last edited 2019-12-23 18:01:33 by ProgramGamer)

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