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><H1
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>SDL_AddTimer</H1
><DIV
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><A
NAME="AEN8482"
></A
><H2
>Name</H2
>SDL_AddTimer&nbsp;--&nbsp;Add a timer which will call a callback after the specified number of milliseconds has
elapsed.</DIV
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><H2
>Synopsis</H2
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><P
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><PRE
CLASS="FUNCSYNOPSISINFO"
>#include "SDL.h"</PRE
><P
><CODE
><CODE
CLASS="FUNCDEF"
>SDL_TimerID <B
CLASS="FSFUNC"
>SDL_AddTimer</B
></CODE
>(Uint32 interval, SDL_NewTimerCallback callback, void *param);</CODE
></P
><P
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><DIV
CLASS="REFSECT1"
><A
NAME="SDLNEWTIMERCALLBACK"
></A
><H2
>Callback</H2
><PRE
CLASS="PROGRAMLISTING"
>/* type definition for the "new" timer callback function */
typedef Uint32 (*SDL_NewTimerCallback)(Uint32 interval, void *param);</PRE
></DIV
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CLASS="REFSECT1"
><A
NAME="AEN8495"
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><H2
>Description</H2
><P
>Adds a callback function to be run after the specified number of
milliseconds has elapsed. The callback function is passed the current
timer interval and the user supplied parameter from the
<TT
CLASS="FUNCTION"
>SDL_AddTimer</TT
> call and returns the next timer
interval. If the returned value from the callback is the same as the one
passed in, the periodic alarm continues, otherwise a new alarm is
scheduled.</P
><P
>To cancel a currently running timer call
<A
HREF="sdlremovetimer.html"
>SDL_RemoveTimer</A
> with the
timer ID returned from
<TT
CLASS="FUNCTION"
>SDL_AddTimer</TT
>.</P
><P
>The timer callback function may run in a different thread than your
main program, and so shouldn't call any functions from within itself.
You may always call <A
HREF="sdlpushevent.html"
>SDL_PushEvent</A
>, however.</P
><P
>The granularity of the timer is platform-dependent, but you should count
on it being at least 10 ms as this is the most common number.
This means that if
you request a 16 ms timer, your callback will run approximately 20 ms
later on an unloaded system.  If you wanted to set a flag signaling
a frame update at 30 frames per second (every 33 ms), you might set a
timer for 30 ms (see example below).

If you use this function, you need to pass <TT
CLASS="LITERAL"
>SDL_INIT_TIMER</TT
>
to <A
HREF="sdlinit.html"
>SDL_Init</A
>.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN8507"
></A
><H2
>Return Value</H2
><P
>Returns an ID value for the added timer or
<SPAN
CLASS="RETURNVALUE"
>NULL</SPAN
> if there was an error.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN8511"
></A
><H2
>Examples</H2
><P
><PRE
CLASS="PROGRAMLISTING"
>my_timer_id = SDL_AddTimer((33/10)*10, my_callbackfunc, my_callback_param);</PRE
></P
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><A
NAME="AEN8515"
></A
><H2
>See Also</H2
><P
><A
HREF="sdlremovetimer.html"
><TT
CLASS="FUNCTION"
>SDL_RemoveTimer</TT
></A
>,
<A
HREF="sdlpushevent.html"
><TT
CLASS="FUNCTION"
>SDL_PushEvent</TT
></A
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author	Ryan C. Gordon <icculus@icculus.org>
date	Mon, 21 Sep 2009 06:08:23 +0000
parents	355632dca928
children