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author | Jiang Jiang <gzjjgod@gmail.com> |
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date | Wed, 01 Jul 2009 16:12:00 +0000 |
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<HTML ><HEAD ><TITLE >SDL_AddTimer</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ "><LINK REL="HOME" TITLE="SDL Library Documentation" HREF="index.html"><LINK REL="UP" TITLE="Time" HREF="time.html"><LINK REL="PREVIOUS" TITLE="SDL_Delay" HREF="sdldelay.html"><LINK REL="NEXT" TITLE="SDL_RemoveTimer" HREF="sdlremovetimer.html"></HEAD ><BODY CLASS="REFENTRY" BGCOLOR="#FFF8DC" TEXT="#000000" LINK="#0000ee" VLINK="#551a8b" ALINK="#ff0000" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >SDL Library Documentation</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="sdldelay.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="sdlremovetimer.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><H1 ><A NAME="SDLADDTIMER" ></A >SDL_AddTimer</H1 ><DIV CLASS="REFNAMEDIV" ><A NAME="AEN8482" ></A ><H2 >Name</H2 >SDL_AddTimer -- Add a timer which will call a callback after the specified number of milliseconds has elapsed.</DIV ><DIV CLASS="REFSYNOPSISDIV" ><A NAME="AEN8485" ></A ><H2 >Synopsis</H2 ><DIV CLASS="FUNCSYNOPSIS" ><A NAME="AEN8486" ></A ><P ></P ><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 ></P ></DIV ></DIV ><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 ><DIV CLASS="REFSECT1" ><A NAME="AEN8495" ></A ><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 ></DIV ><DIV CLASS="REFSECT1" ><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 ></P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="sdldelay.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="sdlremovetimer.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >SDL_Delay</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="time.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >SDL_RemoveTimer</TD ></TR ></TABLE ></DIV ></BODY ></HTML >