1 <HTML 2 ><HEAD 3 ><TITLE 4 >SDL_AddTimer</TITLE 5 ><META 6 NAME="GENERATOR" 7 CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ 8 "><LINK 9 REL="HOME" 10 TITLE="SDL Library Documentation" 11 HREF="index.html"><LINK 12 REL="UP" 13 TITLE="Time" 14 HREF="time.html"><LINK 15 REL="PREVIOUS" 16 TITLE="SDL_Delay" 17 HREF="sdldelay.html"><LINK 18 REL="NEXT" 19 TITLE="SDL_RemoveTimer" 20 HREF="sdlremovetimer.html"></HEAD 21 ><BODY 22 CLASS="REFENTRY" 23 BGCOLOR="#FFF8DC" 24 TEXT="#000000" 25 LINK="#0000ee" 26 VLINK="#551a8b" 27 ALINK="#ff0000" 28 ><DIV 29 CLASS="NAVHEADER" 30 ><TABLE 31 SUMMARY="Header navigation table" 32 WIDTH="100%" 33 BORDER="0" 34 CELLPADDING="0" 35 CELLSPACING="0" 36 ><TR 37 ><TH 38 COLSPAN="3" 39 ALIGN="center" 40 >SDL Library Documentation</TH 41 ></TR 42 ><TR 43 ><TD 44 WIDTH="10%" 45 ALIGN="left" 46 VALIGN="bottom" 47 ><A 48 HREF="sdldelay.html" 49 ACCESSKEY="P" 50 >Prev</A 51 ></TD 52 ><TD 53 WIDTH="80%" 54 ALIGN="center" 55 VALIGN="bottom" 56 ></TD 57 ><TD 58 WIDTH="10%" 59 ALIGN="right" 60 VALIGN="bottom" 61 ><A 62 HREF="sdlremovetimer.html" 63 ACCESSKEY="N" 64 >Next</A 65 ></TD 66 ></TR 67 ></TABLE 68 ><HR 69 ALIGN="LEFT" 70 WIDTH="100%"></DIV 71 ><H1 72 ><A 73 NAME="SDLADDTIMER" 74 ></A 75 >SDL_AddTimer</H1 76 ><DIV 77 CLASS="REFNAMEDIV" 78 ><A 79 NAME="AEN8482" 80 ></A 81 ><H2 82 >Name</H2 83 >SDL_AddTimer -- Add a timer which will call a callback after the specified number of milliseconds has 84 elapsed.</DIV 85 ><DIV 86 CLASS="REFSYNOPSISDIV" 87 ><A 88 NAME="AEN8485" 89 ></A 90 ><H2 91 >Synopsis</H2 92 ><DIV 93 CLASS="FUNCSYNOPSIS" 94 ><A 95 NAME="AEN8486" 96 ></A 97 ><P 98 ></P 99 ><PRE 100 CLASS="FUNCSYNOPSISINFO" 101 >#include "SDL.h"</PRE 102 ><P 103 ><CODE 104 ><CODE 105 CLASS="FUNCDEF" 106 >SDL_TimerID <B 107 CLASS="FSFUNC" 108 >SDL_AddTimer</B 109 ></CODE 110 >(Uint32 interval, SDL_NewTimerCallback callback, void *param);</CODE 111 ></P 112 ><P 113 ></P 114 ></DIV 115 ></DIV 116 ><DIV 117 CLASS="REFSECT1" 118 ><A 119 NAME="SDLNEWTIMERCALLBACK" 120 ></A 121 ><H2 122 >Callback</H2 123 ><PRE 124 CLASS="PROGRAMLISTING" 125 >/* type definition for the "new" timer callback function */ 126 typedef Uint32 (*SDL_NewTimerCallback)(Uint32 interval, void *param);</PRE 127 ></DIV 128 ><DIV 129 CLASS="REFSECT1" 130 ><A 131 NAME="AEN8495" 132 ></A 133 ><H2 134 >Description</H2 135 ><P 136 >Adds a callback function to be run after the specified number of 137 milliseconds has elapsed. The callback function is passed the current 138 timer interval and the user supplied parameter from the 139 <TT 140 CLASS="FUNCTION" 141 >SDL_AddTimer</TT 142 > call and returns the next timer 143 interval. If the returned value from the callback is the same as the one 144 passed in, the periodic alarm continues, otherwise a new alarm is 145 scheduled.</P 146 ><P 147 >To cancel a currently running timer call 148 <A 149 HREF="sdlremovetimer.html" 150 >SDL_RemoveTimer</A 151 > with the 152 timer ID returned from 153 <TT 154 CLASS="FUNCTION" 155 >SDL_AddTimer</TT 156 >.</P 157 ><P 158 >The timer callback function may run in a different thread than your 159 main program, and so shouldn't call any functions from within itself. 160 You may always call <A 161 HREF="sdlpushevent.html" 162 >SDL_PushEvent</A 163 >, however.</P 164 ><P 165 >The granularity of the timer is platform-dependent, but you should count 166 on it being at least 10 ms as this is the most common number. 167 This means that if 168 you request a 16 ms timer, your callback will run approximately 20 ms 169 later on an unloaded system. If you wanted to set a flag signaling 170 a frame update at 30 frames per second (every 33 ms), you might set a 171 timer for 30 ms (see example below). 172 173 If you use this function, you need to pass <TT 174 CLASS="LITERAL" 175 >SDL_INIT_TIMER</TT 176 > 177 to <A 178 HREF="sdlinit.html" 179 >SDL_Init</A 180 >.</P 181 ></DIV 182 ><DIV 183 CLASS="REFSECT1" 184 ><A 185 NAME="AEN8507" 186 ></A 187 ><H2 188 >Return Value</H2 189 ><P 190 >Returns an ID value for the added timer or 191 <SPAN 192 CLASS="RETURNVALUE" 193 >NULL</SPAN 194 > if there was an error.</P 195 ></DIV 196 ><DIV 197 CLASS="REFSECT1" 198 ><A 199 NAME="AEN8511" 200 ></A 201 ><H2 202 >Examples</H2 203 ><P 204 ><PRE 205 CLASS="PROGRAMLISTING" 206 >my_timer_id = SDL_AddTimer((33/10)*10, my_callbackfunc, my_callback_param);</PRE 207 ></P 208 ></DIV 209 ><DIV 210 CLASS="REFSECT1" 211 ><A 212 NAME="AEN8515" 213 ></A 214 ><H2 215 >See Also</H2 216 ><P 217 ><A 218 HREF="sdlremovetimer.html" 219 ><TT 220 CLASS="FUNCTION" 221 >SDL_RemoveTimer</TT 222 ></A 223 >, 224 <A 225 HREF="sdlpushevent.html" 226 ><TT 227 CLASS="FUNCTION" 228 >SDL_PushEvent</TT 229 ></A 230 ></P 231 ></DIV 232 ><DIV 233 CLASS="NAVFOOTER" 234 ><HR 235 ALIGN="LEFT" 236 WIDTH="100%"><TABLE 237 SUMMARY="Footer navigation table" 238 WIDTH="100%" 239 BORDER="0" 240 CELLPADDING="0" 241 CELLSPACING="0" 242 ><TR 243 ><TD 244 WIDTH="33%" 245 ALIGN="left" 246 VALIGN="top" 247 ><A 248 HREF="sdldelay.html" 249 ACCESSKEY="P" 250 >Prev</A 251 ></TD 252 ><TD 253 WIDTH="34%" 254 ALIGN="center" 255 VALIGN="top" 256 ><A 257 HREF="index.html" 258 ACCESSKEY="H" 259 >Home</A 260 ></TD 261 ><TD 262 WIDTH="33%" 263 ALIGN="right" 264 VALIGN="top" 265 ><A 266 HREF="sdlremovetimer.html" 267 ACCESSKEY="N" 268 >Next</A 269 ></TD 270 ></TR 271 ><TR 272 ><TD 273 WIDTH="33%" 274 ALIGN="left" 275 VALIGN="top" 276 >SDL_Delay</TD 277 ><TD 278 WIDTH="34%" 279 ALIGN="center" 280 VALIGN="top" 281 ><A 282 HREF="time.html" 283 ACCESSKEY="U" 284 >Up</A 285 ></TD 286 ><TD 287 WIDTH="33%" 288 ALIGN="right" 289 VALIGN="top" 290 >SDL_RemoveTimer</TD 291 ></TR 292 ></TABLE 293 ></DIV 294 ></BODY 295 ></HTML 296 >
