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POLimiting Update Rate in C++. Why does this code update once a second not 60 times a second?
 

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  1. POLimiting Update Rate in C++. Why does this code update once a second not 60 times a second?
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    <p>I am making a small game with C++ OpenGL. <code>update()</code> is normally called once every time the program runs through the code. I am trying to limit this to 60 times per second (I want the game to update at the same speed on different speed computers). </p> <p>The code included below runs a timer and should call <code>update()</code> once the timer is >= than 0.0166666666666667 (60 times per second). However the statement <code>if((seconds - lastTime) &gt;= 0.0166666666666667)</code> seems only to be tripped once per second. Does anyone know why?</p> <p>Thanks in advance for your help. </p> <pre><code>//Global Timer variables double secondsS; double lastTime; time_t timer; struct tm y2k; double seconds; void init() { glClearColor(0,0,0,0.0); // Sets the clear colour to white. // glClear(GL_COLOR_BUFFER_BIT) in the display function //Init viewport viewportX = 0; viewportY = 0; initShips(); //Time lastTime = 0; time_t timerS; struct tm y2k; y2k.tm_hour = 0; y2k.tm_min = 0; y2k.tm_sec = 0; y2k.tm_year = 100; y2k.tm_mon = 0; y2k.tm_mday = 1; time(&amp;timerS); /* get current time; same as: timer = time(NULL) */ secondsS = difftime(timerS,mktime(&amp;y2k)); printf ("%.f seconds since January 1, 2000 in the current timezone \n", secondsS); loadTextures(); ShowCursor(true); glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA); } void timeKeeper() { y2k.tm_hour = 0; y2k.tm_min = 0; y2k.tm_sec = 0; y2k.tm_year = 100; y2k.tm_mon = 0; y2k.tm_mday = 1; time(&amp;timer); /* get current time; same as: timer = time(NULL) */ seconds = difftime(timer,mktime(&amp;y2k)); seconds -= secondsS; //Run 60 times a second. This limits updates to a constant standard. if((seconds - lastTime) &gt;= 0.0166666666666667) { lastTime = seconds; update(); //printf ("%.f seconds since beginning program \n", seconds); } } </code></pre> <p><code>timeKeeper()</code> is called in int <code>WINAPI WinMain</code>, while the program is <code>!done</code></p> <p>EDIT:</p> <p>Thanks to those who helped, you pointed me on the right track. As mentioned in the answer below <code>&lt;ctime&gt;</code> does not have ms accuracy. I have therefore implemented the following code that has the correct accuracy:</p> <pre><code>double GetSystemTimeSample() { FILETIME ft1, ft2; // assume little endian and that ULONGLONG has same alignment as FILETIME ULONGLONG &amp;t1 = *reinterpret_cast&lt;ULONGLONG*&gt;(&amp;ft1), &amp;t2 = *reinterpret_cast&lt;ULONGLONG*&gt;(&amp;ft2); GetSystemTimeAsFileTime(&amp;ft1); do { GetSystemTimeAsFileTime(&amp;ft2); } while (t1 == t2); return (t2 - t1) / 10000.0; }//GetSystemTimeSample void timeKeeper() { thisTime += GetSystemTimeSample(); cout &lt;&lt; thisTime &lt;&lt; endl; //Run 60 times a second. This limits updates to a constant standard. if(thisTime &gt;= 16.666666666666699825) //Compare to a value in milliseconds { thisTime = seconds; update(); } } </code></pre>
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