www.pudn.com > chapter01.zip > HiResTimer.h

/**************************************************************************** 
 HiResTimer.h 
  
 Wrapper for the high-resolution timer. Can't be used if the hi-res timer 
 doesn't exist. 
   
 Author   :   Dave Astle 
 Date     :   2/1/2001 
 
 Written for OpenGL Game Programming 
*****************************************************************************/ 
 
#ifndef __TIMER_H_INCLUDED__ 
#define __TIMER_H_INCLUDED__ 
 
#include  
 
 
class CHiResTimer 
{ 
public: 
  CHiResTimer() {} 
  ~CHiResTimer() {} 
 
/***************************************************************************** 
 Init() 
 
 If the hi-res timer is present, the tick rate is stored and the function 
 returns true. Otherwise, the function returns false, and the timer should 
 not be used. 
*****************************************************************************/ 
bool Init() 
{ 
  if (!QueryPerformanceFrequency(&m_ticksPerSecond)) 
  { 
    // system doesn't support hi-res timer 
    return false; 
  } 
  else 
  { 
    QueryPerformanceCounter(&m_startTime); 
    return true; 
  } 
} // end Init() 
 
 
float GetElapsedSeconds(unsigned long elapsedFrames = 1) 
{ 
  static LARGE_INTEGER s_lastTime = m_startTime; 
  LARGE_INTEGER currentTime; 
 
  QueryPerformanceCounter(¤tTime); 
 
  float seconds =  ((float)currentTime.QuadPart - (float)s_lastTime.QuadPart) / (float)m_ticksPerSecond.QuadPart; 
 
  // reset the timer 
  s_lastTime = currentTime; 
 
  return seconds; 
} // end GetElapsedSeconds() 
 
 
/*************************************************************************** 
 GetFPS() 
 
 Returns the average frames per second over elapsedFrames, which defaults to 
 one. If this is not called every frame, the client should track the number 
 of frames itself, and reset the value after this is called. 
***************************************************************************/ 
float GetFPS(unsigned long elapsedFrames = 1) 
{ 
  static LARGE_INTEGER s_lastTime = m_startTime; 
  LARGE_INTEGER currentTime; 
 
  m_totalFrames += elapsedFrames; 
 
  QueryPerformanceCounter(¤tTime); 
 
  float fps = (float)elapsedFrames * (float)m_ticksPerSecond.QuadPart / ((float)currentTime.QuadPart - (float)s_lastTime.QuadPart); 
 
  // reset the timer 
  s_lastTime = currentTime; 
 
  return fps; 
} // end GetFPS 
 
 
/*************************************************************************** 
 GetAggregateFPS() 
 
 Returns the average fps since the last time Reset() was called. Note that 
 this is meant to be used in conjunction with LockFPS or GetFPS. Otherwise, 
 the function has no way of knowing how many frames have actually elapsed. 
***************************************************************************/ 
float GetAggregateFPS() 
{ 
  LARGE_INTEGER currentTime; 
 
  QueryPerformanceCounter(¤tTime); 
 
  return ((float) m_totalFrames * (float)m_ticksPerSecond.QuadPart / ((float)currentTime.QuadPart - (float)m_startTime.QuadPart)); 
} // end GetAggregateFPS() 
 
 
/*************************************************************************** 
 LockFPS() 
 
 Used to lock the frame rate to a set amount. This will block until enough 
 time has passed to ensure that the fps won't go over the requested amount. 
 Note that this can only keep the fps from going above the specified level; 
 it can still drop below it. It is assumed that if used, this function will 
 be called every frame. The value returned is the instantaneous fps, which 
 will be <= targetFPS. 
***************************************************************************/ 
float LockFPS(unsigned char targetFPS) 
{ 
  if (targetFPS == 0) 
    targetFPS = 1; 
 
  m_totalFrames++; 
 
  static LARGE_INTEGER s_lastTime = m_startTime; 
  LARGE_INTEGER currentTime; 
  float   fps; 
 
  // delay to maintain a constant frame rate 
  do { 
    QueryPerformanceCounter(¤tTime); 
    fps = (float)m_ticksPerSecond.QuadPart/((float)(currentTime.QuadPart - s_lastTime.QuadPart)); 
  } while (fps > (float)targetFPS); 
 
  // reset the timer 
  s_lastTime = m_startTime; 
 
  return fps; 
} // end LockFPS() 
 
 
private: 
  LARGE_INTEGER   m_startTime; 
  LARGE_INTEGER   m_ticksPerSecond; 
  unsigned long   m_totalFrames; 
}; 
 
#endif // __TIMER_H_INCLUDED_