CTIMER类-无论机器运行速度如何，都能保持恒定的频率

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#integer #timer #float #windows #class #null

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本文介绍了一个用于游戏开发中的计时器类CTimer，该类可以确保在不同的机器运行速度下保持恒定的帧率(FPS)。通过使用Windows API的QueryPerformanceCounter和QueryPerformanceFrequency函数来获取高精度的时间戳，从而实现精确的时间测量。

无论机器运行速度如何，都能保持恒定的频率

CTIMER.CPP

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#include "CTimer.h"

//---------------------- default constructor------------------------------
//
//-------------------------------------------------------------------------
CTimer::CTimer(): m_FPS(0),
             m_TimeElapsed(0.0f),
             m_FrameTime(0),
             m_LastTime(0),
             m_PerfCountFreq(0)
{
//how many ticks per sec do we get
QueryPerformanceFrequency( (LARGE_INTEGER*)&m_PerfCountFreq);

m_TimeScale = 1.0f/m_PerfCountFreq;
}

//---------------------- constructor-------------------------------------
//
// use to specify FPS
//
//-------------------------------------------------------------------------
CTimer::CTimer(float fps): m_FPS(fps),
                    m_TimeElapsed(0.0f),
                    m_LastTime(0),
                    m_PerfCountFreq(0)
{

//how many ticks per sec do weget
QueryPerformanceFrequency( (LARGE_INTEGER*)&m_PerfCountFreq);

m_TimeScale =1.0f/m_PerfCountFreq;

//calculate ticks perframe
m_FrameTime = (LONGLONG)(m_PerfCountFreq /m_FPS);
}

//------------------------Start()-----------------------------------------
//
// call this immediately prior to game loop.Starts the timer (obviously!)
//
//--------------------------------------------------------------------------
void CTimer::Start()
{
//get the time
QueryPerformanceCounter( (LARGE_INTEGER*)&m_LastTime);

//update time to render next frame
m_NextTime = m_LastTime + m_FrameTime;

return;
}

//-------------------------ReadyForNextFrame()-------------------------------
//
// returns true if it is time to move on to thenext frame step. To be used if
// FPS is set.
//
//----------------------------------------------------------------------------
bool CTimer::ReadyForNextFrame()
{
if (!m_FPS)
{
MessageBox(NULL, "No FPS set in timer", "Doh!", 0);

returnfalse;
}

QueryPerformanceCounter( (LARGE_INTEGER*)&m_CurrentTime);

if (m_CurrentTime >m_NextTime)
{

m_TimeElapsed =(m_CurrentTime - m_LastTime) * m_TimeScale;
m_LastTime =m_CurrentTime;

//update time to render nextframe
m_NextTime = m_CurrentTime +m_FrameTime;

return true;
}

return false;
}

//--------------------------- TimeElapsed--------------------------------
//
// returns time elapsed since last call to thisfunction. Use in main
// when calculations are to be based on dt.
//
//-------------------------------------------------------------------------
double CTimer::TimeElapsed()
{
QueryPerformanceCounter( (LARGE_INTEGER*)&m_CurrentTime);

m_TimeElapsed = (m_CurrentTime -m_LastTime) * m_TimeScale;

m_LastTime =m_CurrentTime;

return m_TimeElapsed;

}

CTIMER.H

----------------

#ifndef CTIMER_H
#define CTIMER_H
//-----------------------------------------------------------------------
//
// Name: CTimer.h
//
// Author: Mat Buckland 2002
//
// Desc: Windows timer class for the book GameAI
// Programming with Neural Nets and GeneticAlgorithms.
//
//-----------------------------------------------------------------------

#include<windows.h>

class CTimer
{

private:

LONGLONG m_CurrentTime,
          m_LastTime,
       m_NextTime,
       m_FrameTime,
       m_PerfCountFreq;

double m_TimeElapsed,
m_TimeScale;

float m_FPS;

public:

//ctors
CTimer();
CTimer(float fps);

//whatdayaknow, this starts the timer
void Start();

//determines if enough time has passed to moveonto next frame
bool ReadyForNextFrame();

//only use this after a call to theabove.
double GetTimeElapsed(){returnm_TimeElapsed;}

double TimeElapsed();