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GameTimer.cpp
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GameTimer.cpp
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//***************************************************************************************
// GameTimer.cpp by Frank Luna (C) 2011 All Rights Reserved.
//***************************************************************************************
#include <windows.h>
#include "GameTimer.h"
GameTimer::GameTimer()
: mSecondsPerCount(0.0), mDeltaTime(-1.0), mBaseTime(0),
mPausedTime(0), mPrevTime(0), mCurrTime(0), mStopped(false)
{
__int64 countsPerSec;
QueryPerformanceFrequency((LARGE_INTEGER*)&countsPerSec);
mSecondsPerCount = 1.0 / (double)countsPerSec;
}
// Returns the total time elapsed since Reset() was called, NOT counting any
// time when the clock is stopped.
float GameTimer::TotalTime()const
{
// If we are stopped, do not count the time that has passed since we stopped.
// Moreover, if we previously already had a pause, the distance
// mStopTime - mBaseTime includes paused time, which we do not want to count.
// To correct this, we can subtract the paused time from mStopTime:
//
// |<--paused time-->|
// ----*---------------*-----------------*------------*------------*------> time
// mBaseTime mStopTime startTime mStopTime mCurrTime
if( mStopped )
{
return (float)(((mStopTime - mPausedTime)-mBaseTime)*mSecondsPerCount);
}
// The distance mCurrTime - mBaseTime includes paused time,
// which we do not want to count. To correct this, we can subtract
// the paused time from mCurrTime:
//
// (mCurrTime - mPausedTime) - mBaseTime
//
// |<--paused time-->|
// ----*---------------*-----------------*------------*------> time
// mBaseTime mStopTime startTime mCurrTime
else
{
return (float)(((mCurrTime-mPausedTime)-mBaseTime)*mSecondsPerCount);
}
}
float GameTimer::DeltaTime()const
{
return (float)mDeltaTime;
}
void GameTimer::Reset()
{
__int64 currTime;
QueryPerformanceCounter((LARGE_INTEGER*)&currTime);
mBaseTime = currTime;
mPrevTime = currTime;
mStopTime = 0;
mStopped = false;
}
void GameTimer::Start()
{
__int64 startTime;
QueryPerformanceCounter((LARGE_INTEGER*)&startTime);
// Accumulate the time elapsed between stop and start pairs.
//
// |<-------d------->|
// ----*---------------*-----------------*------------> time
// mBaseTime mStopTime startTime
if( mStopped )
{
mPausedTime += (startTime - mStopTime);
mPrevTime = startTime;
mStopTime = 0;
mStopped = false;
}
}
void GameTimer::Stop()
{
if( !mStopped )
{
__int64 currTime;
QueryPerformanceCounter((LARGE_INTEGER*)&currTime);
mStopTime = currTime;
mStopped = true;
}
}
void GameTimer::Tick()
{
if( mStopped )
{
mDeltaTime = 0.0;
return;
}
__int64 currTime;
QueryPerformanceCounter((LARGE_INTEGER*)&currTime);
mCurrTime = currTime;
// Time difference between this frame and the previous.
mDeltaTime = (mCurrTime - mPrevTime)*mSecondsPerCount;
// Prepare for next frame.
mPrevTime = mCurrTime;
// Force nonnegative. The DXSDK's CDXUTTimer mentions that if the
// processor goes into a power save mode or we get shuffled to another
// processor, then mDeltaTime can be negative.
if(mDeltaTime < 0.0)
{
mDeltaTime = 0.0;
}
}