Game Engine Architecture

323

public:

// Call this when the game first starts up.

static void init()

{

s_cyclesPerSecond

= (F32)readHiResTimerFrequency();

}

// Construct a clock.

explicit Clock(F32startTimeSeconds = 0.0f) :

m_timeCycles( secondsToCycles(startTimeSeconds)),

m_timeScale( 1.0f), // default to unscaled

m_isPaused( false) // default to running

{

}

// Return the current time in cycles. NOTE that we do

// not return absolute time measurements in floating

// point seconds, because a 32-bit float doesn’t have

// enough precision. See calcDeltaSeconds().

U64 getTimeCycles() const

{

return m_timeCycles;

}

// Determine the difference between this clock’s

// absolute time and that of another clock, in

// seconds. We only return time deltas as floating

// point seconds, due to the precision limitations of

// a 32-bit float.

F32 calcDeltaSeconds(const Clock& other)

{

U64 dt = m_timeCycles – other.m_timeCycles;

return cyclesToSeconds(dt);

}

// This function should be called once per frame,

// with the real measured frame time delta in seconds.

void update(F32 dtRealSeconds)

{

if (!m_isPaused)

{

U64 dtScaledCycles

= secondsToCycles(

dtRealSeconds * m_timeScale);

m_timeCycles += dtScaledCycles;

}

}

7.5. Measuring and Dealing with Time