Sage::CTimer Class Reference

The timer class. More...

#include <SageTimer.h>

Inheritance diagram for Sage::CTimer:

Collaboration diagram for Sage::CTimer:

Public Member Functions
	CTimer ()
	Constructor.
template<typename t >
void	Tick (const t &)
	One tick per frame.
const float	GetFrameTime () const
	Get time in seconds since last Tick.
const float	GetTime () const
	Get current time in seconds.
const uint32_t	GetFrameCount () const
	Get total number of frames since start of the program.
const uint32_t	GetFPS () const
	Get the current framerate.
void	SetFixedTimeStep (bool=true)
	Set fixed or variable timestep mode.
void	SetFrameTime (double)
	Set desired seconds per frame.

Protected Member Functions
void	ResetElapsedTime ()
	Reset elapsed time in fixed timestep mode.
template<typename t >
void	FixedTimeStepTick (const t &)
	One time tick in fixed timestep mode.
template<typename t >
void	VariableTimeStepTick (const t &)
	One time tick in variable timestep mode.

Static Protected Member Functions
static double	TicksToSeconds (uint64_t)
	Convert ticks to seconds.
static uint64_t	SecondsToTicks (double)
	Convert seconds to ticks.

Protected Attributes
LARGE_INTEGER	m_qpcFrequency = {0}
	Performance counter frequency in QPC units.
LARGE_INTEGER	m_qpcLastTime = {0}
	Performance counter time in QPC units.
uint64_t	m_qpcMaxDelta = 0
	Performance counter maximum time interval in QPC units.
uint64_t	m_qpcSecondCounter = 0
	Performance counter second counter in QPC units.
uint64_t	m_nElapsedTicks = 0
	Elapsed ticks in current frame.
uint64_t	m_nTotalTicks = 0
	Total ticks since program started.
uint64_t	m_nLeftOverTicks = 0
	For fixed timestep calculations.
uint32_t	m_nFrameCount = 0
	Total number of frames.
uint32_t	m_nFramesPerSec = 0
	Number of frames per second.
uint32_t	m_nFramesThisSec = 0
	Number of frames so far in current second.
bool	m_bFixedTimeStep = false
	Whether in fixed timestep mode.
uint64_t	m_nTargetTicks = 0
	Desired ticks per frame (fixed timestep mode).
uint64_t	m_nTimeDelta = 0
	Local variable for time interval.

Static Private Attributes
static const uint64_t	m_nTicksPerSec = 10000000
	Integer format represents time using 10,000,000 ticks per second.

Additional Inherited Members
Static Protected Attributes inherited from Sage::CWindowDesc
static HWND	m_Hwnd = 0
	Window handle.
static HINSTANCE	m_hInst = 0
	Instance handle.
static bool	m_bExitSizeMove = true
	User just finished moving/resizing window.

Detailed Description

The timer class allows you to measure frame time and total time. It has a Tick function that you should call once per frame with the code that you want executed once per frame as a parameter. The timer can be set into fixed timestep mode in which the frame time reported is always fixed. This is important in physics games since locking to the monitor frame rate is bound to give you unequal frame times because monitor frequency is almost always not what you expect. For example, a monitor advertized at 60Hz (which Windows will report is 60Hz) may actually be 59.3Hz.

Member Function Documentation

FixedTimeStepTick()

template<typename t >

void Sage::CTimer::FixedTimeStepTick ( const t & update )

protected

Process one time tick, fixed rate. If the app is running very close to the target elapsed time (within 1/4 of a millisecond) just clamp the clock to exactly match the target value. This prevents tiny and irrelevant errors from accumulating over time. Without this clamping, a game that requested a 60 fps fixed update, running with vsync enabled on a 59.94 NTSC display, would eventually accumulate enough tiny errors that it would drop a frame. It is better to just round small deviations down to zero to leave things running smoothly.

Parameters

update

Function to be called once per tick.

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GetFPS()

const uint32_t CTimer::GetFPS

(

)

const

Get the current frame rate.

Returns

Frame rate in frames per second.

GetFrameCount()

const uint32_t CTimer::GetFrameCount

(

)

const

Get total number of times Tick() has been called since the game started. Ideally this is the number of frames rendered, assuming that Tick() is called one per frame.

Returns

Frame count.

GetFrameTime()

const float CTimer::GetFrameTime

(

)

const

Get number of seconds that have elapsed since the last time Tick() was called. Ideally this is the last frame time, assuming that Tick() is called one per frame.

Returns

Elapsed seconds since last frame.

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GetTime()

const float CTimer::GetTime

(

)

const

Get number of seconds since the game started.

Returns

Total seconds since game started.

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ResetElapsedTime()

void CTimer::ResetElapsedTime ( )

protected

After an intentional timing discontinuity (for instance a blocking IO operation), call this to avoid having the fixed timestep logic attempt a set of catch-up Updat()e calls.

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SecondsToTicks()

uint64_t CTimer::SecondsToTicks ( double seconds )

staticprotected

Convert seconds into ticks, the unit used by the Windows performance counter.

Parameters

seconds

The number of seconds.

Returns

The corresponding number of ticks.

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SetFixedTimeStep()

void CTimer::SetFixedTimeStep

(

bool

isFixedTimestep = true

)

Set whether to use fixed or variable timestep mode.

Parameters

isFixedTimestep

true for fixed time step.

SetFrameTime()

void CTimer::SetFrameTime

(

double

targetElapsed

)

Set target frame time for fixed time step mode.

Parameters

targetElapsed

Target frame time in seconds.

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Tick()

template<typename t >

void Sage::CTimer::Tick

(

const t &

update

)

Process one time tick, either fixed or variable rate.

Parameters

update

Code to be called once per tick.

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TicksToSeconds()

double CTimer::TicksToSeconds ( uint64_t ticks )

staticprotected

Convert ticks, the unit used by the performance counter, into seconds.

Parameters

ticks

The number of ticks.

Returns

The corresponding number of seconds.

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VariableTimeStepTick()

template<typename t >

void Sage::CTimer::VariableTimeStepTick ( const t & update )

protected

Process one time tick, variable rate.

Parameters

update

Function to be called once per tick.

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