Qwt User's Guide
QwtDateScaleEngine Class Reference

A scale engine for date/time values. More...

#include <qwt_date_scale_engine.h>

Inheritance diagram for QwtDateScaleEngine:

Public Member Functions

 QwtDateScaleEngine (Qt::TimeSpec=Qt::LocalTime)
 Constructor.
virtual ~QwtDateScaleEngine ()
 Destructor.
void setTimeSpec (Qt::TimeSpec)
Qt::TimeSpec timeSpec () const
void setUtcOffset (int seconds)
int utcOffset () const
void setWeek0Type (QwtDate::Week0Type)
QwtDate::Week0Type week0Type () const
void setMaxWeeks (int)
int maxWeeks () const
virtual void autoScale (int maxNumSteps, double &x1, double &x2, double &stepSize) const
virtual QwtScaleDiv divideScale (double x1, double x2, int maxMajorSteps, int maxMinorSteps, double stepSize=0.0) const
 Calculate a scale division for a date/time interval.
virtual QwtDate::IntervalType intervalType (const QDateTime &, const QDateTime &, int maxSteps) const
QDateTime toDateTime (double) const

Protected Member Functions

virtual QDateTime alignDate (const QDateTime &, double stepSize, QwtDate::IntervalType, bool up) const

Detailed Description

A scale engine for date/time values.

QwtDateScaleEngine builds scales from a time intervals. Together with QwtDateScaleDraw it can be used for axes according to date/time values.

Years, months, weeks, days, hours and minutes are organized in steps with non constant intervals. QwtDateScaleEngine classifies intervals and aligns the boundaries and tick positions according to this classification.

QwtDateScaleEngine supports representations depending on Qt::TimeSpec specifications. The valid range for scales is limited by the range of QDateTime, that differs between Qt4 and Qt5.

Datetime values are expected as the number of milliseconds since 1970-01-01T00:00:00 Universal Coordinated Time - also known as "The Epoch", that can be converted to QDateTime using QwtDate::toDateTime().

See also:
QwtDate, QwtPlot::setAxisScaleEngine(), QwtAbstractScale::setScaleEngine()

Constructor & Destructor Documentation

QwtDateScaleEngine::QwtDateScaleEngine ( Qt::TimeSpec  timeSpec = Qt::LocalTime)

Constructor.

The engine is initialized to build scales for the given time specification. It classifies intervals > 4 weeks as >= Qt::Month. The first week of a year is defined like for QwtDate::FirstThursday.

Parameters:
timeSpecTime specification
See also:
setTimeSpec(), setMaxWeeks(), setWeek0Type()

Member Function Documentation

QDateTime QwtDateScaleEngine::alignDate ( const QDateTime &  dateTime,
double  stepSize,
QwtDate::IntervalType  intervalType,
bool  up 
) const [protected, virtual]

Align a date/time value for a step size

For Qt::Day alignments there is no "natural day 0" - instead the first day of the year is used to avoid jumping major ticks positions when panning a scale. For other alignments ( f.e according to the first day of the month ) alignDate() has to be overloaded.

Parameters:
dateTimeDate/time value
stepSizeStep size
intervalTypeInterval type
upWhen true dateTime is ceiled - otherwise it is floored
Returns:
Aligned date/time value
void QwtDateScaleEngine::autoScale ( int  maxNumSteps,
double &  x1,
double &  x2,
double &  stepSize 
) const [virtual]

Align and divide an interval

The algorithm aligns and divides the interval into steps.

Datetime interval divisions are usually not equidistant and the calculated stepSize can only be used as an approximation for the steps calculated by divideScale().

Parameters:
maxNumStepsMax. number of steps
x1First limit of the interval (In/Out)
x2Second limit of the interval (In/Out)
stepSizeStep size (Out)
See also:
QwtScaleEngine::setAttribute()

Reimplemented from QwtLinearScaleEngine.

QwtScaleDiv QwtDateScaleEngine::divideScale ( double  x1,
double  x2,
int  maxMajorSteps,
int  maxMinorSteps,
double  stepSize = 0.0 
) const [virtual]

Calculate a scale division for a date/time interval.

Parameters:
x1First interval limit
x2Second interval limit
maxMajorStepsMaximum for the number of major steps
maxMinorStepsMaximum number of minor steps
stepSizeStep size. If stepSize == 0, the scaleEngine calculates one.
Returns:
Calculated scale division

Reimplemented from QwtLinearScaleEngine.

QwtDate::IntervalType QwtDateScaleEngine::intervalType ( const QDateTime &  minDate,
const QDateTime &  maxDate,
int  maxSteps 
) const [virtual]

Classification of a date/time interval division

Parameters:
minDateMinimum ( = earlier ) of the interval
maxDateMaximum ( = later ) of the interval
maxStepsMaximum for the number of steps
Returns:
Interval classification
Returns:
Upper limit for the number of weeks, when an interval can be classified as Qt::Week.
See also:
setMaxWeeks(), week0Type()
void QwtDateScaleEngine::setMaxWeeks ( int  weeks)

Set a upper limit for the number of weeks, when an interval can be classified as Qt::Week.

The default setting is 4 weeks.

Parameters:
weeksUpper limit for the number of weeks
Note:
In business charts a year is often devided into weeks [1-52]
See also:
maxWeeks(), setWeek0Type()
void QwtDateScaleEngine::setTimeSpec ( Qt::TimeSpec  timeSpec)

Set the time specification used by the engine

Parameters:
timeSpecTime specification
See also:
timeSpec(), setUtcOffset(), toDateTime()
void QwtDateScaleEngine::setUtcOffset ( int  seconds)

Set the offset in seconds from Coordinated Universal Time

Parameters:
secondsOffset in seconds
Note:
The offset has no effect beside for the time specification Qt::OffsetFromUTC.
See also:
QDate::utcOffset(), setTimeSpec(), toDateTime()

Sets how to identify the first week of a year.

Parameters:
week0TypeMode how to identify the first week of a year
See also:
week0Type(), setMaxWeeks()
Note:
week0Type has no effect beside for intervals classified as QwtDate::Week.
Qt::TimeSpec QwtDateScaleEngine::timeSpec ( ) const
Returns:
Time specification used by the engine
See also:
setTimeSpec(), utcOffset(), toDateTime()
QDateTime QwtDateScaleEngine::toDateTime ( double  value) const

Translate a double value into a QDateTime object.

For QDateTime result is bounded by QwtDate::minDate() and QwtDate::maxDate()

Returns:
QDateTime object initialized with timeSpec() and utcOffset().
See also:
timeSpec(), utcOffset(), QwtDate::toDateTime()
Returns:
Offset in seconds from Coordinated Universal Time
Note:
The offset has no effect beside for the time specification Qt::OffsetFromUTC.
See also:
QDate::setUtcOffset(), setTimeSpec(), toDateTime()
Returns:
Setting how to identify the first week of a year.
See also:
setWeek0Type(), maxWeeks()

List of all members.

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