--- name: "QwtDateScaleEngine" section: "3" platform: "linux" package: "libqwt-doc" version: "6.1.4-2" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/QwtDateScaleEngine" --- # QwtDateScaleEngine(3) A scale engine for date/time values. ## NAME QwtDateScaleEngine - A scale engine for date/time values. ## SYNOPSIS `#include ` Inherits **QwtLinearScaleEngine**. ### 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\ ### Additional Inherited Members ## 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:** *timeSpec* Time 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:** *dateTime* Date/time value \ *stepSize* Step size \ *intervalType* Interval type \ *up* When 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:** *maxNumSteps* Max. number of steps \ *x1* First limit of the interval (In/Out) \ *x2* Second limit of the interval (In/Out) \ *stepSize* Step 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:** *x1* First interval limit \ *x2* Second interval limit \ *maxMajorSteps* Maximum for the number of major steps \ *maxMinorSteps* Maximum number of minor steps \ *stepSize* Step 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:** *minDate* Minimum ( = earlier ) of the interval \ *maxDate* Maximum ( = later ) of the interval \ *maxSteps* Maximum for the number of steps **Returns:** Interval classification ### int QwtDateScaleEngine::maxWeeks () const **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:** *weeks* Upper limit for the number of weeks **Note:** In business charts a year is often divided into weeks \[1-52\] **See also:** **maxWeeks()**, **setWeek0Type()** ### void QwtDateScaleEngine::setTimeSpec (Qt::TimeSpec timeSpec) Set the time specification used by the engine **Parameters:** *timeSpec* Time specification **See also:** **timeSpec()**, **setUtcOffset()**, **toDateTime()** ### void QwtDateScaleEngine::setUtcOffset (int seconds) Set the offset in seconds from Coordinated Universal Time **Parameters:** *seconds* Offset in seconds **Note:** The offset has no effect beside for the time specification Qt::OffsetFromUTC. **See also:** QDate::utcOffset(), **setTimeSpec()**, **toDateTime()** ### void QwtDateScaleEngine::setWeek0Type (QwtDate::Week0Type week0Type) Sets how to identify the first week of a year. **Parameters:** *week0Type* Mode 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()** ### int QwtDateScaleEngine::utcOffset () const **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()** ### QwtDate::Week0Type QwtDateScaleEngine::week0Type () const **Returns:** Setting how to identify the first week of a year. **See also:** **setWeek0Type()**, **maxWeeks()** ## Author Generated automatically by Doxygen for Qwt User's Guide from the source code.