A helper class for translating a series of points. More...

#include <qwt_point_mapper.h>

Classes
class	PrivateData

Public Types
enum	TransformationFlag { RoundPoints = 0x01 , WeedOutPoints = 0x02 , WeedOutIntermediatePoints = 0x04 , PixelColumnReduce = 0x08 , LTTBReduce = 0x20 , MinMaxReduce = 0x10 , AdaptiveColumnReduce = 0x40 }
	Flags affecting the transformation process. More...

Public Member Functions
	QwtPointMapper ()
	Constructor.

void	setFlags (TransformationFlags)
	Set the flags affecting the transformation process.

TransformationFlags	flags () const
	Get the flags affecting the transformation process.

void	setFlag (TransformationFlag, bool on=true)
	Modify a flag affecting the transformation process.

bool	testFlag (TransformationFlag) const
	Test if a flag is set.

void	setBoundingRect (const QRectF &)
	Set a bounding rectangle for the point mapping algorithm.

QRectF	boundingRect () const
	Get the bounding rectangle.

void	setDevicePixelRatio (qreal ratio)
	Set the device pixel ratio of the target paint device.

qreal	devicePixelRatio () const
	Get the device pixel ratio of the target paint device.

QPolygonF	toPolygonF (const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QwtSeriesData< QPointF > *series, int from, int to) const
	Translate a series of points into a QPolygonF.

QPolygon	toPolygon (const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QwtSeriesData< QPointF > *series, int from, int to) const
	Translate a series of points into a QPolygon.

QPolygon	toPoints (const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QwtSeriesData< QPointF > *series, int from, int to) const
	Translate a series of points into a QPolygon (scattered points)

QPolygonF	toPointsF (const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QwtSeriesData< QPointF > *series, int from, int to) const
	Translate a series into a QPolygonF (scattered points)

QImage	toImage (const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QwtSeriesData< QPointF > *series, int from, int to, const QPen &, bool antialiased, uint numThreads) const
	Translate a series into a QImage.

Detailed Description

A helper class for translating a series of points.

QwtPointMapper is a collection of methods and optimizations for translating a series of points into paint device coordinates. It is used by QwtPlotCurve but might also be useful for similar plot items displaying a QwtSeriesData<QPointF>.

Member Enumeration Documentation

◆ TransformationFlag

enum QwtPointMapper::TransformationFlag

Flags affecting the transformation process.

See also: setFlag(), setFlags()

Enumerator
RoundPoints	Round points to the device pixel grid ( see devicePixelRatio() )
WeedOutPoints	Try to remove points, that are translated to the same position.
WeedOutIntermediatePoints	An even more aggressive weeding algorithm. An even more aggressive weeding algorithm, that can be used in toPolygon(). A consecutive chunk of points being mapped to the same x coordinate is reduced to 4 points: first point point with the minimum y coordinate point with the maximum y coordinate last point In the worst case (first and last points are never one of the extremes) the number of points will be 4 times the width. As the algorithm is fast it can be used inside of a polyline render cycle.
PixelColumnReduce	Pixel-column based downsampling. Allocates a bin array indexed by device pixel column ( see devicePixelRatio() ) and stores first/min/max/last Y per column. Output is at most 4 points per column. Requires a valid boundingRect() to determine the canvas width. Overrides WeedOutIntermediatePoints when both are set.
LTTBReduce	Largest-Triangle-Three-Buckets (LTTB) downsampling. Divides the visible data into equal-count buckets and keeps the sample of each bucket, that forms the largest triangle with the previously selected point and the average of the next bucket. The first and last sample are always kept. Target bucket count is 4 * boundingRect() width in device pixels ( see devicePixelRatio() ), the output is at most one point per bucket. Overrides WeedOutIntermediatePoints when both are set.
MinMaxReduce	MinMax bucket downsampling. Divides the visible data into equal-count buckets and keeps the min-Y and max-Y point from each bucket. Target bucket count is derived from boundingRect() width in device pixels ( see devicePixelRatio() ). Overrides WeedOutIntermediatePoints when both are set.
AdaptiveColumnReduce	Adaptive column reduce downsampling. Single pass O(n) reduction combining a density gate with an ordered vertical tolerance selection, all pixel quantities in device pixels ( see devicePixelRatio() ): When the visible samples are not denser than 2 points per device pixel column the data is mapped 1:1 without any reduction, so zooming in always restores full fidelity. Otherwise the samples are clustered by device pixel column. Inside a cluster the first sample, every sample whose mapped y differs by at least 1 device pixel from the last kept sample and the last sample are kept - in their original order and at their real sub pixel coordinates. In contrast to the min/max envelope per column ( PixelColumnReduce ) ramps stay ramps instead of degenerating into a 1px staircase of vertical strokes and horizontal steps. When this selection of a cluster would emit more than K = 4 + ( cluster y span in device pixels ) points ( high frequency noise inside one column ) the cluster falls back to an ordered first/min/max/last quadruple, so the output per column is bounded by K + 1 points. The deviation from the original curve is bounded by 1 device pixel vertically and one column horizontally, visible features of at least 1 device pixel ( including in-column extrema and spikes ) are kept in sample order. For smooth data the output size is roughly the vertical pixel travel. Overrides all other reduction flags when set.

Constructor & Destructor Documentation

◆ QwtPointMapper()

QwtPointMapper::QwtPointMapper ( )

Constructor.

Creates a QwtPointMapper with default settings.

Destructor

Destroys the QwtPointMapper and frees all allocated resources.

Member Function Documentation

◆ boundingRect()

QRectF QwtPointMapper::boundingRect ( ) const

Get the bounding rectangle.

Returns: Bounding rectangle

See also: setBoundingRect()

◆ devicePixelRatio()

qreal QwtPointMapper::devicePixelRatio ( ) const

Get the device pixel ratio of the target paint device.

Returns: Device pixel ratio

See also: setDevicePixelRatio()

◆ flags()

QwtPointMapper::TransformationFlags QwtPointMapper::flags ( ) const

Get the flags affecting the transformation process.

Returns: Flags affecting the transformation process

See also: setFlags(), setFlag()

◆ setBoundingRect()

void QwtPointMapper::setBoundingRect ( const QRectF & rect )

Set a bounding rectangle for the point mapping algorithm.

A valid bounding rectangle can be used for optimizations.

Parameters

[in] rect Bounding rectangle

See also: boundingRect()

◆ setDevicePixelRatio()

void QwtPointMapper::setDevicePixelRatio ( qreal ratio )

Set the device pixel ratio of the target paint device.

All pixel based reductions ( bucket counts, pixel columns ) and the rounding of RoundPoints are calculated in device pixels of the target paint device. On high DPI screens ( ratio > 1 ) this keeps the resolution of the reduction and the granularity of the rounding aligned with what the device can actually display. The mapped coordinates themselves remain in paint coordinates.

Parameters

[in] ratio Device pixel ratio - values <= 0 are reset to 1.0

See also: devicePixelRatio(), QwtPainter::devicePixelRatio()

◆ setFlag()

void QwtPointMapper::setFlag	(	TransformationFlag	flag,
		bool	on = `true`
	)

Modify a flag affecting the transformation process.

Parameters

[in]	flag	Flag type
[in]	on	Value

See also: testFlag(), setFlags()

◆ setFlags()

void QwtPointMapper::setFlags ( TransformationFlags flags )

Set the flags affecting the transformation process.

Parameters

[in] flags Flags

See also: flags(), setFlag()

◆ testFlag()

bool QwtPointMapper::testFlag ( TransformationFlag flag ) const

Test if a flag is set.

Parameters

[in] flag Flag type

Returns: True when the flag is set

See also: setFlag(), setFlags()

◆ toImage()

QImage QwtPointMapper::toImage	(	const QwtScaleMap &	xMap,
		const QwtScaleMap &	yMap,
		const QwtSeriesData< QPointF > *	series,
		int	from,
		int	to,
		const QPen &	pen,
		bool	antialiased,
		uint	numThreads
	)		const

Translate a series into a QImage.

Parameters

[in]	xMap	x map
[in]	yMap	y map
[in]	series	Series of points to be mapped
[in]	from	Index of the first point to be painted
[in]	to	Index of the last point to be painted
[in]	pen	Pen used for drawing a point of the image, where a point is mapped to
[in]	antialiased	True when the dots should be displayed antialiased
[in]	numThreads	Number of threads to be used for rendering. If numThreads is set to 0, the system specific ideal thread count is used.

Returns: Image displaying the series

◆ toPoints()

QPolygon QwtPointMapper::toPoints	(	const QwtScaleMap &	xMap,
		const QwtScaleMap &	yMap,
		const QwtSeriesData< QPointF > *	series,
		int	from,
		int	to
	)		const

Translate a series of points into a QPolygon (scattered points)

WeedOutPoints & boundingRect().isValid(): All points that are mapped to the same position will be one point. Points outside of the bounding rectangle are ignored.
WeedOutPoints & !boundingRect().isValid(): All consecutive points that are mapped to the same position will one point.
!WeedOutPoints & boundingRect().isValid(): Points outside of the bounding rectangle are ignored.

Parameters

[in]	xMap	x map
[in]	yMap	y map
[in]	series	Series of points to be mapped
[in]	from	Index of the first point to be painted
[in]	to	Index of the last point to be painted

Returns: Translated polygon

◆ toPointsF()

QPolygonF QwtPointMapper::toPointsF	(	const QwtScaleMap &	xMap,
		const QwtScaleMap &	yMap,
		const QwtSeriesData< QPointF > *	series,
		int	from,
		int	to
	)		const

Translate a series into a QPolygonF (scattered points)

WeedOutPoints & RoundPoints & boundingRect().isValid(): All points that are mapped to the same position will be one point. Points outside of the bounding rectangle are ignored.
WeedOutPoints & RoundPoints & !boundingRect().isValid(): All consecutive points that are mapped to the same position will one point.
WeedOutPoints & !RoundPoints: All consecutive points that are mapped to the same position will one point.
!WeedOutPoints & boundingRect().isValid(): Points outside of the bounding rectangle are ignored.

When RoundPoints is set, all points are rounded to the device pixel grid ( see devicePixelRatio() ) but returned as PolygonF - what only makes sense when the further processing of the values need a QPolygonF.

Parameters

[in]	xMap	x map
[in]	yMap	y map
[in]	series	Series of points to be mapped
[in]	from	Index of the first point to be painted
[in]	to	Index of the last point to be painted

Returns: Translated polygon

◆ toPolygon()

QPolygon QwtPointMapper::toPolygon	(	const QwtScaleMap &	xMap,
		const QwtScaleMap &	yMap,
		const QwtSeriesData< QPointF > *	series,
		int	from,
		int	to
	)		const

Translate a series of points into a QPolygon.

When the WeedOutPoints flag is enabled, consecutive points that are mapped to the same position will be one point.

Parameters

[in]	xMap	x map
[in]	yMap	y map
[in]	series	Series of points to be mapped
[in]	from	Index of the first point to be painted
[in]	to	Index of the last point to be painted

Returns: Translated polygon

◆ toPolygonF()

QPolygonF QwtPointMapper::toPolygonF	(	const QwtScaleMap &	xMap,
		const QwtScaleMap &	yMap,
		const QwtSeriesData< QPointF > *	series,
		int	from,
		int	to
	)		const

Translate a series of points into a QPolygonF.

When the WeedOutPoints flag is enabled, consecutive points that are mapped to the same position will be one point. When RoundPoints is set, all points are rounded to the device pixel grid ( see devicePixelRatio() ) but returned as PolygonF - what only makes sense when the further processing of the values need a QPolygonF. When WeedOutIntermediatePoints is enabled, an even more aggressive weeding algorithm is enabled. It rounds to device pixels on its own and does not require RoundPoints to be set.

Parameters

[in]	xMap	x map
[in]	yMap	y map
[in]	series	Series of points to be mapped
[in]	from	Index of the first point to be painted
[in]	to	Index of the last point to be painted

Returns: Translated polygon

The documentation for this class was generated from the following files:

/home/runner/work/QWT/QWT/src/plot/qwt_point_mapper.h
/home/runner/work/QWT/QWT/src/plot/qwt_point_mapper.cpp

Classes

Public Types

Public Member Functions

Detailed Description

Member Enumeration Documentation

◆ TransformationFlag

Constructor & Destructor Documentation

◆ QwtPointMapper()

Member Function Documentation

◆ boundingRect()

◆ devicePixelRatio()

◆ flags()

◆ setBoundingRect()

◆ setDevicePixelRatio()

◆ setFlag()

◆ setFlags()

◆ testFlag()

◆ toImage()

◆ toPoints()

◆ toPointsF()

◆ toPolygon()

◆ toPolygonF()