Qwt User's Guide
QwtPlotHistogram Class Reference

QwtPlotHistogram represents a series of samples, where an interval is associated with a value ( $y = f([x1,x2])$ ). More...

#include <qwt_plot_histogram.h>

Inheritance diagram for QwtPlotHistogram:

Public Types

enum  HistogramStyle { Outline, Columns, Lines, UserStyle = 100 }

Public Member Functions

 QwtPlotHistogram (const QString &title=QString::null)
 QwtPlotHistogram (const QwtText &title)
virtual ~QwtPlotHistogram ()
 Destructor.
virtual int rtti () const
void setPen (const QColor &, qreal width=0.0, Qt::PenStyle=Qt::SolidLine)
void setPen (const QPen &)
const QPen & pen () const
void setBrush (const QBrush &)
const QBrush & brush () const
void setSamples (const QVector< QwtIntervalSample > &)
void setSamples (QwtSeriesData< QwtIntervalSample > *)
void setBaseline (double reference)
 Set the value of the baseline.
double baseline () const
void setStyle (HistogramStyle style)
HistogramStyle style () const
void setSymbol (const QwtColumnSymbol *)
 Assign a symbol.
const QwtColumnSymbolsymbol () const
virtual void drawSeries (QPainter *p, const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &canvasRect, int from, int to) const
virtual QRectF boundingRect () const
virtual QwtGraphic legendIcon (int index, const QSizeF &) const

Protected Member Functions

virtual QwtColumnRect columnRect (const QwtIntervalSample &, const QwtScaleMap &, const QwtScaleMap &) const
virtual void drawColumn (QPainter *, const QwtColumnRect &, const QwtIntervalSample &) const
void drawColumns (QPainter *, const QwtScaleMap &xMap, const QwtScaleMap &yMap, int from, int to) const
void drawOutline (QPainter *, const QwtScaleMap &xMap, const QwtScaleMap &yMap, int from, int to) const
void drawLines (QPainter *, const QwtScaleMap &xMap, const QwtScaleMap &yMap, int from, int to) const

Detailed Description

QwtPlotHistogram represents a series of samples, where an interval is associated with a value ( $y = f([x1,x2])$ ).

The representation depends on the style() and an optional symbol() that is displayed for each interval.

Note:
The term "histogram" is used in a different way in the areas of digital image processing and statistics. Wikipedia introduces the terms "image histogram" and "color histogram" to avoid confusions. While "image histograms" can be displayed by a QwtPlotCurve there is no applicable plot item for a "color histogram" yet.
See also:
QwtPlotBarChart, QwtPlotMultiBarChart

Member Enumeration Documentation

Histogram styles. The default style is QwtPlotHistogram::Columns.

See also:
setStyle(), style(), setSymbol(), symbol(), setBaseline()
Enumerator:
Outline 

Draw an outline around the area, that is build by all intervals using the pen() and fill it with the brush(). The outline style requires, that the intervals are in increasing order and not overlapping.

Columns 

Draw a column for each interval. When a symbol() has been set the symbol is used otherwise the column is displayed as plain rectangle using pen() and brush().

Lines 

Draw a simple line using the pen() for each interval.

UserStyle 

Styles >= UserStyle are reserved for derived classes that overload drawSeries() with additional application specific ways to display a histogram.


Constructor & Destructor Documentation

QwtPlotHistogram::QwtPlotHistogram ( const QString &  title = QString::null) [explicit]

Constructor

Parameters:
titleTitle of the histogram.
QwtPlotHistogram::QwtPlotHistogram ( const QwtText title) [explicit]

Constructor

Parameters:
titleTitle of the histogram.

Member Function Documentation

double QwtPlotHistogram::baseline ( ) const
Returns:
Value of the baseline
See also:
setBaseline()
QRectF QwtPlotHistogram::boundingRect ( ) const [virtual]
Returns:
Bounding rectangle of all samples. For an empty series the rectangle is invalid.

Reimplemented from QwtPlotSeriesItem.

const QBrush & QwtPlotHistogram::brush ( ) const
Returns:
Brush used in a style() depending way.
See also:
setPen(), brush()
QwtColumnRect QwtPlotHistogram::columnRect ( const QwtIntervalSample sample,
const QwtScaleMap xMap,
const QwtScaleMap yMap 
) const [protected, virtual]

Calculate the area that is covered by a sample

Parameters:
sampleSample
xMapMaps x-values into pixel coordinates.
yMapMaps y-values into pixel coordinates.
Returns:
Rectangle, that is covered by a sample
void QwtPlotHistogram::drawColumn ( QPainter *  painter,
const QwtColumnRect rect,
const QwtIntervalSample sample 
) const [protected, virtual]

Draw a column for a sample in Columns style().

When a symbol() has been set the symbol is used otherwise the column is displayed as plain rectangle using pen() and brush().

Parameters:
painterPainter
rectRectangle where to paint the column in paint device coordinates
sampleSample to be displayed
Note:
In applications, where different intervals need to be displayed in a different way ( f.e different colors or even using different symbols) it is recommended to overload drawColumn().
void QwtPlotHistogram::drawColumns ( QPainter *  painter,
const QwtScaleMap xMap,
const QwtScaleMap yMap,
int  from,
int  to 
) const [protected]

Draw a histogram in Columns style()

Parameters:
painterPainter
xMapMaps x-values into pixel coordinates.
yMapMaps y-values into pixel coordinates.
fromIndex of the first sample to be painted
toIndex of the last sample to be painted. If to < 0 the histogram will be painted to its last point.
See also:
setStyle(), style(), setSymbol(), drawColumn()
void QwtPlotHistogram::drawLines ( QPainter *  painter,
const QwtScaleMap xMap,
const QwtScaleMap yMap,
int  from,
int  to 
) const [protected]

Draw a histogram in Lines style()

Parameters:
painterPainter
xMapMaps x-values into pixel coordinates.
yMapMaps y-values into pixel coordinates.
fromIndex of the first sample to be painted
toIndex of the last sample to be painted. If to < 0 the histogram will be painted to its last point.
See also:
setStyle(), style(), setPen()
void QwtPlotHistogram::drawOutline ( QPainter *  painter,
const QwtScaleMap xMap,
const QwtScaleMap yMap,
int  from,
int  to 
) const [protected]

Draw a histogram in Outline style()

Parameters:
painterPainter
xMapMaps x-values into pixel coordinates.
yMapMaps y-values into pixel coordinates.
fromIndex of the first sample to be painted
toIndex of the last sample to be painted. If to < 0 the histogram will be painted to its last point.
See also:
setStyle(), style()
Warning:
The outline style requires, that the intervals are in increasing order and not overlapping.
void QwtPlotHistogram::drawSeries ( QPainter *  painter,
const QwtScaleMap xMap,
const QwtScaleMap yMap,
const QRectF &  canvasRect,
int  from,
int  to 
) const [virtual]

Draw a subset of the histogram samples

Parameters:
painterPainter
xMapMaps x-values into pixel coordinates.
yMapMaps y-values into pixel coordinates.
canvasRectContents rectangle of the canvas
fromIndex of the first sample to be painted
toIndex of the last sample to be painted. If to < 0 the series will be painted to its last sample.
See also:
drawOutline(), drawLines(), drawColumns

Implements QwtPlotSeriesItem.

QwtGraphic QwtPlotHistogram::legendIcon ( int  index,
const QSizeF &  size 
) const [virtual]

A plain rectangle without pen using the brush()

Parameters:
indexIndex of the legend entry ( ignored as there is only one )
sizeIcon size
Returns:
A graphic displaying the icon
See also:
QwtPlotItem::setLegendIconSize(), QwtPlotItem::legendData()

Reimplemented from QwtPlotItem.

const QPen & QwtPlotHistogram::pen ( ) const
Returns:
Pen used in a style() depending way.
See also:
setPen(), brush()
int QwtPlotHistogram::rtti ( ) const [virtual]
Returns:
QwtPlotItem::Rtti_PlotHistogram

Reimplemented from QwtPlotItem.

void QwtPlotHistogram::setBaseline ( double  value)

Set the value of the baseline.

Each column representing an QwtIntervalSample is defined by its interval and the interval between baseline and the value of the sample.

The default value of the baseline is 0.0.

Parameters:
valueValue of the baseline
See also:
baseline()
void QwtPlotHistogram::setBrush ( const QBrush &  brush)

Assign a brush, that is used in a style() depending way.

Parameters:
brushNew brush
See also:
pen(), brush()
void QwtPlotHistogram::setPen ( const QColor &  color,
qreal  width = 0.0,
Qt::PenStyle  style = Qt::SolidLine 
)

Build and assign a pen

In Qt5 the default pen width is 1.0 ( 0.0 in Qt4 ) what makes it non cosmetic ( see QPen::isCosmetic() ). This method has been introduced to hide this incompatibility.

Parameters:
colorPen color
widthPen width
stylePen style
See also:
pen(), brush()
void QwtPlotHistogram::setPen ( const QPen &  pen)

Assign a pen, that is used in a style() depending way.

Parameters:
penNew pen
See also:
pen(), brush()
void QwtPlotHistogram::setSamples ( const QVector< QwtIntervalSample > &  samples)

Initialize data with an array of samples.

Parameters:
samplesVector of points

Assign a series of samples

setSamples() is just a wrapper for setData() without any additional value - beside that it is easier to find for the developer.

Parameters:
dataData
Warning:
The item takes ownership of the data object, deleting it when its not used anymore.

Set the histogram's drawing style

Parameters:
styleHistogram style
See also:
HistogramStyle, style()
void QwtPlotHistogram::setSymbol ( const QwtColumnSymbol symbol)

Assign a symbol.

In Column style an optional symbol can be assigned, that is responsible for displaying the rectangle that is defined by the interval and the distance between baseline() and value. When no symbol has been defined the area is displayed as plain rectangle using pen() and brush().

See also:
style(), symbol(), drawColumn(), pen(), brush()
Note:
In applications, where different intervals need to be displayed in a different way ( f.e different colors or even using different symbols) it is recommended to overload drawColumn().
Returns:
Style of the histogram
See also:
HistogramStyle, setStyle()
Returns:
Current symbol or NULL, when no symbol has been assigned
See also:
setSymbol()

List of all members.

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