Qwt User's Guide
QwtPlotItem Class Reference

Base class for items on the plot canvas. More...

#include <qwt_plot_item.h>

Inheritance diagram for QwtPlotItem:

Public Types

enum  RttiValues {
  Rtti_PlotItem = 0, Rtti_PlotGrid, Rtti_PlotScale, Rtti_PlotLegend,
  Rtti_PlotMarker, Rtti_PlotCurve, Rtti_PlotSpectroCurve, Rtti_PlotIntervalCurve,
  Rtti_PlotHistogram, Rtti_PlotSpectrogram, Rtti_PlotSVG, Rtti_PlotTradingCurve,
  Rtti_PlotBarChart, Rtti_PlotMultiBarChart, Rtti_PlotShape, Rtti_PlotTextLabel,
  Rtti_PlotZone, Rtti_PlotUserItem = 1000
}
 Runtime type information. More...
enum  ItemAttribute { Legend = 0x01, AutoScale = 0x02, Margins = 0x04 }
 Plot Item Attributes. More...
enum  ItemInterest { ScaleInterest = 0x01, LegendInterest = 0x02 }
 Plot Item Interests. More...
enum  RenderHint { RenderAntialiased = 0x1 }
 Render hints. More...
typedef QFlags< ItemAttributeItemAttributes
 Plot Item Attributes.
typedef QFlags< ItemInterestItemInterests
 Plot Item Interests.
typedef QFlags< RenderHintRenderHints
 Render hints.

Public Member Functions

 QwtPlotItem (const QwtText &title=QwtText())
virtual ~QwtPlotItem ()
 Destroy the QwtPlotItem.
void attach (QwtPlot *plot)
 Attach the item to a plot.
void detach ()
 This method detaches a QwtPlotItem from any QwtPlot it has been associated with.
QwtPlotplot () const
 Return attached plot.
void setTitle (const QString &title)
void setTitle (const QwtText &title)
const QwtTexttitle () const
virtual int rtti () const
void setItemAttribute (ItemAttribute, bool on=true)
bool testItemAttribute (ItemAttribute) const
void setItemInterest (ItemInterest, bool on=true)
bool testItemInterest (ItemInterest) const
void setRenderHint (RenderHint, bool on=true)
bool testRenderHint (RenderHint) const
void setRenderThreadCount (uint numThreads)
uint renderThreadCount () const
void setLegendIconSize (const QSize &)
QSize legendIconSize () const
double z () const
void setZ (double z)
 Set the z value.
void show ()
 Show the item.
void hide ()
 Hide the item.
virtual void setVisible (bool)
bool isVisible () const
void setAxes (int xAxis, int yAxis)
void setXAxis (int axis)
int xAxis () const
 Return xAxis.
void setYAxis (int axis)
int yAxis () const
 Return yAxis.
virtual void itemChanged ()
virtual void legendChanged ()
virtual void draw (QPainter *painter, const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &canvasRect) const =0
 Draw the item.
virtual QRectF boundingRect () const
virtual void getCanvasMarginHint (const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &canvasSize, double &left, double &top, double &right, double &bottom) const
 Calculate a hint for the canvas margin.
virtual void updateScaleDiv (const QwtScaleDiv &, const QwtScaleDiv &)
 Update the item to changes of the axes scale division.
virtual void updateLegend (const QwtPlotItem *, const QList< QwtLegendData > &)
 Update the item to changes of the legend info.
QRectF scaleRect (const QwtScaleMap &, const QwtScaleMap &) const
 Calculate the bounding scale rectangle of 2 maps.
QRectF paintRect (const QwtScaleMap &, const QwtScaleMap &) const
 Calculate the bounding paint rectangle of 2 maps.
virtual QList< QwtLegendDatalegendData () const
 Return all information, that is needed to represent the item on the legend.
virtual QwtGraphic legendIcon (int index, const QSizeF &) const

Protected Member Functions

QwtGraphic defaultIcon (const QBrush &, const QSizeF &) const
 Return a default icon from a brush.

Detailed Description

Base class for items on the plot canvas.

A plot item is "something", that can be painted on the plot canvas, or only affects the scales of the plot widget. They can be categorized as:

  • Representator
    A "Representator" is an item that represents some sort of data on the plot canvas. The different representator classes are organized according to the characteristics of the data:

Depending on the QwtPlotItem::ItemAttribute flags, an item is included into autoscaling or has an entry on the legend.

Before misusing the existing item classes it might be better to implement a new type of plot item ( don't implement a watermark as spectrogram ). Deriving a new type of QwtPlotItem primarily means to implement the YourPlotItem::draw() method.

See also:
The cpuplot example shows the implementation of additional plot items.

Member Enumeration Documentation

Plot Item Attributes.

Various aspects of a plot widget depend on the attributes of the attached plot items. If and how a single plot item participates in these updates depends on its attributes.

See also:
setItemAttribute(), testItemAttribute(), ItemInterest
Enumerator:
Legend 

The item is represented on the legend.

AutoScale 

The boundingRect() of the item is included in the autoscaling calculation as long as its width or height is >= 0.0.

Margins 

The item needs extra space to display something outside its bounding rectangle.

See also:
getCanvasMarginHint()

Plot Item Interests.

Plot items might depend on the situation of the corresponding plot widget. By enabling an interest the plot item will be notified, when the corresponding attribute of the plot widgets has changed.

See also:
setItemAttribute(), testItemAttribute(), ItemInterest
Enumerator:
ScaleInterest 

The item is interested in updates of the scales

See also:
updateScaleDiv()
LegendInterest 

The item is interested in updates of the legend ( of other items ) This flag is intended for items, that want to implement a legend for displaying entries of other plot item.

Note:
If the plot item wants to be represented on a legend enable QwtPlotItem::Legend instead.
See also:
updateLegend()

Render hints.

Enumerator:
RenderAntialiased 

Enable antialiasing.

Runtime type information.

RttiValues is used to cast plot items, without having to enable runtime type information of the compiler.

Enumerator:
Rtti_PlotItem 

Unspecific value, that can be used, when it doesn't matter.

Rtti_PlotGrid 

For QwtPlotGrid.

Rtti_PlotScale 

For QwtPlotScaleItem.

Rtti_PlotLegend 

For QwtPlotLegendItem.

Rtti_PlotMarker 

For QwtPlotMarker.

Rtti_PlotCurve 

For QwtPlotCurve.

Rtti_PlotSpectroCurve 

For QwtPlotSpectroCurve.

Rtti_PlotIntervalCurve 

For QwtPlotIntervalCurve.

Rtti_PlotHistogram 

For QwtPlotHistogram.

Rtti_PlotSpectrogram 

For QwtPlotSpectrogram.

Rtti_PlotSVG 

For QwtPlotSvgItem.

Rtti_PlotTradingCurve 

For QwtPlotTradingCurve.

Rtti_PlotBarChart 

For QwtPlotBarChart.

Rtti_PlotMultiBarChart 

For QwtPlotMultiBarChart.

Rtti_PlotShape 

For QwtPlotShapeItem.

Rtti_PlotTextLabel 

For QwtPlotTextLabel.

Rtti_PlotZone 

For QwtPlotZoneItem.

Rtti_PlotUserItem 

Values >= Rtti_PlotUserItem are reserved for plot items not implemented in the Qwt library.


Constructor & Destructor Documentation

QwtPlotItem::QwtPlotItem ( const QwtText title = QwtText()) [explicit]

Constructor

Parameters:
titleTitle of the item

Member Function Documentation

void QwtPlotItem::attach ( QwtPlot plot)

Attach the item to a plot.

This method will attach a QwtPlotItem to the QwtPlot argument. It will first detach the QwtPlotItem from any plot from a previous call to attach (if necessary). If a NULL argument is passed, it will detach from any QwtPlot it was attached to.

Parameters:
plotPlot widget
See also:
detach()
QRectF QwtPlotItem::boundingRect ( ) const [virtual]
Returns:
An invalid bounding rect: QRectF(1.0, 1.0, -2.0, -2.0)
Note:
A width or height < 0.0 is ignored by the autoscaler

Reimplemented in QwtPlotTradingCurve, QwtPlotMarker, QwtPlotIntervalCurve, QwtPlotHistogram, QwtPlotRasterItem, QwtPlotShapeItem, QwtPlotBarChart, QwtPlotMultiBarChart, QwtPlotZoneItem, QwtPlotSeriesItem, and QwtPlotSvgItem.

QwtGraphic QwtPlotItem::defaultIcon ( const QBrush &  brush,
const QSizeF &  size 
) const [protected]

Return a default icon from a brush.

The default icon is a filled rectangle used in several derived classes as legendIcon().

Parameters:
brushFill brush
sizeIcon size
Returns:
A filled rectangle

This method detaches a QwtPlotItem from any QwtPlot it has been associated with.

detach() is equivalent to calling attach( NULL )

See also:
attach()
virtual void QwtPlotItem::draw ( QPainter *  painter,
const QwtScaleMap xMap,
const QwtScaleMap yMap,
const QRectF &  canvasRect 
) const [pure virtual]

Draw the item.

Parameters:
painterPainter
xMapMaps x-values into pixel coordinates.
yMapMaps y-values into pixel coordinates.
canvasRectContents rect of the canvas in painter coordinates

Implemented in QwtPlotMarker, QwtPlotLegendItem, QwtPlotRasterItem, QwtPlotShapeItem, QwtPlotSpectrogram, QwtPlotScaleItem, QwtPlotGrid, QwtPlotTextLabel, QwtPlotZoneItem, QwtPlotSvgItem, and QwtPlotSeriesItem.

void QwtPlotItem::getCanvasMarginHint ( const QwtScaleMap xMap,
const QwtScaleMap yMap,
const QRectF &  canvasRect,
double &  left,
double &  top,
double &  right,
double &  bottom 
) const [virtual]

Calculate a hint for the canvas margin.

When the QwtPlotItem::Margins flag is enabled the plot item indicates, that it needs some margins at the borders of the canvas. This is f.e. used by bar charts to reserve space for displaying the bars.

The margins are in target device coordinates ( pixels on screen )

Parameters:
xMapMaps x-values into pixel coordinates.
yMapMaps y-values into pixel coordinates.
canvasRectContents rectangle of the canvas in painter coordinates
leftReturns the left margin
topReturns the top margin
rightReturns the right margin
bottomReturns the bottom margin
Returns:
The default implementation returns 0 for all margins
See also:
QwtPlot::getCanvasMarginsHint(), QwtPlot::updateCanvasMargins()

Reimplemented in QwtPlotAbstractBarChart.

bool QwtPlotItem::isVisible ( ) const
Returns:
true if visible
See also:
setVisible(), show(), hide()
void QwtPlotItem::itemChanged ( ) [virtual]

Update the legend and call QwtPlot::autoRefresh() for the parent plot.

See also:
QwtPlot::legendChanged(), QwtPlot::autoRefresh()
void QwtPlotItem::legendChanged ( ) [virtual]

Update the legend of the parent plot.

See also:
QwtPlot::updateLegend(), itemChanged()
QList< QwtLegendData > QwtPlotItem::legendData ( ) const [virtual]

Return all information, that is needed to represent the item on the legend.

Most items are represented by one entry on the legend showing an icon and a text, but f.e. QwtPlotMultiBarChart displays one entry for each bar.

QwtLegendData is basically a list of QVariants that makes it possible to overload and reimplement legendData() to return almost any type of information, that is understood by the receiver that acts as the legend.

The default implementation returns one entry with the title() of the item and the legendIcon().

Returns:
Data, that is needed to represent the item on the legend
See also:
title(), legendIcon(), QwtLegend, QwtPlotLegendItem

Reimplemented in QwtPlotBarChart, and QwtPlotMultiBarChart.

QwtGraphic QwtPlotItem::legendIcon ( int  index,
const QSizeF &  size 
) const [virtual]
Returns:
Icon representing the item on the legend

The default implementation returns an invalid icon

Parameters:
indexIndex of the legend entry ( usually there is only one )
sizeIcon size
See also:
setLegendIconSize(), legendData()

Reimplemented in QwtPlotCurve, QwtPlotTradingCurve, QwtPlotMarker, QwtPlotIntervalCurve, QwtPlotHistogram, QwtPlotBarChart, QwtPlotShapeItem, and QwtPlotMultiBarChart.

QSize QwtPlotItem::legendIconSize ( ) const
Returns:
Legend icon size
See also:
setLegendIconSize(), legendIcon()
QRectF QwtPlotItem::paintRect ( const QwtScaleMap xMap,
const QwtScaleMap yMap 
) const

Calculate the bounding paint rectangle of 2 maps.

Parameters:
xMapMaps x-values into pixel coordinates.
yMapMaps y-values into pixel coordinates.
Returns:
Bounding paint rectangle of the scale maps, not normalized
Returns:
Number of threads to be used for rendering. If numThreads() is set to 0, the system specific ideal thread count is used.
int QwtPlotItem::rtti ( ) const [virtual]

Return rtti for the specific class represented. QwtPlotItem is simply a virtual interface class, and base classes will implement this method with specific rtti values so a user can differentiate them.

The rtti value is useful for environments, where the runtime type information is disabled and it is not possible to do a dynamic_cast<...>.

Returns:
rtti value
See also:
RttiValues

Reimplemented in QwtPlotCurve, QwtPlotTradingCurve, QwtPlotShapeItem, QwtPlotSpectrogram, QwtPlotIntervalCurve, QwtPlotHistogram, QwtPlotMarker, QwtPlotBarChart, QwtPlotMultiBarChart, QwtPlotLegendItem, QwtPlotScaleItem, QwtPlotTextLabel, QwtPlotSpectroCurve, QwtPlotSvgItem, QwtPlotGrid, and QwtPlotZoneItem.

QRectF QwtPlotItem::scaleRect ( const QwtScaleMap xMap,
const QwtScaleMap yMap 
) const

Calculate the bounding scale rectangle of 2 maps.

Parameters:
xMapMaps x-values into pixel coordinates.
yMapMaps y-values into pixel coordinates.
Returns:
Bounding scale rect of the scale maps, not normalized
void QwtPlotItem::setAxes ( int  xAxis,
int  yAxis 
)

Set X and Y axis

The item will painted according to the coordinates of its Axes.

Parameters:
xAxisX Axis ( QwtPlot::xBottom or QwtPlot::xTop )
yAxisY Axis ( QwtPlot::yLeft or QwtPlot::yRight )
See also:
setXAxis(), setYAxis(), xAxis(), yAxis(), QwtPlot::Axis
void QwtPlotItem::setItemAttribute ( ItemAttribute  attribute,
bool  on = true 
)

Toggle an item attribute

Parameters:
attributeAttribute type
ontrue/false
See also:
testItemAttribute(), ItemInterest
void QwtPlotItem::setItemInterest ( ItemInterest  interest,
bool  on = true 
)

Toggle an item interest

Parameters:
interestInterest type
ontrue/false
See also:
testItemInterest(), ItemAttribute
void QwtPlotItem::setLegendIconSize ( const QSize &  size)

Set the size of the legend icon

The default setting is 8x8 pixels

Parameters:
sizeSize
See also:
legendIconSize(), legendIcon()
void QwtPlotItem::setRenderHint ( RenderHint  hint,
bool  on = true 
)

Toggle an render hint

Parameters:
hintRender hint
ontrue/false
See also:
testRenderHint(), RenderHint
void QwtPlotItem::setRenderThreadCount ( uint  numThreads)

On multi core systems rendering of certain plot item ( f.e QwtPlotRasterItem ) can be done in parallel in several threads.

The default setting is set to 1.

Parameters:
numThreadsNumber of threads to be used for rendering. If numThreads is set to 0, the system specific ideal thread count is used.

The default thread count is 1 ( = no additional threads )

void QwtPlotItem::setTitle ( const QString &  title)

Set a new title

Parameters:
titleTitle
See also:
title()
void QwtPlotItem::setTitle ( const QwtText title)

Set a new title

Parameters:
titleTitle
See also:
title()
void QwtPlotItem::setVisible ( bool  on) [virtual]

Show/Hide the item

Parameters:
onShow if true, otherwise hide
See also:
isVisible(), show(), hide()
void QwtPlotItem::setXAxis ( int  axis)

Set the X axis

The item will painted according to the coordinates its Axes.

Parameters:
axisX Axis ( QwtPlot::xBottom or QwtPlot::xTop )
See also:
setAxes(), setYAxis(), xAxis(), QwtPlot::Axis
void QwtPlotItem::setYAxis ( int  axis)

Set the Y axis

The item will painted according to the coordinates its Axes.

Parameters:
axisY Axis ( QwtPlot::yLeft or QwtPlot::yRight )
See also:
setAxes(), setXAxis(), yAxis(), QwtPlot::Axis
void QwtPlotItem::setZ ( double  z)

Set the z value.

Plot items are painted in increasing z-order.

Parameters:
zZ-value
See also:
z(), QwtPlotDict::itemList()
bool QwtPlotItem::testItemAttribute ( ItemAttribute  attribute) const

Test an item attribute

Parameters:
attributeAttribute type
Returns:
true/false
See also:
setItemAttribute(), ItemInterest
bool QwtPlotItem::testItemInterest ( ItemInterest  interest) const

Test an item interest

Parameters:
interestInterest type
Returns:
true/false
See also:
setItemInterest(), ItemAttribute

Test a render hint

Parameters:
hintRender hint
Returns:
true/false
See also:
setRenderHint(), RenderHint
const QwtText & QwtPlotItem::title ( ) const
Returns:
Title of the item
See also:
setTitle()
void QwtPlotItem::updateLegend ( const QwtPlotItem item,
const QList< QwtLegendData > &  data 
) [virtual]

Update the item to changes of the legend info.

Plot items that want to display a legend ( not those, that want to be displayed on a legend ! ) will have to implement updateLegend().

updateLegend() is only called when the LegendInterest interest is enabled. The default implementation does nothing.

Parameters:
itemPlot item to be displayed on a legend
dataAttributes how to display item on the legend
See also:
QwtPlotLegendItem
Note:
Plot items, that want to be displayed on a legend need to enable the QwtPlotItem::Legend flag and to implement legendData() and legendIcon()

Reimplemented in QwtPlotLegendItem.

void QwtPlotItem::updateScaleDiv ( const QwtScaleDiv xScaleDiv,
const QwtScaleDiv yScaleDiv 
) [virtual]

Update the item to changes of the axes scale division.

Update the item, when the axes of plot have changed. The default implementation does nothing, but items that depend on the scale division (like QwtPlotGrid()) have to reimplement updateScaleDiv()

updateScaleDiv() is only called when the ScaleInterest interest is enabled. The default implementation does nothing.

Parameters:
xScaleDivScale division of the x-axis
yScaleDivScale division of the y-axis
See also:
QwtPlot::updateAxes(), ScaleInterest

Reimplemented in QwtPlotScaleItem, QwtPlotGrid, and QwtPlotSeriesItem.

double QwtPlotItem::z ( ) const

Plot items are painted in increasing z-order.

Returns:
setZ(), QwtPlotDict::itemList()

List of all members.

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