QwtPlot(3) Qwt User's Guide QwtPlot(3)

QwtPlot - A 2-D plotting widget.

#include <qwt_plot.h>

Inherits QFrame, and QwtPlotDict.


enum Axis { yLeft, yRight, xBottom, xTop, axisCnt }
Axis index. enum LegendPosition { LeftLegend, RightLegend, BottomLegend, TopLegend }


virtual void replot ()
Redraw the plot. void autoRefresh ()
Replots the plot if autoReplot() is true.


void itemAttached (QwtPlotItem *plotItem, bool on)
void legendDataChanged (const QVariant &itemInfo, const QList< QwtLegendData > &data)


QwtPlot (QWidget *=NULL)
Constructor. QwtPlot (const QwtText &title, QWidget *=NULL)
Constructor. virtual ~QwtPlot ()
Destructor. void applyProperties (const QString &)
QString grabProperties () const
void setAutoReplot (bool=true)
Set or reset the autoReplot option. bool autoReplot () const
void setPlotLayout (QwtPlotLayout *)
Assign a new plot layout. QwtPlotLayout * plotLayout ()
const QwtPlotLayout * plotLayout () const
void setTitle (const QString &)
void setTitle (const QwtText &)
QwtText title () const
QwtTextLabel * titleLabel ()
const QwtTextLabel * titleLabel () const
void setFooter (const QString &)
void setFooter (const QwtText &)
QwtText footer () const
QwtTextLabel * footerLabel ()
const QwtTextLabel * footerLabel () const
void setCanvas (QWidget *)
Set the drawing canvas of the plot widget. QWidget * canvas ()
const QWidget * canvas () const
void setCanvasBackground (const QBrush &)
Change the background of the plotting area. QBrush canvasBackground () const
virtual QwtScaleMap canvasMap (int axisId) const
double invTransform (int axisId, int pos) const
double transform (int axisId, double value) const
Transform a value into a coordinate in the plotting region. QwtScaleEngine * axisScaleEngine (int axisId)
const QwtScaleEngine * axisScaleEngine (int axisId) const
void setAxisScaleEngine (int axisId, QwtScaleEngine *)
void setAxisAutoScale (int axisId, bool on=true)
Enable autoscaling for a specified axis. bool axisAutoScale (int axisId) const
void enableAxis (int axisId, bool tf=true)
Enable or disable a specified axis. bool axisEnabled (int axisId) const
void setAxisFont (int axisId, const QFont &)
Change the font of an axis. QFont axisFont (int axisId) const
void setAxisScale (int axisId, double min, double max, double stepSize=0)
Disable autoscaling and specify a fixed scale for a selected axis. void setAxisScaleDiv (int axisId, const QwtScaleDiv &)
Disable autoscaling and specify a fixed scale for a selected axis. void setAxisScaleDraw (int axisId, QwtScaleDraw *)
Set a scale draw. double axisStepSize (int axisId) const
Return the step size parameter that has been set in setAxisScale. QwtInterval axisInterval (int axisId) const
Return the current interval of the specified axis. const QwtScaleDiv & axisScaleDiv (int axisId) const
Return the scale division of a specified axis. const QwtScaleDraw * axisScaleDraw (int axisId) const
Return the scale draw of a specified axis. QwtScaleDraw * axisScaleDraw (int axisId)
Return the scale draw of a specified axis. const QwtScaleWidget * axisWidget (int axisId) const
QwtScaleWidget * axisWidget (int axisId)
void setAxisLabelAlignment (int axisId, Qt::Alignment)
void setAxisLabelRotation (int axisId, double rotation)
void setAxisTitle (int axisId, const QString &)
Change the title of a specified axis. void setAxisTitle (int axisId, const QwtText &)
Change the title of a specified axis. QwtText axisTitle (int axisId) const
void setAxisMaxMinor (int axisId, int maxMinor)
int axisMaxMinor (int axisId) const
void setAxisMaxMajor (int axisId, int maxMajor)
int axisMaxMajor (int axisId) const
void insertLegend (QwtAbstractLegend *, LegendPosition=QwtPlot::RightLegend, double ratio=-1.0)
Insert a legend. QwtAbstractLegend * legend ()
const QwtAbstractLegend * legend () const
void updateLegend ()
void updateLegend (const QwtPlotItem *)
virtual QSize sizeHint () const
virtual QSize minimumSizeHint () const
Return a minimum size hint. virtual void updateLayout ()
Adjust plot content to its current size. virtual void drawCanvas (QPainter *)
void updateAxes ()
Rebuild the axes scales. void updateCanvasMargins ()
Update the canvas margins. virtual void getCanvasMarginsHint (const QwtScaleMap maps[], const QRectF &canvasRect, double &left, double &top, double &right, double &bottom) const
Calculate the canvas margins. virtual bool event (QEvent *)
Adds handling of layout requests. virtual bool eventFilter (QObject *, QEvent *)
Event filter. virtual void drawItems (QPainter *, const QRectF &, const QwtScaleMap maps[axisCnt]) const
virtual QVariant itemToInfo (QwtPlotItem *) const
Build an information, that can be used to identify a plot item on the legend. virtual QwtPlotItem * infoToItem (const QVariant &) const
Identify the plot item according to an item info object, that has bee generated from itemToInfo().


virtual void resizeEvent (QResizeEvent *e)


static bool axisValid (int axisId)

A 2-D plotting widget.

QwtPlot is a widget for plotting two-dimensional graphs. An unlimited number of plot items can be displayed on its canvas. Plot items might be curves (QwtPlotCurve), markers (QwtPlotMarker), the grid (QwtPlotGrid), or anything else derived from QwtPlotItem. A plot can have up to four axes, with each plot item attached to an x- and a y axis. The scales at the axes can be explicitly set (QwtScaleDiv), or are calculated from the plot items, using algorithms (QwtScaleEngine) which can be configured separately for each axis.

The simpleplot example is a good starting point to see how to set up a plot widget.

Example

The following example shows (schematically) the most simple way to use QwtPlot. By default, only the left and bottom axes are visible and their scales are computed automatically. 

#include <qwt_plot.h>
#include <qwt_plot_curve.h>
QwtPlot *myPlot = new QwtPlot( "Two Curves", parent );
// add curves
QwtPlotCurve *curve1 = new QwtPlotCurve( "Curve 1" );
QwtPlotCurve *curve2 = new QwtPlotCurve( "Curve 2" );
// connect or copy the data to the curves
curve1->setData( ... );
curve2->setData( ... );
curve1->attach( myPlot );
curve2->attach( myPlot );
// finally, refresh the plot
myPlot->replot();

enum QwtPlot::Axis

Axis index.

Enumerator

Y axis left of the canvas.
Y axis right of the canvas.
X axis below the canvas.
X axis above the canvas.
Number of axes.

enum QwtPlot::LegendPosition

Position of the legend, relative to the canvas.

See also:

insertLegend()

Enumerator

The legend will be left from the QwtPlot::yLeft axis.
The legend will be right from the QwtPlot::yRight axis.
The legend will be below the footer.
The legend will be above the title.

Constructor.

Parameters:

parent Parent widget

Constructor.

Parameters:

title Title text
parent Parent widget

This method is intended for manipulating the plot widget from a specific editor in the Qwt designer plugin.

Warning:

The plot editor has never been implemented.

Returns:

true if the autoReplot option is set.

See also:

setAutoReplot()

Returns:

True, if autoscaling is enabled

Parameters:

axisId Axis index

Returns:

True, if a specified axis is enabled

Parameters:

axisId Axis index

Returns:

The font of the scale labels for a specified axis

Parameters:

axisId Axis index

QwtInterval QwtPlot::axisInterval (int axisId) const

Return the current interval of the specified axis. This is only a convenience function for axisScaleDiv( axisId )->interval();

Parameters:

axisId Axis index

Returns:

Scale interval

See also:

QwtScaleDiv, axisScaleDiv()

Returns:

The maximum number of major ticks for a specified axis

Parameters:

axisId Axis index

See also:

setAxisMaxMajor(), QwtScaleEngine::divideScale()

Returns:

the maximum number of minor ticks for a specified axis

Parameters:

axisId Axis index

See also:

setAxisMaxMinor(), QwtScaleEngine::divideScale()

const QwtScaleDiv & QwtPlot::axisScaleDiv (int axisId) const

Return the scale division of a specified axis. axisScaleDiv(axisId).lowerBound(), axisScaleDiv(axisId).upperBound() are the current limits of the axis scale.

Parameters:

axisId Axis index

Returns:

Scale division

See also:

QwtScaleDiv, setAxisScaleDiv(), QwtScaleEngine::divideScale()

const QwtScaleDraw * QwtPlot::axisScaleDraw (int axisId) const

Return the scale draw of a specified axis.

Parameters:

axisId Axis index

Returns:

Specified scaleDraw for axis, or NULL if axis is invalid.

QwtScaleDraw * QwtPlot::axisScaleDraw (int axisId)

Return the scale draw of a specified axis.

Parameters:

axisId Axis index

Returns:

Specified scaleDraw for axis, or NULL if axis is invalid.

QwtScaleEngine * QwtPlot::axisScaleEngine (int axisId)

Parameters:

axisId Axis index

Returns:

Scale engine for a specific axis

const QwtScaleEngine * QwtPlot::axisScaleEngine (int axisId) const

Parameters:

axisId Axis index

Returns:

Scale engine for a specific axis

Return the step size parameter that has been set in setAxisScale. This doesn't need to be the step size of the current scale.

Parameters:

axisId Axis index

Returns:

step size parameter value

See also:

setAxisScale(), QwtScaleEngine::divideScale()

QwtText QwtPlot::axisTitle (int axisId) const

Returns:

Title of a specified axis

Parameters:

axisId Axis index

Returns:

true if the specified axis exists, otherwise false

Parameters:

axisId axis index

const QwtScaleWidget * QwtPlot::axisWidget (int axisId) const

Returns:

Scale widget of the specified axis, or NULL if axisId is invalid.

Parameters:

axisId Axis index

QwtScaleWidget * QwtPlot::axisWidget (int axisId)

Returns:

Scale widget of the specified axis, or NULL if axisId is invalid.

Parameters:

axisId Axis index

Returns:

the plot's canvas

Returns:

the plot's canvas

Nothing else than: canvas()->palette().brush( QPalette::Normal, QPalette::Window);

Returns:

Background brush of the plotting area.

See also:

setCanvasBackground()

QwtScaleMap QwtPlot::canvasMap (int axisId) const [virtual]

Parameters:

axisId Axis

Returns:

Map for the axis on the canvas. With this map pixel coordinates can translated to plot coordinates and vice versa.

See also:

QwtScaleMap, transform(), invTransform()

Redraw the canvas.

Parameters:

painter Painter used for drawing

Warning:

drawCanvas calls drawItems what is also used for printing. Applications that like to add individual plot items better overload drawItems()

See also:

drawItems()

Redraw the canvas items.

Parameters:

painter Painter used for drawing
canvasRect Bounding rectangle where to paint
maps QwtPlot::axisCnt maps, mapping between plot and paint device coordinates

Note:

Usually canvasRect is contentsRect() of the plot canvas. Due to a bug in Qt this rectangle might be wrong for certain frame styles ( f.e QFrame::Box ) and it might be necessary to fix the margins manually using QWidget::setContentsMargins()

Enable or disable a specified axis. When an axis is disabled, this only means that it is not visible on the screen. Curves, markers and can be attached to disabled axes, and transformation of screen coordinates into values works as normal.

Only xBottom and yLeft are enabled by default.

Parameters:

axisId Axis index
tf true (enabled) or false (disabled)

Adds handling of layout requests.

Parameters:

event Event

Returns:

See QFrame::event()

Event filter. The plot handles the following events for the canvas:

  • QEvent::Resize The canvas margins might depend on its size
  • QEvent::ContentsRectChange The layout needs to be recalculated

Parameters:

object Object to be filtered
event Event

Returns:

See QFrame::eventFilter()

See also:

updateCanvasMargins(), updateLayout()

QwtText QwtPlot::footer () const

Returns:

Text of the footer

QwtTextLabel * QwtPlot::footerLabel ()

Returns:

Footer label widget.

const QwtTextLabel * QwtPlot::footerLabel () const

Returns:

Footer label widget.

Calculate the canvas margins.

Parameters:

maps QwtPlot::axisCnt maps, mapping between plot and paint device coordinates
canvasRect Bounding rectangle where to paint
left Return parameter for the left margin
top Return parameter for the top margin
right Return parameter for the right margin
bottom Return parameter for the bottom margin

Plot items might indicate, that they need some extra space at the borders of the canvas by the QwtPlotItem::Margins flag.

updateCanvasMargins(), QwtPlotItem::getCanvasMarginHint()

This method is intended for manipulating the plot widget from a specific editor in the Qwt designer plugin.

Returns:

QString()

Warning:

The plot editor has never been implemented.

QwtPlotItem * QwtPlot::infoToItem (const QVariant & itemInfo) const [virtual]

Identify the plot item according to an item info object, that has bee generated from itemToInfo(). The default implementation simply tries to unwrap a QwtPlotItem pointer:

if ( itemInfo.canConvert<QwtPlotItem *>() )
    return qvariant_cast<QwtPlotItem *>( itemInfo );

Parameters:

itemInfo Plot item

Returns:

A plot item, when successful, otherwise a NULL pointer.

See also:

itemToInfo()

Insert a legend. If the position legend is QwtPlot::LeftLegend or QwtPlot::RightLegend the legend will be organized in one column from top to down. Otherwise the legend items will be placed in a table with a best fit number of columns from left to right.

insertLegend() will set the plot widget as parent for the legend. The legend will be deleted in the destructor of the plot or when another legend is inserted.

Legends, that are not inserted into the layout of the plot widget need to connect to the legendDataChanged() signal. Calling updateLegend() initiates this signal for an initial update. When the application code wants to implement its own layout this also needs to be done for rendering plots to a document ( see QwtPlotRenderer ).

Parameters:

legend Legend
pos The legend's position. For top/left position the number of columns will be limited to 1, otherwise it will be set to unlimited.
ratio Ratio between legend and the bounding rectangle of title, canvas and axes. The legend will be shrunk if it would need more space than the given ratio. The ratio is limited to ]0.0 .. 1.0]. In case of <= 0.0 it will be reset to the default ratio. The default vertical/horizontal ratio is 0.33/0.5.

See also:

legend(), QwtPlotLayout::legendPosition(), QwtPlotLayout::setLegendPosition()

Transform the x or y coordinate of a position in the drawing region into a value.

Parameters:

axisId Axis index
pos position

Returns:

Position as axis coordinate

Warning:

The position can be an x or a y coordinate, depending on the specified axis.

A signal indicating, that an item has been attached/detached

Parameters:

plotItem Plot item
on Attached/Detached

Build an information, that can be used to identify a plot item on the legend. The default implementation simply wraps the plot item into a QVariant object. When overloading itemToInfo() usually infoToItem() needs to reimplemeted too.

QVariant itemInfo;
qVariantSetValue( itemInfo, plotItem );

Parameters:

plotItem Plot item

Returns:

Plot item embedded in a QVariant

See also:

infoToItem()

QwtAbstractLegend * QwtPlot::legend ()

Returns:

the plot's legend

See also:

insertLegend()

const QwtAbstractLegend * QwtPlot::legend () const

Returns:

the plot's legend

See also:

insertLegend()

A signal with the attributes how to update the legend entries for a plot item.

Parameters:

itemInfo Info about a plot item, build from itemToInfo()
data Attributes of the entries ( usually <= 1 ) for the plot item.

See also:

itemToInfo(), infoToItem(), QwtAbstractLegend::updateLegend()

QwtPlotLayout * QwtPlot::plotLayout ()

Returns:

the plot's layout

const QwtPlotLayout * QwtPlot::plotLayout () const

Returns:

the plot's layout

Redraw the plot. If the autoReplot option is not set (which is the default) or if any curves are attached to raw data, the plot has to be refreshed explicitly in order to make changes visible.

See also:

updateAxes(), setAutoReplot()

Resize and update internal layout

Parameters:

e Resize event

Set or reset the autoReplot option. If the autoReplot option is set, the plot will be updated implicitly by manipulating member functions. Since this may be time-consuming, it is recommended to leave this option switched off and call replot() explicitly if necessary.

The autoReplot option is set to false by default, which means that the user has to call replot() in order to make changes visible.

Parameters:

tf true or false. Defaults to true.

See also:

replot()

Enable autoscaling for a specified axis. This member function is used to switch back to autoscaling mode after a fixed scale has been set. Autoscaling is enabled by default.

Parameters:

axisId Axis index
on On/Off

See also:

setAxisScale(), setAxisScaleDiv(), updateAxes()

Note:

The autoscaling flag has no effect until updateAxes() is executed ( called by replot() ).

Change the font of an axis.

Parameters:

axisId Axis index
font Font

Warning:

This function changes the font of the tick labels, not of the axis title.

Change the alignment of the tick labels

Parameters:

axisId Axis index
alignment Or'd Qt::AlignmentFlags see <qnamespace.h>

See also:

QwtScaleDraw::setLabelAlignment()

Rotate all tick labels

Parameters:

axisId Axis index
rotation Angle in degrees. When changing the label rotation, the label alignment might be adjusted too.

See also:

QwtScaleDraw::setLabelRotation(), setAxisLabelAlignment()

Set the maximum number of major scale intervals for a specified axis

Parameters:

axisId Axis index
maxMajor Maximum number of major steps

See also:

axisMaxMajor()

Set the maximum number of minor scale intervals for a specified axis

Parameters:

axisId Axis index
maxMinor Maximum number of minor steps

See also:

axisMaxMinor()

Disable autoscaling and specify a fixed scale for a selected axis. In updateAxes() the scale engine calculates a scale division from the specified parameters, that will be assigned to the scale widget. So updates of the scale widget usually happen delayed with the next replot.

Parameters:

axisId Axis index
min Minimum of the scale
max Maximum of the scale
stepSize Major step size. If step == 0, the step size is calculated automatically using the maxMajor setting.

See also:

setAxisMaxMajor(), setAxisAutoScale(), axisStepSize(), QwtScaleEngine::divideScale()

Disable autoscaling and specify a fixed scale for a selected axis. The scale division will be stored locally only until the next call of updateAxes(). So updates of the scale widget usually happen delayed with the next replot.

Parameters:

axisId Axis index
scaleDiv Scale division

See also:

setAxisScale(), setAxisAutoScale()

Set a scale draw.

Parameters:

axisId Axis index
scaleDraw Object responsible for drawing scales.

By passing scaleDraw it is possible to extend QwtScaleDraw functionality and let it take place in QwtPlot. Please note that scaleDraw has to be created with new and will be deleted by the corresponding QwtScale member ( like a child object ).

See also:

QwtScaleDraw, QwtScaleWidget

Warning:

The attributes of scaleDraw will be overwritten by those of the previous QwtScaleDraw.

Change the scale engine for an axis

Parameters:

axisId Axis index
scaleEngine Scale engine

See also:

axisScaleEngine()

Change the title of a specified axis.

Parameters:

axisId Axis index
title axis title

Change the title of a specified axis.

Parameters:

axisId Axis index
title Axis title

Set the drawing canvas of the plot widget. QwtPlot invokes methods of the canvas as meta methods ( see QMetaObject ). In opposite to using conventional C++ techniques like virtual methods they allow to use canvas implementations that are derived from QWidget or QGLWidget.

The following meta methods could be implemented:

  • replot() When the canvas doesn't offer a replot method, QwtPlot calls update() instead.
  • borderPath() The border path is necessary to clip the content of the canvas When the canvas doesn't have any special border ( f.e rounded corners ) it is o.k. not to implement this method.

The default canvas is a QwtPlotCanvas

Parameters:

canvas Canvas Widget

See also:

canvas()

Change the background of the plotting area. Sets brush to QPalette::Window of all color groups of the palette of the canvas. Using canvas()->setPalette() is a more powerful way to set these colors.

Parameters:

brush New background brush

See also:

canvasBackground()

Change the text the footer

Parameters:

text New text of the footer

Change the text the footer

Parameters:

text New text of the footer

Assign a new plot layout.

Parameters:

layout Layout()

See also:

plotLayout()

Change the plot's title

Parameters:

title New title

Change the plot's title

Parameters:

title New title

Returns:

Size hint for the plot widget

See also:

minimumSizeHint()

QwtText QwtPlot::title () const

Returns:

Title of the plot

QwtTextLabel * QwtPlot::titleLabel ()

Returns:

Title label widget.

const QwtTextLabel * QwtPlot::titleLabel () const

Returns:

Title label widget.

Transform a value into a coordinate in the plotting region.

Parameters:

axisId Axis index
value value

Returns:

X or Y coordinate in the plotting region corresponding to the value.

Rebuild the axes scales. In case of autoscaling the boundaries of a scale are calculated from the bounding rectangles of all plot items, having the QwtPlotItem::AutoScale flag enabled ( QwtScaleEngine::autoScale() ). Then a scale division is calculated ( QwtScaleEngine::didvideScale() ) and assigned to scale widget.

When the scale boundaries have been assigned with setAxisScale() a scale division is calculated ( QwtScaleEngine::didvideScale() ) for this interval and assigned to the scale widget.

When the scale has been set explicitly by setAxisScaleDiv() the locally stored scale division gets assigned to the scale widget.

The scale widget indicates modifications by emitting a QwtScaleWidget::scaleDivChanged() signal.

updateAxes() is usually called by replot().

See also:

setAxisAutoScale(), setAxisScale(), setAxisScaleDiv(), replot() QwtPlotItem::boundingRect()

Update the canvas margins. Plot items might indicate, that they need some extra space at the borders of the canvas by the QwtPlotItem::Margins flag.

getCanvasMarginsHint(), QwtPlotItem::getCanvasMarginHint()

Adjust plot content to its current size.

See also:

resizeEvent()

Emit legendDataChanged() for all plot item

See also:

QwtPlotItem::legendData(), legendDataChanged()

Emit legendDataChanged() for a plot item

Parameters:

plotItem Plot item

See also:

QwtPlotItem::legendData(), legendDataChanged()

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Wed Jan 2 2019 Version 6.1.4