Vespucci  1.0.0
QCPAbstractItem Class Referenceabstract

The abstract base class for all items in a plot. More...

#include <qcustomplot.h>

Inheritance diagram for QCPAbstractItem:
QCPLayerable QCPItemBracket QCPItemCurve QCPItemEllipse QCPItemLine QCPItemPixmap QCPItemRect QCPItemStraightLine QCPItemText QCPItemTracer


void selectionChanged (bool selected)
void selectableChanged (bool selectable)
- Signals inherited from QCPLayerable
void layerChanged (QCPLayer *newLayer)

Public Member Functions

 QCPAbstractItem (QCustomPlot *parentPlot)
virtual ~QCPAbstractItem ()
bool clipToAxisRect () const
QCPAxisRectclipAxisRect () const
bool selectable () const
bool selected () const
void setClipToAxisRect (bool clip)
void setClipAxisRect (QCPAxisRect *rect)
Q_SLOT void setSelectable (bool selectable)
Q_SLOT void setSelected (bool selected)
virtual double selectTest (const QPointF &pos, bool onlySelectable, QVariant *details=0) const =0
QList< QCPItemPosition * > positions () const
QList< QCPItemAnchor * > anchors () const
QCPItemPositionposition (const QString &name) const
QCPItemAnchoranchor (const QString &name) const
bool hasAnchor (const QString &name) const
- Public Member Functions inherited from QCPLayerable
 QCPLayerable (QCustomPlot *plot, QString targetLayer=QString(), QCPLayerable *parentLayerable=0)
 ~QCPLayerable ()
bool visible () const
QCustomPlotparentPlot () const
QCPLayerableparentLayerable () const
QCPLayerlayer () const
bool antialiased () const
void setVisible (bool on)
Q_SLOT bool setLayer (QCPLayer *layer)
bool setLayer (const QString &layerName)
void setAntialiased (bool enabled)
bool realVisibility () const

Protected Member Functions

virtual QCP::Interaction selectionCategory () const
virtual QRect clipRect () const
virtual void applyDefaultAntialiasingHint (QCPPainter *painter) const
virtual void draw (QCPPainter *painter)=0
virtual void selectEvent (QMouseEvent *event, bool additive, const QVariant &details, bool *selectionStateChanged)
virtual void deselectEvent (bool *selectionStateChanged)
virtual QPointF anchorPixelPoint (int anchorId) const
double distSqrToLine (const QPointF &start, const QPointF &end, const QPointF &point) const
double rectSelectTest (const QRectF &rect, const QPointF &pos, bool filledRect) const
QCPItemPositioncreatePosition (const QString &name)
QCPItemAnchorcreateAnchor (const QString &name, int anchorId)
- Protected Member Functions inherited from QCPLayerable
virtual void parentPlotInitialized (QCustomPlot *parentPlot)
void initializeParentPlot (QCustomPlot *parentPlot)
void setParentLayerable (QCPLayerable *parentLayerable)
bool moveToLayer (QCPLayer *layer, bool prepend)
void applyAntialiasingHint (QCPPainter *painter, bool localAntialiased, QCP::AntialiasedElement overrideElement) const

Protected Attributes

bool mClipToAxisRect
QPointer< QCPAxisRectmClipAxisRect
QList< QCPItemPosition * > mPositions
QList< QCPItemAnchor * > mAnchors
bool mSelectable
bool mSelected
- Protected Attributes inherited from QCPLayerable
bool mVisible
QPointer< QCPLayerablemParentLayerable
bool mAntialiased


class QCustomPlot
class QCPItemAnchor

Detailed Description

The abstract base class for all items in a plot.

In QCustomPlot, items are supplemental graphical elements that are neither plottables (QCPAbstractPlottable) nor axes (QCPAxis). While plottables are always tied to two axes and thus plot coordinates, items can also be placed in absolute coordinates independent of any axes. Each specific item has at least one QCPItemPosition member which controls the positioning. Some items are defined by more than one coordinate and thus have two or more QCPItemPosition members (For example, QCPItemRect has topLeft and bottomRight).

This abstract base class defines a very basic interface like visibility and clipping. Since this class is abstract, it can't be instantiated. Use one of the subclasses or create a subclass yourself to create new items.

The built-in items are:

QCPItemLineA line defined by a start and an end point. May have different ending styles on each side (e.g. arrows).
QCPItemStraightLineA straight line defined by a start and a direction point. Unlike QCPItemLine, the straight line is infinitely long and has no endings.
QCPItemCurveA curve defined by start, end and two intermediate control points. May have different ending styles on each side (e.g. arrows).
QCPItemRectA rectangle
QCPItemEllipseAn ellipse
QCPItemPixmapAn arbitrary pixmap
QCPItemTextA text label
QCPItemBracketA bracket which may be used to reference/highlight certain parts in the plot.
QCPItemTracerAn item that can be attached to a QCPGraph and sticks to its data points, given a key coordinate.


Items are by default clipped to the main axis rect (they are only visible inside the axis rect). To make an item visible outside that axis rect, disable clipping via setClipToAxisRect(false).

On the other hand if you want the item to be clipped to a different axis rect, specify it via setClipAxisRect. This clipAxisRect property of an item is only used for clipping behaviour, and in principle is independent of the coordinate axes the item might be tied to via its position members (QCPItemPosition::setAxes). However, it is common that the axis rect for clipping also contains the axes used for the item positions.

Using items

First you instantiate the item you want to use and add it to the plot:

QCPItemLine *line = new QCPItemLine(customPlot);

by default, the positions of the item are bound to the x- and y-Axis of the plot. So we can just set the plot coordinates where the line should start/end:

line->start->setCoords(-0.1, 0.8);
line->end->setCoords(1.1, 0.2);

If we don't want the line to be positioned in plot coordinates but a different coordinate system, e.g. absolute pixel positions on the QCustomPlot surface, we need to change the position type like this:

Then we can set the coordinates, this time in pixels:

line->start->setCoords(100, 200);
line->end->setCoords(450, 320);

and make the line visible on the entire QCustomPlot, by disabling clipping to the axis rect:


For more advanced plots, it is even possible to set different types and parent anchors per X/Y coordinate of an item position, using for example QCPItemPosition::setTypeX or QCPItemPosition::setParentAnchorX. For details, see the documentation of QCPItemPosition.

Creating own items

To create an own item, you implement a subclass of QCPAbstractItem. These are the pure virtual functions, you must implement:

See the documentation of those functions for what they need to do.

Allowing the item to be positioned

As mentioned, item positions are represented by QCPItemPosition members. Let's assume the new item shall have only one point as its position (as opposed to two like a rect or multiple like a polygon). You then add a public member of type QCPItemPosition like so:

QCPItemPosition * const myPosition;

the const makes sure the pointer itself can't be modified from the user of your new item (the QCPItemPosition instance it points to, can be modified, of course). The initialization of this pointer is made easy with the createPosition function. Just assign the return value of this function to each QCPItemPosition in the constructor of your item. createPosition takes a string which is the name of the position, typically this is identical to the variable name. For example, the constructor of QCPItemExample could look like this:

QCPItemExample::QCPItemExample(QCustomPlot *parentPlot) :
// other constructor code

The draw function

To give your item a visual representation, reimplement the draw function and use the passed QCPPainter to draw the item. You can retrieve the item position in pixel coordinates from the position member(s) via QCPItemPosition::pixelPoint.

To optimize performance you should calculate a bounding rect first (don't forget to take the pen width into account), check whether it intersects the clipRect, and only draw the item at all if this is the case.

The selectTest function

Your implementation of the selectTest function may use the helpers distSqrToLine and rectSelectTest. With these, the implementation of the selection test becomes significantly simpler for most items. See the documentation of selectTest for what the function parameters mean and what the function should return.

Providing anchors

Providing anchors (QCPItemAnchor) starts off like adding a position. First you create a public member, e.g.

QCPItemAnchor * const bottom;

and create it in the constructor with the createAnchor function, assigning it a name and an anchor id (an integer enumerating all anchors on the item, you may create an own enum for this). Since anchors can be placed anywhere, relative to the item's position(s), your item needs to provide the position of every anchor with the reimplementation of the anchorPixelPoint(int anchorId) function.

In essence the QCPItemAnchor is merely an intermediary that itself asks your item for the pixel position when anything attached to the anchor needs to know the coordinates.

Definition at line 1612 of file qcustomplot.h.

Constructor & Destructor Documentation

QCPAbstractItem::QCPAbstractItem ( QCustomPlot parentPlot)

Base class constructor which initializes base class members.

Definition at line 8360 of file qcustomplot.cpp.

QCPAbstractItem::~QCPAbstractItem ( )

Definition at line 8374 of file qcustomplot.cpp.

Member Function Documentation

QCPItemAnchor * QCPAbstractItem::anchor ( const QString &  name) const

Returns the QCPItemAnchor with the specified name. If this item doesn't have an anchor by that name, returns 0.

This function provides an alternative way to access item anchors. Normally, you access anchors direcly by their member pointers (which typically have the same variable name as name).

See also
anchors, position

Definition at line 8484 of file qcustomplot.cpp.

QPointF QCPAbstractItem::anchorPixelPoint ( int  anchorId) const

Reimplemented in QCPItemBracket, QCPItemPixmap, QCPItemEllipse, QCPItemText, and QCPItemRect.

Definition at line 8634 of file qcustomplot.cpp.

QList< QCPItemAnchor * > QCPAbstractItem::anchors ( ) const

Returns all anchors of the item in a list. Note that since a position (QCPItemPosition) is always also an anchor, the list will also contain the positions of this item.

See also
positions, anchor

Definition at line 1642 of file qcustomplot.h.

void QCPAbstractItem::applyDefaultAntialiasingHint ( QCPPainter painter) const

Implements QCPLayerable.

Definition at line 8543 of file qcustomplot.cpp.

QCPAxisRect * QCPAbstractItem::clipAxisRect ( ) const

Definition at line 8381 of file qcustomplot.cpp.

QRect QCPAbstractItem::clipRect ( ) const

Reimplemented from QCPLayerable.

Definition at line 8522 of file qcustomplot.cpp.

bool QCPAbstractItem::clipToAxisRect ( ) const

Definition at line 1626 of file qcustomplot.h.

QCPItemAnchor * QCPAbstractItem::createAnchor ( const QString &  name,
int  anchorId 

Definition at line 8688 of file qcustomplot.cpp.

QCPItemPosition * QCPAbstractItem::createPosition ( const QString &  name)

Definition at line 8654 of file qcustomplot.cpp.

void QCPAbstractItem::deselectEvent ( bool *  selectionStateChanged)

Reimplemented from QCPLayerable.

Definition at line 8712 of file qcustomplot.cpp.

double QCPAbstractItem::distSqrToLine ( const QPointF &  start,
const QPointF &  end,
const QPointF &  point 
) const

Definition at line 8560 of file qcustomplot.cpp.

void QCPAbstractItem::draw ( QCPPainter painter)
protectedpure virtual
bool QCPAbstractItem::hasAnchor ( const QString &  name) const

Returns whether this item has an anchor with the specified name.

Note that you can check for positions with this function, too. This is because every position is also an anchor (QCPItemPosition inherits from QCPItemAnchor).

See also
anchor, position

Definition at line 8503 of file qcustomplot.cpp.

QCPItemPosition * QCPAbstractItem::position ( const QString &  name) const

Returns the QCPItemPosition with the specified name. If this item doesn't have a position by that name, returns 0.

This function provides an alternative way to access item positions. Normally, you access positions direcly by their member pointers (which typically have the same variable name as name).

See also
positions, anchor

Definition at line 8463 of file qcustomplot.cpp.

QList< QCPItemPosition * > QCPAbstractItem::positions ( ) const

Returns all positions of the item in a list.

See also
anchors, position

Definition at line 1641 of file qcustomplot.h.

double QCPAbstractItem::rectSelectTest ( const QRectF &  rect,
const QPointF &  pos,
bool  filledRect 
) const

Definition at line 8598 of file qcustomplot.cpp.

bool QCPAbstractItem::selectable ( ) const

Definition at line 1628 of file qcustomplot.h.

void QCPAbstractItem::selectableChanged ( bool  selectable)
bool QCPAbstractItem::selected ( ) const

Definition at line 1629 of file qcustomplot.h.

void QCPAbstractItem::selectEvent ( QMouseEvent *  event,
bool  additive,
const QVariant &  details,
bool *  selectionStateChanged 

Reimplemented from QCPLayerable.

Definition at line 8698 of file qcustomplot.cpp.

QCP::Interaction QCPAbstractItem::selectionCategory ( ) const

Reimplemented from QCPLayerable.

Definition at line 8724 of file qcustomplot.cpp.

void QCPAbstractItem::selectionChanged ( bool  selected)

This signal is emitted when the selection state of this item has changed, either by user interaction or by a direct call to setSelected.

virtual double QCPAbstractItem::selectTest ( const QPointF &  pos,
bool  onlySelectable,
QVariant *  details = 0 
) const
pure virtual

This function is used to decide whether a click hits a layerable object or not.

pos is a point in pixel coordinates on the QCustomPlot surface. This function returns the shortest pixel distance of this point to the object. If the object is either invisible or the distance couldn't be determined, -1.0 is returned. Further, if onlySelectable is true and the object is not selectable, -1.0 is returned, too.

If the item is represented not by single lines but by an area like QCPItemRect or QCPItemText, a click inside the area returns a constant value greater zero (typically the selectionTolerance of the parent QCustomPlot multiplied by 0.99). If the click lies outside the area, this function returns -1.0.

Providing a constant value for area objects allows selecting line objects even when they are obscured by such area objects, by clicking close to the lines (i.e. closer than 0.99*selectionTolerance).

The actual setting of the selection state is not done by this function. This is handled by the parent QCustomPlot when the mouseReleaseEvent occurs, and the finally selected object is notified via the selectEvent/deselectEvent methods.

details is an optional output parameter. Every layerable subclass may place any information in details. This information will be passed to selectEvent when the parent QCustomPlot decides on the basis of this selectTest call, that the object was successfully selected. The subsequent call to selectEvent will carry the details. This is useful for multi-part objects (like QCPAxis). This way, a possibly complex calculation to decide which part was clicked is only done once in selectTest. The result (i.e. the actually clicked part) can then be placed in details. So in the subsequent selectEvent, the decision which part was selected doesn't have to be done a second time for a single selection operation.

You may pass 0 as details to indicate that you are not interested in those selection details.

See also
selectEvent, deselectEvent, QCustomPlot::setInteractions

Reimplemented from QCPLayerable.

Implemented in QCPItemBracket, QCPItemTracer, QCPItemPixmap, QCPItemEllipse, QCPItemText, QCPItemRect, QCPItemCurve, QCPItemLine, and QCPItemStraightLine.

void QCPAbstractItem::setClipAxisRect ( QCPAxisRect rect)

Sets the clip axis rect. It defines the rect that will be used to clip the item when setClipToAxisRect is set to true.

See also

Definition at line 8405 of file qcustomplot.cpp.

void QCPAbstractItem::setClipToAxisRect ( bool  clip)

Sets whether the item shall be clipped to an axis rect or whether it shall be visible on the entire QCustomPlot. The axis rect can be set with setClipAxisRect.

See also

Definition at line 8392 of file qcustomplot.cpp.

void QCPAbstractItem::setSelectable ( bool  selectable)

Sets whether the user can (de-)select this item by clicking on the QCustomPlot surface. (When QCustomPlot::setInteractions contains QCustomPlot::iSelectItems.)

However, even when selectable was set to false, it is possible to set the selection manually, by calling setSelected.

See also
QCustomPlot::setInteractions, setSelected

Definition at line 8421 of file qcustomplot.cpp.

void QCPAbstractItem::setSelected ( bool  selected)

Sets whether this item is selected or not. When selected, it might use a different visual appearance (e.g. pen and brush), this depends on the specific item though.

The entire selection mechanism for items is handled automatically when QCustomPlot::setInteractions contains QCustomPlot::iSelectItems. You only need to call this function when you wish to change the selection state manually.

This function can change the selection state even when setSelectable was set to false.

emits the selectionChanged signal when selected is different from the previous selection state.

See also
setSelectable, selectTest

Definition at line 8444 of file qcustomplot.cpp.

Friends And Related Function Documentation

friend class QCPItemAnchor

Definition at line 1681 of file qcustomplot.h.

friend class QCustomPlot

Definition at line 1680 of file qcustomplot.h.

Member Data Documentation

QList<QCPItemAnchor*> QCPAbstractItem::mAnchors

Definition at line 1656 of file qcustomplot.h.

QPointer<QCPAxisRect> QCPAbstractItem::mClipAxisRect

Definition at line 1654 of file qcustomplot.h.

bool QCPAbstractItem::mClipToAxisRect

Definition at line 1653 of file qcustomplot.h.

QList<QCPItemPosition*> QCPAbstractItem::mPositions

Definition at line 1655 of file qcustomplot.h.

bool QCPAbstractItem::mSelectable

Definition at line 1657 of file qcustomplot.h.

bool QCPAbstractItem::mSelected

Definition at line 1657 of file qcustomplot.h.

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