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QCPItemTracer Class Reference

Item that sticks to QCPGraph data points. More...

Inheritance diagram for QCPItemTracer:
Inheritance graph

Public Types

enum  TracerStyle

Public Functions

 QCPItemTracer (QCustomPlot *parentPlot)
QPen pen () const
QPen selectedPen () const
QBrush brush () const
QBrush selectedBrush () const
double size () const
TracerStyle style () const
QCPGraphgraph () const
double graphKey () const
bool interpolating () const
void setPen (const QPen &pen)
void setSelectedPen (const QPen &pen)
void setBrush (const QBrush &brush)
void setSelectedBrush (const QBrush &brush)
void setSize (double size)
void setStyle (TracerStyle style)
void setGraph (QCPGraph *graph)
void setGraphKey (double key)
void setInterpolating (bool enabled)
virtual double selectTest (const QPointF &pos, bool onlySelectable, QVariant *details=nullptr) const
void updatePosition ()
- Public Functions inherited from QCPAbstractItem
 QCPAbstractItem (QCustomPlot *parentPlot)
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)
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 Functions inherited from QCPLayerable
 QCPLayerable (QCustomPlot *plot, QString targetLayer=QString(), QCPLayerable *parentLayerable=nullptr)
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

Public Members

QCPItemPosition *const position

Protected Functions

virtual void draw (QCPPainter *painter)
QPen mainPen () const
QBrush mainBrush () const
- Protected Functions inherited from QCPAbstractItem
virtual QCP::Interaction selectionCategory () const
virtual QRect clipRect () const
virtual void applyDefaultAntialiasingHint (QCPPainter *painter) const
virtual void selectEvent (QMouseEvent *event, bool additive, const QVariant &details, bool *selectionStateChanged)
virtual void deselectEvent (bool *selectionStateChanged)
virtual QPointF anchorPixelPosition (int anchorId) const
double rectDistance (const QRectF &rect, const QPointF &pos, bool filledRect) const
QCPItemPositioncreatePosition (const QString &name)
QCPItemAnchorcreateAnchor (const QString &name, int anchorId)
- Protected Functions inherited from QCPLayerable
virtual void parentPlotInitialized (QCustomPlot *parentPlot)
virtual void mousePressEvent (QMouseEvent *event, const QVariant &details)
virtual void mouseMoveEvent (QMouseEvent *event, const QPointF &startPos)
virtual void mouseReleaseEvent (QMouseEvent *event, const QPointF &startPos)
virtual void mouseDoubleClickEvent (QMouseEvent *event, const QVariant &details)
virtual void wheelEvent (QWheelEvent *event)
void initializeParentPlot (QCustomPlot *parentPlot)
void setParentLayerable (QCPLayerable *parentLayerable)
bool moveToLayer (QCPLayer *layer, bool prepend)
void applyAntialiasingHint (QCPPainter *painter, bool localAntialiased, QCP::AntialiasedElement overrideElement) const

Additional Inherited Members

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

Detailed Description

Item that sticks to QCPGraph data points.

Tracer example. Blue dotted circles are anchors, solid blue discs are positions.

The tracer can be connected with a QCPGraph via setGraph. Then it will automatically adopt the coordinate axes of the graph and update its position to be on the graph's data. This means the key stays controllable via setGraphKey, but the value will follow the graph data. If a QCPGraph is connected, note that setting the coordinates of the tracer item directly via position will have no effect because they will be overriden in the next redraw (this is when the coordinate update happens).

If the specified key in setGraphKey is outside the key bounds of the graph, the tracer will stay at the corresponding end of the graph.

With setInterpolating you may specify whether the tracer may only stay exactly on data points or whether it interpolates data points linearly, if given a key that lies between two data points of the graph.

The tracer has different visual styles, see setStyle. It is also possible to make the tracer have no own visual appearance (set the style to tsNone), and just connect other item positions to the tracer position (used as an anchor) via QCPItemPosition::setParentAnchor.

The tracer position is only automatically updated upon redraws. So when the data of the graph changes and immediately afterwards (without a redraw) the position coordinates of the tracer are retrieved, they will not reflect the updated data of the graph. In this case updatePosition must be called manually, prior to reading the tracer coordinates.

Member Enumeration Documentation

§ TracerStyle

The different visual appearances a tracer item can have. Some styles size may be controlled with setSize.

See also

The tracer is not visible.


A plus shaped crosshair with limited size.


A plus shaped crosshair which spans the complete axis rect.


A circle.


A square.

Constructor & Destructor Documentation

§ QCPItemTracer()

QCPItemTracer::QCPItemTracer ( QCustomPlot parentPlot)

Creates a tracer item and sets default values.

The created item is automatically registered with parentPlot. This QCustomPlot instance takes ownership of the item, so do not delete it manually but use QCustomPlot::removeItem() instead.

Member Function Documentation

§ setPen()

void QCPItemTracer::setPen ( const QPen &  pen)

Sets the pen that will be used to draw the line of the tracer

See also
setSelectedPen, setBrush

§ setSelectedPen()

void QCPItemTracer::setSelectedPen ( const QPen &  pen)

Sets the pen that will be used to draw the line of the tracer when selected

See also
setPen, setSelected

§ setBrush()

void QCPItemTracer::setBrush ( const QBrush &  brush)

Sets the brush that will be used to draw any fills of the tracer

See also
setSelectedBrush, setPen

§ setSelectedBrush()

void QCPItemTracer::setSelectedBrush ( const QBrush &  brush)

Sets the brush that will be used to draw any fills of the tracer, when selected.

See also
setBrush, setSelected

§ setSize()

void QCPItemTracer::setSize ( double  size)

Sets the size of the tracer in pixels, if the style supports setting a size (e.g. tsSquare does, tsCrosshair does not).

§ setStyle()

void QCPItemTracer::setStyle ( QCPItemTracer::TracerStyle  style)

Sets the style/visual appearance of the tracer.

If you only want to use the tracer position as an anchor for other items, set style to tsNone.

§ setGraph()

void QCPItemTracer::setGraph ( QCPGraph graph)

Sets the QCPGraph this tracer sticks to. The tracer position will be set to type QCPItemPosition::ptPlotCoords and the axes will be set to the axes of graph.

To free the tracer from any graph, set graph to nullptr. The tracer position can then be placed freely like any other item position. This is the state the tracer will assume when its graph gets deleted while still attached to it.

See also

§ setGraphKey()

void QCPItemTracer::setGraphKey ( double  key)

Sets the key of the graph's data point the tracer will be positioned at. This is the only free coordinate of a tracer when attached to a graph.

Depending on setInterpolating, the tracer will be either positioned on the data point closest to key, or will stay exactly at key and interpolate the value linearly.

See also
setGraph, setInterpolating

§ setInterpolating()

void QCPItemTracer::setInterpolating ( bool  enabled)

Sets whether the value of the graph's data points shall be interpolated, when positioning the tracer.

If enabled is set to false and a key is given with setGraphKey, the tracer is placed on the data point of the graph which is closest to the key, but which is not necessarily exactly there. If enabled is true, the tracer will be positioned exactly at the specified key, and the appropriate value will be interpolated from the graph's data points linearly.

See also
setGraph, setGraphKey

§ selectTest()

double QCPItemTracer::selectTest ( const QPointF &  pos,
bool  onlySelectable,
QVariant *  details = nullptr 
) const

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 object is represented not by single lines but by an area like a QCPItemText or the bars of a QCPBars plottable, a click inside the area should also be considered a hit. In these cases this function thus returns a constant value greater zero but still below the parent plot's selection tolerance. (typically the selectionTolerance multiplied by 0.99).

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.

In the case of 1D Plottables (QCPAbstractPlottable1D, like QCPGraph or QCPBars) details will be set to a QCPDataSelection, describing the closest data point to pos.

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

See also
selectEvent, deselectEvent, mousePressEvent, wheelEvent, QCustomPlot::setInteractions, QCPAbstractPlottable1D::selectTestRect

Implements QCPAbstractItem.

§ updatePosition()

void QCPItemTracer::updatePosition ( )

If the tracer is connected with a graph (setGraph), this function updates the tracer's position to reside on the graph data, depending on the configured key (setGraphKey).

It is called automatically on every redraw and normally doesn't need to be called manually. One exception is when you want to read the tracer coordinates via position and are not sure that the graph's data (or the tracer key with setGraphKey) hasn't changed since the last redraw. In that situation, call this function before accessing position, to make sure you don't get out-of-date coordinates.

If there is no graph set on this tracer, this function does nothing.

§ draw()

void QCPItemTracer::draw ( QCPPainter painter)

Draws this item with the provided painter.

The cliprect of the provided painter is set to the rect returned by clipRect before this function is called. The clipRect depends on the clipping settings defined by setClipToAxisRect and setClipAxisRect.

Implements QCPAbstractItem.

§ mainPen()

QPen QCPItemTracer::mainPen ( ) const

Returns the pen that should be used for drawing lines. Returns mPen when the item is not selected and mSelectedPen when it is.

§ mainBrush()

QBrush QCPItemTracer::mainBrush ( ) const

Returns the brush that should be used for drawing fills of the item. Returns mBrush when the item is not selected and mSelectedBrush when it is.

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