QwtPlotAxisWheelInteraction Class Reference

Configurable wheel interaction for a single plot axis. More...

#include <qwt_plot_axis_wheel_interaction.h>

Inheritance diagram for QwtPlotAxisWheelInteraction:

Classes
class	PrivateData

Public Member Functions
	QwtPlotAxisWheelInteraction (QwtPlot *plot, QwtAxisId axisId)
	Constructor from plot and axis id.
	QwtPlotAxisWheelInteraction (QwtScaleWidget *scaleWidget)
void	setEnabled (bool on)
	Enable or disable the interaction.
bool	isEnabled () const
	Return whether the interaction is enabled.
void	setZoomModifiers (Qt::KeyboardModifiers modifiers)
	Set keyboard modifiers for zoom mode.
Qt::KeyboardModifiers	zoomModifiers () const
	Return the zoom modifiers.
void	setZoomFactor (double factor)
	Set the zoom factor per wheel step.
double	zoomFactor () const
	Return the zoom factor.
void	setPanModifiers (Qt::KeyboardModifiers modifiers)
	Set keyboard modifiers for pan mode.
Qt::KeyboardModifiers	panModifiers () const
	Return the pan modifiers.
void	setPanFactor (int pixelsPerStep)
	Set the pan distance per wheel step.
int	panFactor () const
	Return the pan factor in pixels.
QwtScaleWidget *	scaleWidget ()
	Return the observed scale widget.
const QwtScaleWidget *	scaleWidget () const
	Return the observed scale widget (const version)
QwtPlot *	plot ()
	Return the plot that owns the axis.
const QwtPlot *	plot () const
	Return the plot that owns the axis (const version)
QwtAxisId	axisId () const
	Return the axis id.

Protected Member Functions
virtual bool	eventFilter (QObject *obj, QEvent *event) override
	Event filter for wheel events on the scale widget.
virtual bool	handleWheelEvent (QWheelEvent *event)
	Handle a wheel event on the scale widget.
virtual void	wheelZoom (double factor, const QPoint &cursorPos)
	Perform a zoom on the axis.
virtual void	wheelPan (int deltaPixels)
	Perform a pan on the axis.

Detailed Description

Configurable wheel interaction for a single plot axis.

QwtPlotAxisWheelInteraction installs an event filter on a QwtScaleWidget (the axis tick area) and provides two configurable wheel actions:

• Zoom (plain wheel by default): zooms the axis centered at the cursor position using QwtPlot::zoomAxis().
• Pan (Ctrl+wheel by default): pans the axis by a fixed pixel amount per step using QwtPlot::panAxis().

Unlike the built-in QwtPlotScaleEventDispatcher (which hardcodes wheel=zoom and requires the axis to be clicked/selected first), this class:

• Supports keyboard modifiers to switch between zoom and pan.
• Works immediately without needing to select the axis first.
• Is fully configurable (modifiers, factors, enable/disable).
• Is designed for inheritance — override wheelZoom(), wheelPan(), or handleWheelEvent() to implement custom behavior.

When the modifier matches zoom or pan, the event is consumed (return true) so the dispatcher does not also process it. When the modifier matches neither, the event is passed through to the dispatcher for default handling.

Typical usage:

// Plain wheel zooms XBottom at cursor; Ctrl+wheel pans it
new QwtPlotAxisWheelInteraction(plot, QwtAxis::XBottom);
 
// Customize: Shift+wheel zooms YLeft, plain wheel pans
auto* ix = new QwtPlotAxisWheelInteraction(plot, QwtAxis::YLeft);
ix->setZoomModifiers(Qt::ShiftModifier);
ix->setPanModifiers(Qt::NoModifier);

Inheritance example:

class CenterZoom : public QwtPlotAxisWheelInteraction {
public:
    using QwtPlotAxisWheelInteraction::QwtPlotAxisWheelInteraction;
protected:
    void wheelZoom(double factor, const QPoint&) override {
        // Zoom centered on axis midpoint instead of cursor
        const QwtScaleMap m = plot()->canvasMap(axisId());
        const int mid = static_cast<int>((m.p1() + m.p2()) / 2);
        QwtPlotAxisWheelInteraction::wheelZoom(factor, QPoint(mid, 0));
    }
};

See also

QwtPlotScaleEventDispatcher, QwtPlot::zoomAxis(), QwtPlot::panAxis()

Constructor & Destructor Documentation

QwtPlotAxisWheelInteraction()

QwtPlotAxisWheelInteraction::QwtPlotAxisWheelInteraction ( QwtPlot *  plot, QwtAxisId  axisId  )

explicit

Constructor from plot and axis id.

Parameters

[in]	plot	The plot that owns the axis
[in]	axisId	The axis to attach the interaction to

The event filter is installed on the QwtScaleWidget for the given axis. The interaction is enabled by default.

Constructor from a scale widget

Parameters

[in]

scaleWidget

The axis scale widget to observe

The plot and axis id are auto-derived from the scale widget's parent (which must be a QwtPlot) using QwtPlotScaleEventDispatcher::findAxisIdByScaleWidget().

Destructor

Member Function Documentation

axisId()

QwtAxisId QwtPlotAxisWheelInteraction::axisId

(

)

const

Return the axis id.

Returns

Axis identifier

eventFilter()

bool QwtPlotAxisWheelInteraction::eventFilter ( QObject *  obj, QEvent *  event  )

overrideprotectedvirtual

Event filter for wheel events on the scale widget.

Parameters

[in]	obj	Object receiving the event (should be the scale widget)
[in]	event	Event

Returns

true when the wheel event was handled (consumed), false otherwise

See also

handleWheelEvent()

handleWheelEvent()

bool QwtPlotAxisWheelInteraction::handleWheelEvent ( QWheelEvent *  event )

protectedvirtual

Handle a wheel event on the scale widget.

The wheel delta is read via qwt::compat::wheelEventDelta() for Qt5/Qt6 compatibility. When the current modifiers match the zoom modifiers, wheelZoom() is called. When they match the pan modifiers, wheelPan() is called. Otherwise the event is passed through (return false) so the QwtPlotScaleEventDispatcher can handle it.

Parameters

[in]

event

Wheel event

Returns

true if the event was handled, false if modifiers matched neither zoom nor pan mode

isEnabled()

bool QwtPlotAxisWheelInteraction::isEnabled

(

)

const

Return whether the interaction is enabled.

Returns

true when enabled, false otherwise

See also

setEnabled()

panFactor()

int QwtPlotAxisWheelInteraction::panFactor

(

)

const

Return the pan factor in pixels.

Returns

Pixels per wheel step

See also

setPanFactor()

panModifiers()

Qt::KeyboardModifiers QwtPlotAxisWheelInteraction::panModifiers

(

)

const

Return the pan modifiers.

Returns

Keyboard modifiers for pan mode

See also

setPanModifiers()

plot() [1/2]

QwtPlot * QwtPlotAxisWheelInteraction::plot

(

)

Return the plot that owns the axis.

Returns

Pointer to the QwtPlot widget

plot() [2/2]

const QwtPlot * QwtPlotAxisWheelInteraction::plot

(

)

const

Return the plot that owns the axis (const version)

Returns

Const pointer to the QwtPlot widget

scaleWidget() [1/2]

QwtScaleWidget * QwtPlotAxisWheelInteraction::scaleWidget

(

)

Return the observed scale widget.

Returns

Pointer to the scale widget

scaleWidget() [2/2]

const QwtScaleWidget * QwtPlotAxisWheelInteraction::scaleWidget

(

)

const

Return the observed scale widget (const version)

Returns

Const pointer to the scale widget

setEnabled()

void QwtPlotAxisWheelInteraction::setEnabled

(

bool

on

)

Enable or disable the interaction.

When enabled, an event filter is installed on the observed scale widget to intercept wheel events before they reach the QwtPlotScaleEventDispatcher. When disabled, the filter is removed and the dispatcher regains full control.

Parameters

[in]

on

true to enable, false to disable

See also

isEnabled(), eventFilter()

setPanFactor()

void QwtPlotAxisWheelInteraction::setPanFactor

(

int

pixelsPerStep

)

Set the pan distance per wheel step.

Parameters

[in]

pixelsPerStep

Number of pixels to pan per wheel notch (default: 30)

See also

panFactor()

setPanModifiers()

void QwtPlotAxisWheelInteraction::setPanModifiers

(

Qt::KeyboardModifiers

modifiers

)

Set keyboard modifiers for pan mode.

When the wheel is rotated with these modifiers on the scale widget, the axis is panned. The default is Qt::ControlModifier.

Parameters

[in]

modifiers

Keyboard modifiers

See also

panModifiers()

setZoomFactor()

void QwtPlotAxisWheelInteraction::setZoomFactor

(

double

factor

)

Set the zoom factor per wheel step.

Values > 1 zoom in (range shrinks), values < 1 zoom out (range expands). The default is 1.2. For multi-step wheels the factor is compounded: pow(zoomFactor, abs(delta/120)).

Parameters

[in]

factor

Zoom factor

See also

zoomFactor()

setZoomModifiers()

void QwtPlotAxisWheelInteraction::setZoomModifiers

(

Qt::KeyboardModifiers

modifiers

)

Set keyboard modifiers for zoom mode.

When the wheel is rotated with these modifiers on the scale widget, the axis is zoomed. The default is Qt::NoModifier (plain wheel).

Parameters

[in]

modifiers

Keyboard modifiers

See also

zoomModifiers()

wheelPan()

void QwtPlotAxisWheelInteraction::wheelPan ( int  deltaPixels )

protectedvirtual

Perform a pan on the axis.

Default implementation calls QwtPlot::panAxis() with the given pixel delta, then replotAll(). Auto-replot is temporarily disabled to avoid redundant repaints.

Override this method to customize pan behavior, e.g. invert direction or add momentum.

Parameters

[in]

deltaPixels

Pixel offset (positive = right/down, negative = left/up)

wheelZoom()

void QwtPlotAxisWheelInteraction::wheelZoom ( double  factor, const QPoint &  cursorPos  )

protectedvirtual

Perform a zoom on the axis.

Default implementation calls QwtPlot::zoomAxis() with the given factor and cursor position, then replotAll(). Auto-replot is temporarily disabled to avoid redundant repaints.

Override this method to customize zoom behavior, e.g. zoom centered on the axis midpoint instead of the cursor position.

Parameters

[in]	factor	Zoom factor (>1 zoom in, <1 zoom out)
[in]	cursorPos	Cursor position in canvas coordinates

zoomFactor()

double QwtPlotAxisWheelInteraction::zoomFactor

(

)

const

Return the zoom factor.

Returns

Zoom factor

See also

setZoomFactor()

zoomModifiers()

Qt::KeyboardModifiers QwtPlotAxisWheelInteraction::zoomModifiers

(

)

const

Return the zoom modifiers.

Returns

Keyboard modifiers for zoom mode

See also

setZoomModifiers()

---

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

• /home/runner/work/QWT/QWT/src/plot/qwt_plot_axis_wheel_interaction.h
• /home/runner/work/QWT/QWT/src/plot/qwt_plot_axis_wheel_interaction.cpp