# QwtKnob Class Reference

The Knob Widget. More...

`#include <qwt_knob.h>`

Inheritance diagram for QwtKnob:
[legend]

List of all members.

## Public Types

enum | KnobStyle { NoStyle = -1, Raised, Sunken }
enum | MarkerStyle { NoMarker = -1, Tick, Dot, Nub, Notch }
enum | ScrollMode { ScrNone, ScrMouse, ScrTimer, ScrDirect, ScrPage }

## Public Slots

virtual void | fitValue (double val)
virtual void | incValue (int steps)
virtual void | setReadOnly (bool)
virtual void | setValue (double val)

## Signals

void | sliderMoved (double value)
void | sliderPressed ()
void | sliderReleased ()
void | valueChanged (double value)

## Public Member Functions

bool | autoScale () const
int | borderWidth () const
virtual void | incPages (int)
bool | isReadOnly () const
bool | isValid () const
KnobStyle | knobStyle () const
int | knobWidth () const
int | markerSize () const
MarkerStyle | markerStyle () const
virtual double | mass () const
double | maxValue () const
virtual QSize | minimumSizeHint () const
double | minValue () const
Qt::Orientation | orientation () const
int | pageSize () const
bool | periodic () const
| QwtKnob (QWidget *parent=NULL)
const QwtRoundScaleDraw * | scaleDraw () const
QwtRoundScaleDraw * | scaleDraw ()
const QwtScaleEngine * | scaleEngine () const
QwtScaleEngine * | scaleEngine ()
const QwtScaleMap & | scaleMap () const
int | scaleMaxMajor () const
int | scaleMaxMinor () const
void | setAutoScale ()
void | setBorderWidth (int bw)
void | setKnobStyle (KnobStyle)
void | setKnobWidth (int w)
void | setMarkerSize (int)
void | setMarkerStyle (MarkerStyle)
virtual void | setMass (double val)
virtual void | setOrientation (Qt::Orientation o)
void | setPeriodic (bool tf)
void | setRange (double vmin, double vmax, double vstep=0.0, int pagesize=1)
void | setScale (const QwtScaleDiv &)
void | setScale (const QwtInterval &, double step=0.0)
void | setScale (double vmin, double vmax, double step=0.0)
void | setScaleDraw (QwtRoundScaleDraw *)
void | setScaleEngine (QwtScaleEngine *)
void | setScaleMaxMajor (int ticks)
void | setScaleMaxMinor (int ticks)
void | setStep (double)
void | setTotalAngle (double angle)
void | setTracking (bool enable)
void | setUpdateTime (int t)
void | setValid (bool valid)
virtual QSize | sizeHint () const
double | step () const
void | stopMoving ()
double | totalAngle () const
double | value () const
virtual | ~QwtKnob ()

## Protected Member Functions

const QwtAbstractScaleDraw * | abstractScaleDraw () const
QwtAbstractScaleDraw * | abstractScaleDraw ()
virtual void | changeEvent (QEvent *)
virtual void | drawKnob (QPainter *, const QRectF &) const
virtual void | drawMarker (QPainter *, const QRectF &, double arc) const
double | exactPrevValue () const
double | exactValue () const
virtual void | getScrollMode (const QPoint &, QwtAbstractSlider::ScrollMode &, int &direction) const
virtual double | getValue (const QPoint &p)
virtual void | keyPressEvent (QKeyEvent *e)
virtual void | mouseMoveEvent (QMouseEvent *e)
double | mouseOffset () const
virtual void | mousePressEvent (QMouseEvent *e)
virtual void | mouseReleaseEvent (QMouseEvent *e)
virtual void | paintEvent (QPaintEvent *)
double | prevValue () const
void | rescale (double vmin, double vmax, double step=0.0)
virtual void | resizeEvent (QResizeEvent *)
int | scrollMode () const
void | setAbstractScaleDraw (QwtAbstractScaleDraw *)
void | setMouseOffset (double)
virtual void | setPosition (const QPoint &)
virtual void | stepChange ()
virtual void | timerEvent (QTimerEvent *e)
virtual void | wheelEvent (QWheelEvent *e)

## Detailed Description

The Knob Widget.

The QwtKnob widget imitates look and behaviour of a volume knob on a radio. It contains a scale around the knob which is set up automatically or can be configured manually (see QwtAbstractScale). Automatic scrolling is enabled when the user presses a mouse button on the scale. For a description of signals, slots and other members, see QwtAbstractSlider.

See also:
  QwtAbstractSlider and QwtAbstractScale for the descriptions of the inherited members.

## Member Enumeration Documentation

enum QwtKnob::KnobStyle

Style of the knob surface.

Depending on the KnobStyle the surface of the knob is filled from the brushes of the widget palette().

See also:
  setKnobStyle(), knobStyle()

Enumerator:

  NoStyle | Fill the knob with a brush from QPalette::Button.
  Raised | Build a gradient from QPalette::Midlight and QPalette::Button.
  Sunken | Build a gradient from QPalette::Midlight, QPalette::Button and QPalette::Midlight

enum QwtKnob::MarkerStyle

Marker type.

The marker indicates the current value on the knob The default setting is a Notch marker.

See also:
  setMarkerStyle(), setMarkerSize()

Enumerator:

  NoMarker | Don't paint any marker.
  Tick | Paint a single tick in QPalette::ButtonText color.
  Dot | Paint a circle in QPalette::ButtonText color.
  Nub | Draw a raised ellipse with a gradient build from QPalette::Light and QPalette::Mid
  Notch | Draw a sunken ellipse with a gradient build from QPalette::Light and QPalette::Mid

enum QwtAbstractSlider::ScrollMode`[inherited]`

Scroll mode

See also:
  getScrollMode()

Enumerator:

  ScrNone | Scrolling switched off. Don't change the value.
  ScrMouse | Change the value while the user keeps the button pressed and moves the mouse.
  ScrTimer | Automatic scrolling. Increment the value in the specified direction as long as the user keeps the button pressed.
  ScrPage | Automatic scrolling. Same as ScrTimer, but increment by page size.

## Constructor & Destructor Documentation

QwtKnob::QwtKnob | ( | QWidget * | parent = `NULL` | ) | `[explicit]`

Constructor

Parameters:

  parent | Parent widget

QwtKnob::~QwtKnob | ( |  | ) | `[virtual]`

Destructor.

## Member Function Documentation

const QwtAbstractScaleDraw * QwtAbstractScale::abstractScaleDraw | ( |  | ) | const`[protected, inherited]`

Returns:
  Scale draw

See also:
  setAbstractScaleDraw()

QwtAbstractScaleDraw * QwtAbstractScale::abstractScaleDraw | ( |  | ) | `[protected, inherited]`

Returns:
  Scale draw

See also:
  setAbstractScaleDraw()

bool QwtAbstractScale::autoScale | ( |  | ) | const`[inherited]`

Returns:
  `true` if autoscaling is enabled

int QwtKnob::borderWidth | ( |  | ) | const

Return the border width.

void QwtKnob::changeEvent | ( | QEvent * | event | ) | `[protected, virtual]`

Handle QEvent::StyleChange and QEvent::FontChange;

Parameters:

  event | Change event

void QwtKnob::drawKnob | ( | QPainter * | painter,
|  | const QRectF & | knobRect
| ) |  | const`[protected, virtual]`

Draw the knob.

Parameters:

  painter | painter
  knobRect | Bounding rectangle of the knob (without scale)

void QwtKnob::drawMarker | ( | QPainter * | painter,
|  | const QRectF & | rect,
|  | double | angle
| ) |  | const`[protected, virtual]`

Draw the marker at the knob's front.

Parameters:

  painter | Painter
  rect | Bounding rectangle of the knob without scale
  angle | Angle of the marker in degrees

double QwtDoubleRange::exactPrevValue | ( |  | ) | const`[protected, inherited]`

Returns the exact previous value.

double QwtDoubleRange::exactValue | ( |  | ) | const`[protected, inherited]`

Returns the exact value.

The exact value is the value which QwtDoubleRange::value would return if the value were not adjusted to the step raster. It differs from the current value only if fitValue() or incValue() have been used before. This function is intended for internal use in derived classes.

void QwtAbstractSlider::fitValue | ( | double | value | ) | `[virtual, slot, inherited]`

Set the slider's value to the nearest integer multiple of the step size.

Parameters:

  value | Value

See also:
  setValue(), incValue()

Reimplemented from QwtDoubleRange.

void QwtKnob::getScrollMode | ( | const QPoint & | pos,
|  | QwtAbstractSlider::ScrollMode & | scrollMode,
|  | int & | direction
| ) |  | const`[protected, virtual]`

Set the scrolling mode and direction.

Called by QwtAbstractSlider

Parameters:

  pos | Point in question
  scrollMode | Scrolling mode
  direction | Direction

Implements QwtAbstractSlider.

double QwtKnob::getValue | ( | const QPoint & | pos | ) | `[protected, virtual]`

Determine the value corresponding to a specified position.

Called by QwtAbstractSlider

Parameters:

  pos | point

Implements QwtAbstractSlider.

void QwtDoubleRange::incPages | ( | int | nPages | ) | `[virtual, inherited]`

Increment the value by a specified number of pages.

Parameters:

  nPages | Number of pages to increment. A negative number decrements the value.

Warning:
  The Page size is specified in the constructor.

void QwtAbstractSlider::incValue | ( | int | steps | ) | `[virtual, slot, inherited]`

Increment the value by a specified number of steps.

Parameters:

  steps | number of steps

See also:
  setValue()

Reimplemented from QwtDoubleRange.

bool QwtAbstractSlider::isReadOnly | ( |  | ) | const`[inherited]`

In read only mode the slider can't be controlled by mouse or keyboard.

Returns:
  true if read only

See also:
  setReadOnly()

bool QwtAbstractSlider::isValid | ( |  | ) | const`[inline, inherited]`

See also:
  QwtDblRange::isValid()

Reimplemented from QwtDoubleRange.

void QwtAbstractSlider::keyPressEvent | ( | QKeyEvent * | e | ) | `[protected, virtual, inherited]`

Handles key events

- Key_Down, KeyLeft
  Decrement by 1
- Key_Up, Key_Right
  Increment by 1

Parameters:

  e | Key event

See also:
  isReadOnly()

Reimplemented in QwtCompass, and QwtDial.

QwtKnob::KnobStyle QwtKnob::knobStyle | ( |  | ) | const

Returns:
  Marker type of the knob

See also:
  setKnobStyle(), setBorderWidth()

int QwtKnob::knobWidth | ( |  | ) | const

Return the width of the knob.

int QwtKnob::markerSize | ( |  | ) | const

Return the marker size.

QwtKnob::MarkerStyle QwtKnob::markerStyle | ( |  | ) | const

Returns:
  Marker type of the knob

See also:
  setMarkerStyle(), setMarkerSize()

double QwtAbstractSlider::mass | ( |  | ) | const`[virtual, inherited]`

Returns:
  mass

See also:
  setMass()

Reimplemented in QwtWheel.

double QwtDoubleRange::maxValue | ( |  | ) | const`[inherited]`

Returns the value of the second border of the range.

maxValue returns the value which has been specified as the second parameter in QwtDoubleRange::setRange.

See also:
  setRange()

Reimplemented in QwtCounter.

QSize QwtKnob::minimumSizeHint | ( |  | ) | const`[virtual]`

Return a minimum size hint.

Warning:
  The return value of QwtKnob::minimumSizeHint() depends on the font and the scale.

double QwtDoubleRange::minValue | ( |  | ) | const`[inherited]`

Returns the value at the first border of the range.

minValue returns the value which has been specified as the first parameter in setRange().

See also:
  setRange()

Reimplemented in QwtCounter.

void QwtAbstractSlider::mouseMoveEvent | ( | QMouseEvent * | e | ) | `[protected, virtual, inherited]`

Mouse Move Event handler

Parameters:

  e | Mouse event

double QwtAbstractSlider::mouseOffset | ( |  | ) | const`[protected, inherited]`

See also:
  setMouseOffset()

void QwtAbstractSlider::mousePressEvent | ( | QMouseEvent * | e | ) | `[protected, virtual, inherited]`

Mouse press event handler

Parameters:

  e | Mouse event

void QwtAbstractSlider::mouseReleaseEvent | ( | QMouseEvent * | e | ) | `[protected, virtual, inherited]`

Mouse Release Event handler

Parameters:

  e | Mouse event

Qt::Orientation QwtAbstractSlider::orientation | ( |  | ) | const`[inherited]`

Returns:
  Orientation

See also:
  setOrientation()

int QwtDoubleRange::pageSize | ( |  | ) | const`[inherited]`

Returns the page size in steps.

void QwtKnob::paintEvent | ( | QPaintEvent * | event | ) | `[protected, virtual]`

Repaint the knob

Parameters:

  event | Paint event

bool QwtDoubleRange::periodic | ( |  | ) | const`[inherited]`

Returns true if the range is periodic.

See also:
  setPeriodic()

double QwtDoubleRange::prevValue | ( |  | ) | const`[protected, inherited]`

Returns the previous value.

void QwtAbstractScale::rescale | ( | double | vmin,
|  | double | vmax,
|  | double | stepSize = `0.0`
| ) |  | `[protected, inherited]`

Recalculate the scale division and update the scale draw.

Parameters:

  vmin | Lower limit of the scale interval
  vmax | Upper limit of the scale interval
  stepSize | Major step size

See also:
  scaleChange()

void QwtKnob::resizeEvent | ( | QResizeEvent * | event | ) | `[protected, virtual]`

Qt Resize Event

Parameters:

  event | Resize event

QwtRoundScaleDraw * QwtKnob::scaleDraw | ( |  | ) |

Returns:
  the scale draw of the knob

See also:
  setScaleDraw()

const QwtRoundScaleDraw * QwtKnob::scaleDraw | ( |  | ) | const

Returns:
  the scale draw of the knob

See also:
  setScaleDraw()

const QwtScaleEngine * QwtAbstractScale::scaleEngine | ( |  | ) | const`[inherited]`

Returns:
  Scale engine

See also:
  setScaleEngine()

QwtScaleEngine * QwtAbstractScale::scaleEngine | ( |  | ) | `[inherited]`

Returns:
  Scale engine

See also:
  setScaleEngine()

const QwtScaleMap & QwtAbstractScale::scaleMap | ( |  | ) | const`[inherited]`

Returns:
  abstractScaleDraw()->scaleMap()

int QwtAbstractScale::scaleMaxMajor | ( |  | ) | const`[inherited]`

Returns:
  Max. number of major tick intervals The default value is 5.

int QwtAbstractScale::scaleMaxMinor | ( |  | ) | const`[inherited]`

Returns:
  Max. number of minor tick intervals The default value is 3.

int QwtAbstractSlider::scrollMode | ( |  | ) | const`[protected, inherited]`

sa ScrollMode

void QwtAbstractScale::setAbstractScaleDraw | ( | QwtAbstractScaleDraw * | scaleDraw | ) | `[protected, inherited]`

Set a scale draw.

scaleDraw has to be created with new and will be deleted in ~QwtAbstractScale or the next call of setAbstractScaleDraw.

void QwtAbstractScale::setAutoScale | ( |  | ) | `[inherited]`

Advise the widget to control the scale range internally.

Autoscaling is on by default.

See also:
  setScale(), autoScale()

void QwtKnob::setBorderWidth | ( | int | borderWidth | ) |

Set the knob's border width.

Parameters:

  borderWidth | new border width

void QwtKnob::setKnobStyle | ( | KnobStyle | knobStyle | ) |

Set the knob type.

Parameters:

  knobStyle | Knob type

See also:
  knobStyle(), setBorderWidth()

void QwtKnob::setKnobWidth | ( | int | width | ) |

Change the knob's width.

The specified width must be >= 5, or it will be clipped.

Parameters:

  width | New width

void QwtKnob::setMarkerSize | ( | int | size | ) |

Set the size of the marker.

See also:
  markerSize(), markerStyle()

void QwtKnob::setMarkerStyle | ( | MarkerStyle | markerStyle | ) |

Set the marker type of the knob.

Parameters:

  markerStyle | Marker type

See also:
  markerStyle(), setMarkerSize()

void QwtAbstractSlider::setMass | ( | double | val | ) | `[virtual, inherited]`

Set the slider's mass for flywheel effect.

If the slider's mass is greater then 0, it will continue to move after the mouse button has been released. Its speed decreases with time at a rate depending on the slider's mass. A large mass means that it will continue to move for a long time.

Derived widgets may overload this function to make it public.

Parameters:

  val | New mass in kg

See also:
  mass()

Reimplemented in QwtWheel.

void QwtAbstractSlider::setMouseOffset | ( | double | offset | ) | `[protected, inherited]`

See also:
  mouseOffset()

void QwtAbstractSlider::setOrientation | ( | Qt::Orientation | o | ) | `[virtual, inherited]`

Set the orientation.

Parameters:

  o | Orientation. Allowed values are Qt::Horizontal and Qt::Vertical.

Reimplemented in QwtSlider, and QwtWheel.

void QwtDoubleRange::setPeriodic | ( | bool | tf | ) | `[inherited]`

Make the range periodic.

When the range is periodic, the value will be set to a point inside the interval such that

    point = value + n * width

if the user tries to set a new value which is outside the range. If the range is nonperiodic (the default), values outside the range will be clipped.

Parameters:

  tf | true for a periodic range

void QwtAbstractSlider::setPosition | ( | const QPoint & | p | ) | `[protected, virtual, inherited]`

Move the slider to a specified point, adjust the value and emit signals if necessary.

void QwtDoubleRange::setRange | ( | double | vmin,
|  | double | vmax,
|  | double | vstep = `0.0`,
|  | int | pageSize = `1`
| ) |  | `[inherited]`

Specify range and step size.

Parameters:

  vmin | lower boundary of the interval
  vmax | higher boundary of the interval
  vstep | step width
  pageSize | page size in steps

Warning:
  - A change of the range changes the value if it lies outside the new range. The current value will *not* be adjusted to the new step raster.
  - vmax < vmin is allowed.
  - If the step size is left out or set to zero, it will be set to 1/100 of the interval length.
  - If the step size has an absurd value, it will be corrected to a better one.

void QwtAbstractSlider::setReadOnly | ( | bool | readOnly | ) | `[virtual, slot, inherited]`

En/Disable read only mode

In read only mode the slider can't be controlled by mouse or keyboard.

Parameters:

  readOnly | Enables in case of true

See also:
  isReadOnly()

void QwtAbstractScale::setScale | ( | double | vmin,
|  | double | vmax,
|  | double | stepSize = `0.0`
| ) |  | `[inherited]`

Specify a scale.

Disable autoscaling and define a scale by an interval and a step size

Parameters:

  vmin | lower limit of the scale interval
  vmax | upper limit of the scale interval
  stepSize | major step size

See also:
  setAutoScale()

void QwtAbstractScale::setScale | ( | const QwtInterval & | interval,
|  | double | stepSize = `0.0`
| ) |  | `[inherited]`

Specify a scale.

Disable autoscaling and define a scale by an interval and a step size

Parameters:

  interval | Interval
  stepSize | major step size

See also:
  setAutoScale()

void QwtAbstractScale::setScale | ( | const QwtScaleDiv & | scaleDiv | ) | `[inherited]`

Specify a scale.

Disable autoscaling and define a scale by a scale division

Parameters:

  scaleDiv | Scale division

See also:
  setAutoScale()

void QwtKnob::setScaleDraw | ( | QwtRoundScaleDraw * | scaleDraw | ) |

Change the scale draw of the knob

For changing the labels of the scales, it is necessary to derive from QwtRoundScaleDraw and overload QwtRoundScaleDraw::label().

See also:
  scaleDraw()

void QwtAbstractScale::setScaleEngine | ( | QwtScaleEngine * | scaleEngine | ) | `[inherited]`

Set a scale engine.

The scale engine is responsible for calculating the scale division, and in case of auto scaling how to align the scale.

scaleEngine has to be created with new and will be deleted in ~QwtAbstractScale or the next call of setScaleEngine.

void QwtAbstractScale::setScaleMaxMajor | ( | int | ticks | ) | `[inherited]`

Set the maximum number of major tick intervals.

The scale's major ticks are calculated automatically such that the number of major intervals does not exceed ticks. The default value is 5.

Parameters:

  ticks | maximal number of major ticks.

See also:
  QwtAbstractScaleDraw

void QwtAbstractScale::setScaleMaxMinor | ( | int | ticks | ) | `[inherited]`

Set the maximum number of minor tick intervals.

The scale's minor ticks are calculated automatically such that the number of minor intervals does not exceed ticks. The default value is 3.

Parameters:

  ticks |

See also:
  QwtAbstractScaleDraw

void QwtDoubleRange::setStep | ( | double | vstep | ) | `[inherited]`

Change the step raster.

Parameters:

  vstep | new step width

Warning:
  The value will not be adjusted to the new step raster.

Reimplemented in QwtCounter.

void QwtKnob::setTotalAngle | ( | double | angle | ) |

Set the total angle by which the knob can be turned.

Parameters:

  angle | Angle in degrees.

The default angle is 270 degrees. It is possible to specify an angle of more than 360 degrees so that the knob can be turned several times around its axis.

void QwtAbstractSlider::setTracking | ( | bool | enable | ) | `[inherited]`

Enables or disables tracking.

If tracking is enabled, the slider emits a valueChanged() signal whenever its value changes (the default behaviour). If tracking is disabled, the value changed() signal will only be emitted if:

- the user releases the mouse button and the value has changed or
- at the end of automatic scrolling.

Tracking is enabled by default.

Parameters:

  enable | `true` (enable) or `false` (disable) tracking.

void QwtAbstractSlider::setUpdateTime | ( | int | t | ) | `[inherited]`

Specify the update interval for automatic scrolling.

Parameters:

  t | update interval in milliseconds

See also:
  getScrollMode()

void QwtAbstractSlider::setValid | ( | bool | valid | ) | `[inline, inherited]`

Parameters:

  valid | true/false

See also:
  QwtDblRange::isValid()

Reimplemented from QwtDoubleRange.

void QwtAbstractSlider::setValue | ( | double | val | ) | `[virtual, slot, inherited]`

Move the slider to a specified value.

This function can be used to move the slider to a value which is not an integer multiple of the step size.

Parameters:

  val | new value

See also:
  fitValue()

Reimplemented from QwtDoubleRange.

QSize QwtKnob::sizeHint | ( |  | ) | const`[virtual]`

Returns:
  minimumSizeHint()

void QwtAbstractSlider::sliderMoved | ( | double | value | ) | `[signal, inherited]`

This signal is emitted when the user moves the slider with the mouse.

Parameters:

  value | new value

void QwtAbstractSlider::sliderPressed | ( |  | ) | `[signal, inherited]`

This signal is emitted when the user presses the movable part of the slider (start ScrMouse Mode).

void QwtAbstractSlider::sliderReleased | ( |  | ) | `[signal, inherited]`

This signal is emitted when the user releases the movable part of the slider.

double QwtDoubleRange::step | ( |  | ) | const`[inherited]`

Returns:
  the step size

See also:
  setStep(), setRange()

Reimplemented in QwtCounter.

void QwtDoubleRange::stepChange | ( |  | ) | `[protected, virtual, inherited]`

Notify a change of the step size.

This virtual function is called whenever the step size changes. The default implementation does nothing.

void QwtAbstractSlider::stopMoving | ( |  | ) | `[inherited]`

Stop updating if automatic scrolling is active.

void QwtAbstractSlider::timerEvent | ( | QTimerEvent * | e | ) | `[protected, virtual, inherited]`

Qt timer event

Parameters:

  e | Timer event

double QwtKnob::totalAngle | ( |  | ) | const

Return the total angle.

double QwtDoubleRange::value | ( |  | ) | const`[inherited]`

Returns the current value.

Reimplemented in QwtCounter.

void QwtAbstractSlider::valueChanged | ( | double | value | ) | `[signal, inherited]`

Notify a change of value.

In the default setting (tracking enabled), this signal will be emitted every time the value changes ( see setTracking() ).

Parameters:

  value | new value

void QwtAbstractSlider::wheelEvent | ( | QWheelEvent * | e | ) | `[protected, virtual, inherited]`

Wheel Event handler

Parameters:

  e | Whell event