---
name: "QwtKnob"
section: "3"
platform: "linux"
package: "libqwt-doc"
version: "6.1.4-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/QwtKnob"
---

# QwtKnob(3)

The Knob Widget.

## NAME

QwtKnob - The Knob Widget.

## SYNOPSIS

`#include <qwt_knob.h>`

Inherits **QwtAbstractSlider**.

### Public Types

enum **KnobStyle** { **Flat**, **Raised**, **Sunken**, **Styled** }\
 Style of the knob surface.  enum **MarkerStyle** { **NoMarker** = -1, **Tick**, **Triangle**, **Dot**, **Nub**, **Notch** }\
 Marker type.

### Public Member Functions

**QwtKnob** (QWidget \*parent=NULL)\
 Constructor.  virtual **~QwtKnob** ()\
 Destructor.  void **setAlignment** (Qt::Alignment)\
 Set the alignment of the knob.  Qt::Alignment **alignment** () const\
 void **setKnobWidth** (int)\
 Change the knob's width.  int **knobWidth** () const\
 Return the width of the knob.  void **setNumTurns** (int)\
 Set the number of turns.  int **numTurns** () const\
 void **setTotalAngle** (double angle)\
 Set the total angle by which the knob can be turned.  double **totalAngle** () const\
 void **setKnobStyle** (**KnobStyle**)\
 Set the knob type.  **KnobStyle** **knobStyle** () const\
 void **setBorderWidth** (int)\
 Set the knob's border width.  int **borderWidth** () const\
 Return the border width.  void **setMarkerStyle** (**MarkerStyle**)\
 Set the marker type of the knob.  **MarkerStyle** **markerStyle** () const\
 void **setMarkerSize** (int)\
 Set the size of the marker.  int **markerSize** () const\
 virtual QSize **sizeHint** () const\
 virtual QSize **minimumSizeHint** () const\
 void **setScaleDraw** (**QwtRoundScaleDraw** \*)\
 const **QwtRoundScaleDraw** \* **scaleDraw** () const\
 **QwtRoundScaleDraw** \* **scaleDraw** ()\
 QRect **knobRect** () const\

### Protected Member Functions

virtual void **paintEvent** (QPaintEvent \*)\
 virtual void **changeEvent** (QEvent \*)\
 virtual void **drawKnob** (QPainter \*, const QRectF &) const\
 Draw the knob.  virtual void **drawFocusIndicator** (QPainter \*) const\
 virtual void **drawMarker** (QPainter \*, const QRectF &, double angle) const\
 Draw the marker at the knob's front.  virtual double **scrolledTo** (const QPoint &) const\
 Determine the value for a new position of the mouse.  virtual bool **isScrollPosition** (const QPoint &) const\
 Determine what to do when the user presses a mouse button.

### Additional Inherited Members

## Detailed Description

The Knob Widget.

The **QwtKnob** widget imitates look and behavior of a volume knob on a radio. It looks similar to QDial - not to **QwtDial**.

The value range of a knob might be divided into several turns.

The layout of the knob depends on the **knobWidth()**.

- •

  width \> 0 The diameter of the knob is fixed and the knob is aligned according to the **alignment()** flags inside of the contentsRect().

- •

  width \<= 0 The knob is extended to the minimum of width/height of the contentsRect() and aligned in the other direction according to **alignment()**.

Setting a fixed **knobWidth()** is helpful to align several knobs with different scale labels.

## 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**

- *Flat*

  *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*

- *Styled*

  *Build a radial gradient from QPalette::Button like it is used for QDial in various Qt styles.*

### 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.*

- *Triangle*

  *Paint a triangle 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*

## Constructor & Destructor Documentation

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

*Constructor. Construct a knob with an angle of 270°. The style is* **QwtKnob::Raised** *and the marker style is* **QwtKnob::Notch***. The width of the knob is set to 50 pixels.*

**Parameters:**

*parent Parent widget*

**See also:**

**setTotalAngle()**

## Member Function Documentation

### Qt::Alignment QwtKnob::alignment () const

**Returns:**

*Alignment of the knob inside of contentsRect()*

**See also:**

**setAlignment()***,* **knobWidth()***,* **knobRect()**

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

*Handle QEvent::StyleChange and QEvent::FontChange;*

**Parameters:**

*event Change event*

### void QwtKnob::drawFocusIndicator (QPainter \* painter) const` [protected]`, ` [virtual]`

*Draw the focus indicator*

**Parameters:**

*painter Painter*

### 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 ( clockwise, 0 at the 12 o'clock position )*

### bool QwtKnob::isScrollPosition (const QPoint & pos) const` [protected]`, ` [virtual]`

*Determine what to do when the user presses a mouse button.*

**Parameters:**

*pos Mouse position*

**Return values:**

*True,when pos is inside the circle of the knob.*

**See also:**

**scrolledTo()**

*Implements* **QwtAbstractSlider***.*

### QRect QwtKnob::knobRect () const

*Calculate the bounding rectangle of the knob without the scale*

**Returns:**

*Bounding rectangle of the knob*

**See also:**

**knobWidth()***,* **alignment()***, QWidget::contentsRect()*

### QwtKnob::KnobStyle QwtKnob::knobStyle () const

**Returns:**

*Marker type of the knob*

**See also:**

**setKnobStyle()***,* **setBorderWidth()**

### int QwtKnob::markerSize () const

**Returns:**

*Marker size*

**See also:**

**setMarkerSize()**

### QwtKnob::MarkerStyle QwtKnob::markerStyle () const

**Returns:**

*Marker type of the knob*

**See also:**

**setMarkerStyle()***,* **setMarkerSize()**

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

**Returns:**

*Minimum size hint*

**See also:**

**sizeHint()**

### int QwtKnob::numTurns () const

**Returns:**

*Number of turns.*

*When the total angle is below 360°* **numTurns()** *is ceiled to 1.*

**See also:**

**setNumTurns()***,* **setTotalAngle()***,* **totalAngle()**

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

*Repaint the knob*

**Parameters:**

*event Paint event*

### const QwtRoundScaleDraw \* QwtKnob::scaleDraw () const

**Returns:**

*the scale draw of the knob*

**See also:**

**setScaleDraw()**

### QwtRoundScaleDraw \* QwtKnob::scaleDraw ()

**Returns:**

*the scale draw of the knob*

**See also:**

**setScaleDraw()**

### double QwtKnob::scrolledTo (const QPoint & pos) const` [protected]`, ` [virtual]`

*Determine the value for a new position of the mouse.*

**Parameters:**

*pos Mouse position*

**Returns:**

*Value for the mouse position*

**See also:**

**isScrollPosition()**

*Implements* **QwtAbstractSlider***.*

### void QwtKnob::setAlignment (Qt::Alignment alignment)

*Set the alignment of the knob. Similar to a QLabel::alignment() the flags decide how to align the knob inside of contentsRect().*

*The default setting is Qt::AlignCenter*

**Parameters:**

*alignment Or'd alignment flags*

**See also:**

**alignment()***,* **setKnobWidth()***,* **knobRect()**

### 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. Setting a fixed value for the diameter of the knob is helpful for aligning several knobs in a row.*

**Parameters:**

*width New width*

**See also:**

**knobWidth()***,* **setAlignment()**

**Note:**

*Modifies the sizePolicy()*

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

*Set the size of the marker. When setting a size \<= 0 the marker will automatically scaled to 40% of the radius of the knob.*

**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 QwtKnob::setNumTurns (int numTurns)

*Set the number of turns. When numTurns \> 1 the knob can be turned several times around its axis*

- •

  *otherwise the total angle is floored to 360°.*

**See also:**

**numTurns()***,* **totalAngle()***,* **setTotalAngle()**

### 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 QwtKnob::setTotalAngle (double angle)

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

**Parameters:**

*angle Angle in degrees.*

*The angle has to be between \[10, 360\] degrees. Angles above 360 ( so that the knob can be turned several times around its axis ) have to be set using* **setNumTurns()***.*

*The default angle is 270 degrees.*

**See also:**

**totalAngle()***,* **setNumTurns()**

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

**Returns:**

**sizeHint()**

### double QwtKnob::totalAngle () const

**Returns:**

*the total angle*

**See also:**

**setTotalAngle()***,* **setNumTurns()***,* **numTurns()**

## Author

*Generated automatically by Doxygen for Qwt User's Guide from the source code.*