Qwt User's Guide
QwtKnob Class Reference

The Knob Widget. More...

#include <qwt_knob.h>

Inheritance diagram for QwtKnob:

Public Types

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

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 bw)
 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 QwtRoundScaleDrawscaleDraw () const
QwtRoundScaleDrawscaleDraw ()
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 arc) 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.

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.

knob.png

Member Enumeration Documentation

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.

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:
parentParent 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:
eventChange event
void QwtKnob::drawFocusIndicator ( QPainter *  painter) const [protected, virtual]

Draw the focus indicator

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

Draw the knob.

Parameters:
painterpainter
knobRectBounding 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:
painterPainter
rectBounding rectangle of the knob without scale
angleAngle 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:
posMouse position
Return values:
True,whenpos 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()
Returns:
Marker type of the knob
See also:
setKnobStyle(), setBorderWidth()
int QwtKnob::markerSize ( ) const
Returns:
Marker size
See also:
setMarkerSize()
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:
eventPaint event
Returns:
the scale draw of the knob
See also:
setScaleDraw()
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:
posMouse 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:
alignmentOr'd alignment flags
See also:
alignment(), setKnobWidth(), knobRect()
void QwtKnob::setBorderWidth ( int  borderWidth)

Set the knob's border width.

Parameters:
borderWidthnew border width
void QwtKnob::setKnobStyle ( KnobStyle  knobStyle)

Set the knob type.

Parameters:
knobStyleKnob 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:
widthNew 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:
markerStyleMarker 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()

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:
angleAngle 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()

List of all members.

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