Qwt provides a series of instrument widget components for numeric display and interactive control. These widgets are suitable for instrument panels, control systems, data monitoring, and similar scenarios.
| Widget Class |
Description |
QwtDial |
Dial/gauge |
QwtKnob |
Knob control |
QwtSlider |
Slider control |
QwtThermo |
Thermometer/progress bar |
QwtWheel |
Wheel control |
QwtCounter |
Numeric counter |
QwtCompass |
Compass |
Usage
The widget demo is located at: examples/2D/controls. Screenshots:
1. QwtDial - Dial
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22 | #include <QwtDial>
QwtDial* dial = new QwtDial();
// Set range
dial->setRange(0.0, 360.0); // 0-360 degrees
// Set current value
dial->setValue(90.0);
// Set scale step
dial->setScaleStep(30.0); // One tick every 30 degrees
// Set scale position
dial->setScalePosition(QwtDial::Inside); // Ticks on inside
// Other options: Outside (outside), NoScale (no scale)
// Set needle style
dial->setNeedle(new QwtDialSimpleNeedle(QwtDialSimpleNeedle::Arrow));
// Connect value change signal
connect(dial, SIGNAL(valueChanged(double)), this, SLOT(onValueChanged(double)));
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2. QwtKnob - Knob Control
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22 | #include <QwtKnob>
QwtKnob* knob = new QwtKnob();
// Set range
knob->setRange(0, 100);
// Set current value
knob->setValue(50);
// Set scale style
knob->setScalePosition(QwtKnob::OutsideScale);
// Set knob appearance
knob->setKnobStyle(QwtKnob::RaisedStyle); // Raised style
// Other options: FlatStyle (flat), SunkenStyle (sunken)
// Set knob width
knob->setKnobWidth(50);
// Set mouse tracking mode
knob->setTracking(true); // Update value in real-time while dragging
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3. QwtSlider - Slider Control
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24 | #include <QwtSlider>
QwtSlider* slider = new QwtSlider();
// Set range
slider->setRange(0.0, 100.0);
// Set current value
slider->setValue(30.0);
// Set orientation
slider->setOrientation(Qt::Horizontal); // Horizontal slider
// or Qt::Vertical (vertical slider)
// Set scale position
slider->setScalePosition(QwtSlider::TrailingScale); // Scale on trailing side
// Other options: LeadingScale, NoScale
// Set slider handle style
slider->setHandleSize(QSize(10, 20)); // Slider handle size
// Set step values
slider->setSingleStep(1.0);
slider->setPageStep(10.0);
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4. QwtThermo - Thermometer
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25 | #include <QwtThermo>
QwtThermo* thermo = new QwtThermo();
// Set range
thermo->setRange(0.0, 100.0);
// Set current value
thermo->setValue(75.0);
// Set orientation
thermo->setOrientation(Qt::Vertical);
// Set fill color
thermo->setFillBrush(QBrush(Qt::red));
// Set pipe width
thermo->setPipeWidth(10);
// Set scale position
thermo->setScalePosition(QwtThermo::TrailingScale);
// Set alarm level
thermo->setAlarmLevel(80.0); // Alarm at 80 degrees
thermo->setAlarmBrush(QBrush(Qt::darkRed));
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5. QwtWheel - Wheel Control
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25 | #include <QwtWheel>
QwtWheel* wheel = new QwtWheel();
// Set range
wheel->setRange(0, 360);
// Set current value
wheel->setValue(180);
// Set orientation
wheel->setOrientation(Qt::Horizontal);
// Set wheel width
wheel->setWheelWidth(30);
// Set border width
wheel->setBorderWidth(2);
// Set step values
wheel->setSingleStep(1);
wheel->setPageStep(15);
// Set mouse tracking
wheel->setTracking(true);
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6. QwtCounter - Numeric Counter
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19 | #include <QwtCounter>
QwtCounter* counter = new QwtCounter();
// Set range
counter->setRange(0, 9999);
// Set current value
counter->setValue(100);
// Set step buttons
counter->setNumButtons(3); // 3 step buttons
// Set step values
counter->setSingleStep(1);
counter->setPageStep(100);
// Set wrap mode
counter->setWrap(true); // Wrap around at boundaries
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7. QwtCompass - Compass
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20 | #include <QwtCompass>
QwtCompass* compass = new QwtCompass();
// Set range (angle)
compass->setRange(0.0, 360.0);
// Set current direction
compass->setValue(45.0); // 45 degrees north-east
// Set rose style
compass->setRose(new QwtSimpleCompassRose());
// Set scale labels
compass->setLabelMap({
{0, "N"}, {90, "E"}, {180, "S"}, {270, "W"}
});
// Set needle
compass->setNeedle(new QwtCompassWindArrow());
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Core Common Methods
All widgets inherit from QwtAbstractSlider and share the following methods:
| Method |
Description |
setRange() |
Set numeric range |
setValue() |
Set current value |
value() |
Get current value |
setSingleStep() |
Set single step increment |
setPageStep() |
Set page step increment |
setTracking() |
Set mouse tracking |
setWrapping() |
Set wrap mode |
Widget Usage Recommendations
- Dials are suitable for angle or direction display
- Knobs are suitable for parameter adjustment
- Sliders are suitable for linear range adjustment
- Thermometers are suitable for progress or temperature display
- Wheels are suitable for continuous smooth adjustment
Related Examples
- Widget demo:
examples/2D/controls
- Compass:
examples/2D/dials
More screenshots of the widget demo:
