1.概述

QwtDial是Qwt库中的一个类，用于绘制一个可旋转的仪表盘。

以下是类继承关系：

2.常用方法

void setOrigin(double origin) 设置仪表盘的原点角度，以度为单位，默认为0度，正值为逆时针旋转，负值为顺时针旋转。

void setScaleArc (double minArc, double maxArc) 设置最小、最大角度

void setMinScaleArc (double) 设置刻度盘的最小角度

void setMaxScaleArc (double) 设置刻度盘的最大角度

void setValue(double value) 设置当前指示器的值。

void setNeedle(QwtDialSimpleNeedle *needle) 设置指针的样式，可以通过创建一个QwtDialNeedle指针对象并设置其样式来自定义指针。

void setScaleDraw (QwtRoundScaleDraw *) 设置绘制的坐标轴

void setScale (double lowerBound, double upperBound) 设置范围

void setScaleStepSize (double stepSize) 设置步长

3.示例

 

自定义SpeedoMeter类继承QwtDial。

#ifndef SPEEDOMETER_H
#define SPEEDOMETER_H

#include <QPainter>
#include "qwt_dial.h"
#include "qwt_round_scale_draw.h"
#include "qwt_dial_needle.h"

class SpeedoMeter : public QwtDial
{
public:
    SpeedoMeter( QWidget* parent = NULL );

    void setLabel( const QString& );
    QString label() const;

protected:
    virtual void drawScaleContents( QPainter* painter,
      const QPointF& center, double radius ) const QWT_OVERRIDE;

private:
    QString m_label;
};

#endif // SPEEDOMETER_H

#include "SpeedoMeter.h"
#include <QPainter>

SpeedoMeter::SpeedoMeter( QWidget* parent )
    : QwtDial( parent )
    , m_label( "km/h" )
{
    QwtRoundScaleDraw* scaleDraw = new QwtRoundScaleDraw();
    scaleDraw->setSpacing( 8 );
    scaleDraw->enableComponent( QwtAbstractScaleDraw::Backbone, false );
    scaleDraw->setTickLength( QwtScaleDiv::MinorTick, 0 );
    scaleDraw->setTickLength( QwtScaleDiv::MediumTick, 4 );
    scaleDraw->setTickLength( QwtScaleDiv::MajorTick, 8 );
    setScaleDraw( scaleDraw );

    setWrapping( false );
    setReadOnly( true );

    setOrigin( 135.0 );
    setScaleArc( 0.0, 270.0 );

    QwtDialSimpleNeedle* needle = new QwtDialSimpleNeedle(
        QwtDialSimpleNeedle::Arrow, true, Qt::red,
        QColor( Qt::gray ).lighter( 130 ) );
    setNeedle( needle );

    setScaleStepSize( 20.0 );
    setScale( 0.0, 240.0 );
    this->scaleDraw()->setPenWidthF( 2 );
}

void SpeedoMeter::setLabel( const QString& label )
{
    m_label = label;
    update();
}

QString SpeedoMeter::label() const
{
    return m_label;
}

void SpeedoMeter::drawScaleContents( QPainter* painter,
    const QPointF& center, double radius ) const
{
    QRectF rect( 0.0, 0.0, 2.0 * radius, 2.0 * radius - 10.0 );
    rect.moveCenter( center );

    const QColor color = palette().color( QPalette::Text );
    painter->setPen( color );

    const int flags = Qt::AlignBottom | Qt::AlignHCenter;
    painter->drawText( rect, flags, m_label );
}

使用：

#ifndef SPEEDOMETERWIDGET_H
#define SPEEDOMETERWIDGET_H

#include <QWidget>
#include <QTimerEvent>

namespace Ui {
class SpeedoMeterWidget;
}

class SpeedoMeterWidget : public QWidget
{
    Q_OBJECT

public:
    explicit SpeedoMeterWidget(QWidget *parent = 0);
    ~SpeedoMeterWidget();

    void changeSpeed();

protected:
    virtual void timerEvent( QTimerEvent* event );

private:
    Ui::SpeedoMeterWidget *ui;

    int m_timerId;
};

#endif // SPEEDOMETERWIDGET_H


#include "SpeedoMeterWidget.h"
#include "ui_SpeedoMeterWidget.h"
#include "qwt_dial.h"
#include "qwt_round_scale_draw.h"
#include "qwt_dial_needle.h"
#include "SpeedoMeter.h"

static QPalette colorTheme( const QColor& base )
{
    QPalette palette;
    palette.setColor( QPalette::Base, base );
    palette.setColor( QPalette::Window, base.darker( 150 ) );
    palette.setColor( QPalette::Mid, base.darker( 110 ) );
    palette.setColor( QPalette::Light, base.lighter( 170 ) );
    palette.setColor( QPalette::Dark, base.darker( 170 ) );
    palette.setColor( QPalette::Text, base.darker( 200 ).lighter( 800 ) );
    palette.setColor( QPalette::WindowText, base.darker( 200 ) );

    return palette;
}

static SpeedoMeter *g_dial = nullptr;
SpeedoMeterWidget::SpeedoMeterWidget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::SpeedoMeterWidget)
{
    ui->setupUi(this);

    setPalette( colorTheme( QColor( Qt::darkGray ).darker( 150 ) ) );

    g_dial = new SpeedoMeter(this);
    g_dial->setFrameShadow( QwtDial::Sunken );
    ui->verticalLayout->addWidget(g_dial);

    m_timerId = startTimer( 50 );
}

SpeedoMeterWidget::~SpeedoMeterWidget()
{
    delete ui;
}

void SpeedoMeterWidget::changeSpeed()
{
    static double offset = 0.8;

    double speed = g_dial->value();

    if ( ( speed < 7.0 && offset < 0.0 ) ||
        ( speed > 203.0 && offset > 0.0 ) )
    {
        offset = -offset;
    }

    static int counter = 0;

    switch( counter++ % 12 )
    {
        case 0:
        case 2:
        case 7:
        case 8:
            break;
        default:
            g_dial->setValue( speed + offset );
    }
}

void SpeedoMeterWidget::timerEvent(QTimerEvent *event)
{
    if ( event->timerId() == m_timerId )
    {
        changeSpeed();
        return;
    }
}