Qwt 使用QwtDial绘制汽车仪表盘

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;
    }
}