Qt编写自定义控件：圆弧形进度条

class Widget2 : public QWidget
{
    Q_OBJECT

public:
    Widget2(QWidget *parent = nullptr);
    ~Widget2();
    void setPercentage(qreal value);

protected:
    void paintEvent(QPaintEvent *event) override;
private:
    qreal percentage{0};
};

void Widget2::setPercentage(qreal value)
{
    this->percentage = value;
    update();
}

int getStartAngle(int angle)
{
    if(angle <= 180)
    {
        return (180 - angle) / 2 * 16;
    }
    else
    {
        return -(angle - 180) / 2 * 16;
    }
}

void Widget2::paintEvent(QPaintEvent *event)
{
    auto rect = this->rect();
    qreal realSize = qMin(rect.width(), rect.height());
    qreal width = 50;

    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing);
    painter.translate(rect.width()/2, rect.height()/2);
    painter.scale(realSize/1000, realSize/1000);

    QRectF rectangle(-500.0, -500.0, 1000.0, 1000.0);
    rectangle.adjust(width,width,-width,-width);

    int angle = 270;
    int spanAngle = angle * 16;
    int startAngle = getStartAngle(angle);

    //滑槽
    painter.setPen(QPen(QColor("#c8c8c8"),width,Qt::SolidLine,Qt::RoundCap,Qt::RoundJoin));
    painter.drawArc(rectangle.adjusted(10,10,-10,-10), startAngle, spanAngle);

    startAngle = startAngle + spanAngle;
    spanAngle = -angle * percentage * 16;

    painter.setPen(QPen(QBrush(QGradient(QGradient::StrongBliss)),width,Qt::SolidLine,Qt::RoundCap,Qt::RoundJoin));
    painter.drawArc(rectangle.adjusted(10,10,-10,-10), startAngle, spanAngle);

    painter.setPen(Qt::black);
    painter.setFont(QFont("隶书",50));
    painter.drawText(rectangle,Qt::AlignCenter,QString("%1%").arg(percentage * 100));
}