自定义的Qt仪表盘控件

我做的仪表盘控件是个功能简单的显示控件。该控件在VS2015和Qt5.9上测试可用。它默认的显示范围是[0, 100]，不能修改它的显示范围，因为不同的数值显示在前界面上的效果不同，可能导致显示重叠。成员函数只有一个setValue方法用来设置当前显示值。

代码如下，头文件：

class MDashboard : public QWidget{    Q_OBJECTpublic:    MDashboard(QWidget* parent = nullptr);    void setValue(qreal ivalue);private:    void paintEvent(QPaintEvent *event) override;private:    const static int radius;    const static int maxv;    const static int minv;    qreal value;};

CPP文件：

const int MDashboard::radius = 80;const int MDashboard::minv = 0;const int MDashboard::maxv = 100;MDashboard::MDashboard(QWidget* parent) :    QWidget(parent){    value = 0;}void MDashboard::setValue(qreal ivalue){    value = ivalue;    update();}void MDashboard::paintEvent(QPaintEvent *){    QPainter painter(this);    painter.setRenderHint(QPainter::Antialiasing);    QPoint center(width() / 2, height() / 2);    painter.save();    /* 绘制背景圆形 */    painter.translate(center);    painter.setPen(Qt::NoPen);    painter.setBrush(QColor(143, 143, 143));    const int bkRadius = radius + 3;    painter.drawEllipse(QPoint(), bkRadius, bkRadius);    /* 绘制长短刻度线 */    painter.rotate(-135);    const int longStep = 10;    const int shortStep = 50;    for (int i = 0; i <= shortStep; i++)    {        /* 前80%绿色刻度线，后20%红色 */        painter.setPen((i < shortStep * 0.8) ? QColor(32, 243, 32) : QColor(243, 32, 32));        if (i % (shortStep / longStep) != 0)        {            QPoint p1(0, -(radius - 8));            QPoint p2(0, -radius);            painter.drawLine(p1, p2);        }        else        {            QPoint pl(0, -(radius - 12));            QPoint p2(0, -radius);            painter.drawLine(pl, p2);        }        painter.rotate(270.0 / shortStep);    }    /* 绘制表盘名字和它的背景矩形 */    painter.restore();    QFontMetrics fm = painter.fontMetrics();    int tx = center.x();    int ty = int(center.y() + (radius / 1.4142));    QString title = u8"仪表盘";    QSize tsz = fm.size(0, title);    QRect trect(QPoint(tx - tsz.width() / 2, ty - tsz.height() / 2), tsz);    painter.setPen(QColor(127, 127, 127));    painter.setBrush(QColor(173, 163, 163));    painter.drawRoundedRect(trect.adjusted(-6, -4, 6, 4), 3, 3);    painter.setPen(QColor(243, 243, 243));    painter.setBrush(Qt::NoBrush);    painter.drawText(trect, title);/* 绘制每个长刻度线对应的文字 */    painter.setPen(QColor(243, 243, 243));    const int hand = radius - 21;    for (int i = 0; i <= longStep; i++)    {        qreal angle = qDegreesToRadians(-135.0 + i * (270.0 / longStep));        QString etext = QString::number(minv + i * (maxv - minv) / longStep); /* 注意这里整形运算 */        QPointF dirVec(qSin(angle), -qCos(angle));        QPointF ecenter(center.x() + hand * dirVec.x(), center.y() + hand * dirVec.y());        QSize esz = fm.size(0, etext);        QRectF erect(QPointF(ecenter.x() - esz.width() / 2, ecenter.y() - esz.height() / 2), esz);        painter.drawText(erect, etext);    }    /* 绘制表盘指针 */    painter.save();    QPoint triangle[] = /* 向上的三角形 */    {        { -5, 0 },        { 0, 25 - radius },        { 5, 0 },    };    qreal degree = -135.0 + 270.0 * (value - minv) / (maxv - minv);    painter.translate(center);    painter.rotate(degree);    painter.setPen(Qt::NoPen);    painter.setBrush(Qt::red);    painter.drawPolygon(triangle, 3);    painter.setPen(QPen(QColor(213, 0, 0), 2));    painter.drawEllipse(QPoint(), 7, 7);    painter.restore();}