支持0到360°，360到0°的过度。
直接上代码，可以直接用，使用的paintevent事件实现的，没啥好讲的。

.cpp

void Widget::drawCourse(QPainter& p,QPen pen,QFont font)
{
    double currentNumber = m_ang;
    p.setBrush(Qt::black);
    p.drawRect(rect());

    //航向刻度图
    pen.setColor("#ffffff");
    pen.setWidth(2);
    p.setPen(pen);
    font.setPointSize(20);
    p.setFont(font);
    p.drawLine(0,0,width(),0);
    int mainScale = 360;
    double movePos = currentNumber*35-width()/2;
    //360前半截
    for (int i = 0; i < mainScale+1; ++i) {
        if (i%5 == 0)
        {
            pen.setWidth(2);
            p.setPen(pen);
            p.drawLine(0+i*35-movePos,0,0+i*35-movePos,26);
            p.drawText(0+i*35-30-movePos,33,60,30,Qt::AlignCenter,QString::number(i%360));
        }
        else
        {
            pen.setWidth(1);
            p.setPen(pen);
            p.drawLine(0+i*35-movePos,0,0+i*35-movePos,20);
        }
    }
    //0后半截,360前半截
    double startPt = 0;
    double showSpan = width()/35.00;
    if (currentNumber > 360 - showSpan || currentNumber < 360 - showSpan)
    {
        if (currentNumber > 360 - showSpan)
            startPt = (360 - currentNumber + showSpan/2)*35;
        else
            startPt = (showSpan/2 - currentNumber)*35 - 35*mainScale;
        for (int i = 0; i < mainScale+1; ++i) {
            if (i%5 == 0)
            {
                pen.setWidth(2);
                p.setPen(pen);
                p.drawLine(0+i*35+startPt,0,0+i*35+startPt,26);
                p.drawText(0+i*35-30+startPt,33,60,30,Qt::AlignCenter,QString::number(i%360));
            }
            else
            {
                pen.setWidth(1);
                p.setPen(pen);
                p.drawLine(0+i*35+startPt,0,0+i*35+startPt,20);
            }
        }
    }

    //航向中线
    p.setPen(QPen(QColor("#009af7")));
    p.setBrush(QBrush(QColor("#009af7")));
    QPolygon pol;
    pol<<QPoint(width()/2,72)<<QPoint(width()/2-17,103)<<QPoint(width()/2+16,103);
    p.drawPolygon(pol);
}