Qt drawing David's triangle electricity

直接上code
void paintEvent(QPaintEvent *event)
{
Q_UNUSED(event);
QPainter painter(this);

    QRect rect0 = QRect(0,0,500,500);
    painter.drawRect(rect0);
    QRect rectB = QRect(-1,-1,501,501);
    painter.drawRect(rectB);




    //画三角形
    QLine line1 = QLine(QPoint(250.0f,80.0f),QPoint(400.0f,350.0f));
    QLine line2 = QLine(QPoint(250.0f,80.0f),QPoint(100.0f,350.0f));
    QLine line3 = QLine(QPoint(100.0f,350.0f),QPoint(400.0f,350.0f));
    painter.drawLine(line1);
    painter.drawLine(line2);
    painter.drawLine(line3);

    painter.drawText(245,75,"PD");


    //画刻度
    QLine Graduation1_1 =  QLine(QPoint(115.0f,324.0f),QPoint(125.0f,324.0f));
    QLine Graduation1_2 =  QLine(QPoint(129.0f,297.0f),QPoint(139.0f,297.0f));
    QLine Graduation1_3 =  QLine(QPoint(145.0f,270.0f),QPoint(155.0f,270.0f));
    QLine Graduation1_4 =  QLine(158.0f,243.0f,168.0f,243.0f);
    QLine Graduation1_5