QOpenGLWidget QPainter::drawRect仅绘制四个箭头

void MyOpenGLWidget::paintEvent(QPaintEvent *event) {
    QOpenGLWidget::paintEvent(event);

    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing, true);

    QRectF rect(50, 50, 200, 100);
    painter.drawRect(rect);

    // 绘制箭头
    drawArrow(painter, rect.topLeft(), rect.topRight());
    drawArrow(painter, rect.topRight(), rect.bottomRight());
    drawArrow(painter, rect.bottomRight(), rect.bottomLeft());
    drawArrow(painter, rect.bottomLeft(), rect.topLeft());
}

void MyOpenGLWidget::drawArrow(QPainter &painter, const QPointF &start, const QPointF &end) {
    qreal arrowSize = 10;

    QLineF line(start, end);
    painter.drawLine(line);

    QPointF arrowP1 = line.p1() + (line.unitVector().normalVector() * arrowSize);
    QPointF arrowP2 = line.p1() + (line.unitVector().normalVector() * -arrowSize);
    QPolygonF arrowHead;
    arrowHead << line.p1() << arrowP1 << arrowP2;
    painter.drawPolygon(arrowHead);
}