QOpenGLWidget绘制线有时不可见或加粗

Question

我将QOpenGLWidget子类化，以绘制十字准线跟随鼠标。但是在QOpenGLWidget中进行绘制有点奇怪。当我上下移动鼠标时，水平线可能会消失或在某些高度上变为粗体。问题不会出现在QWidget中，为什么？

class OpenGLWidget : public QOpenGLWidget {
 public:
  OpenGLWidget(QWidget *parent = nullptr) : QOpenGLWidget(parent) {
    setMouseTracking(true);
  }
  void mouseMoveEvent(QMouseEvent *event) {
    m_mousePoint = event->pos();
    update();
  }
  void paintGL() {
    QPainter p(this);
    p.setPen(Qt::white);
    p.drawLine(QLineF(0, m_mousePoint.y(), width(), m_mousePoint.y()));
    p.drawLine(QLineF(m_mousePoint.x(), 0, m_mousePoint.x(), height()));
  }

  QPointF m_mousePoint;
};

the horizontal line looks bold
the horizontal line disapeared here