How can we make a QRubberBand semi-transparent

Question

I have already used

setOpacity();

setAttribute(Qt:WA_TranseculentBackground:)

even i have tied all the available solution nothing has effect.

this is my code

void Physician::mouseMoveEvent(QMouseEvent *e)
{
    rubberBand->hide();
    bottomRight = e->pos();
    QRect rect = QRect(topLeft, bottomRight);
    rubberBand->setGeometry(rect);//Area Bounding
    QToolTip::showText(e->globalPos(), QString("%1,%2")
        .arg(rubberBand->size().width())
        .arg(rubberBand->size().height()), this);
}
void Physician::mousePressEvent(QMouseEvent *e)
{
    rubberBand->hide();
    if(e->x()<ui->videoShowLabel->x()||e->y()<ui->videoShowLabel->y())
    {
        selectWithInLabel.critical(0,"Error", "Select within the LABEL !");
        selectWithInLabel.setFixedSize(500, 200);
    }
    else{
        topLeft = e->pos();
        myPoint = ui->videoShowLabel->mapFromGlobal(this->mapToGlobal(e->pos()));
    }

}
void Physician::mouseReleaseEvent(QMouseEvent *e){
    rubberBand->setWindowOpacity(0.5);
    rubberBand->show();
}

void Physician::on_manualROIRadioButton_clicked()
{
    rubberBand = new  RubberBand(RubberBand::Rectangle, this);
}

What should i do to make rubberBand semiTransparent

Is this all still related to [this question](http://stackoverflow.com/questions/43559562/qrubberband-and-mplayer-in-qlabel)? — G.M., May 08 '17 at 10:31

Pavan Chandaka · Answer 1 · 2017-05-08T03:16:41.040

0

I assume you sub classed QRubberBand (RubberBand).

After calling the setWindowopacity the paint event is generated (http://doc.qt.io/qt-5/qwidget.html#windowOpacity-prop)

So redefine the paint event in RubberBand class.

Inside the paint event call "initStyleOption" (given below)

http://doc.qt.io/qt-5/qrubberband.html#initStyleOption

By calling "initStyleOption" you can set the rubber band parameters for drawing.

edited May 08 '17 at 03:16

answered May 08 '17 at 02:14

Pavan Chandaka

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score 0 · Answer 2 · answered May 08 '17 at 13:09

The real issue with making the QRubberband semi-transparent is that mplayer is painting on a window without Qt having any knowledge of it. Hence Qt itself cannot act as a compositor to generate the required effect.

One possibility would be to make the QRubberBand a top level window. That way the compositing is the responsibility of the underlying graphics system rather than Qt.

With that in mind try the following. Firstly a utility base class to manage the geometry...

class abstract_rubber_band {
public:
  virtual QRect get_geometry () const
    {
      return(QRect(m_parent->mapFromGlobal(widget().geometry().topLeft()), widget().size()));
    }
  virtual void set_geometry (const QRect &rect)
    {
      widget().setGeometry(map_rect(rect));
    }
protected:
  explicit abstract_rubber_band (QWidget *parent)
    : m_parent(parent)
    {}

  /*
   * @param point Coords relative to effective parent.
   */
  QPoint map_point (QPoint point) const
    {
      if (point.x() < 0)
        point.rx() = 0;
      else if (point.x() >= m_parent->width())
        point.rx() = m_parent->width() - 1;
      if (point.y() < 0)
        point.ry() = 0;
      else if (point.y() >= m_parent->height())
        point.ry() = m_parent->height() - 1;
      point = m_parent->mapToGlobal(point);
      return(point);
    }
  QRect map_rect (QRect rect) const
    {
      return(QRect(map_point(rect.topLeft()), map_point(rect.bottomRight())));
    }
private:
  QWidget &widget ()
    {
      return(dynamic_cast<QWidget &>(*this));
    }
  const QWidget &widget () const
    {
      return(dynamic_cast<const QWidget &>(*this));
    }
  QWidget *m_parent;
};

Now use the above as a base of the required rubber band class...

class rubber_band: public abstract_rubber_band,
                   public QRubberBand {
  using super = QRubberBand;
public:

  /*
   * @param parent Note that this isn't actually used as the
   *               parent widget but rather the widget to which
   *               this rubber_band should be confined.
   */
  explicit rubber_band (QWidget *parent)
    : abstract_rubber_band(parent)
    , super(QRubberBand::Rectangle)
    {
      setAttribute(Qt::WA_TranslucentBackground, true);
    }
protected:
  virtual void paintEvent (QPaintEvent *event) override
    {
      QPainter painter(this);
      painter.fillRect(rect(), QColor::fromRgbF(0.5, 0.5, 1.0, 0.25));
      QPen pen(Qt::green);
      pen.setWidth(5);
      painter.setPen(pen);
      painter.setBrush(Qt::NoBrush);
      painter.drawRect(rect().adjusted(0, 0, -1, -1));

      /*
       * Display the current geometry in the top left corner.
       */
      QRect geom(get_geometry());
      painter.drawText(rect().adjusted(5, 5, 0, 0),
                       Qt::AlignLeft | Qt::AlignTop,
                       QString("%1x%2+%3+%4").arg(geom.width()).arg(geom.height()).arg(geom.left()).arg(geom.top()));
    }
};

The above rubber_band class should almost be a drop in replacement for QRubberBand. The main difference is that rather than reading/writing its geometry with geometry/setGeometry you must use get_geometry/set_geometry -- those will perform the mapping to/from global coordinates.

In your particular case create the rubber_band with...

rubberBand = new  rubber_band(ui->videoShowLabel);

is there any solution to make semi-transparent that if i do not make any external class — Muhammad Athar Jan, May 10 '17 at 09:33
Create a `QRubberBand` as a top-level window (i.e. no parent) and call `setWindowOpacity`. But it'll then be up to you to manage its geometry. — G.M., May 10 '17 at 09:54

How can we make a QRubberBand semi-transparent

2 Answers2