QWidget::setMask: bug &/or help for workaround

[ataffard]

Hi,

I'm working on a set of classes implementing various button shapes that can be re-oriented (rotated & translated) for various set of layout (eg table, circles etc..)
In order to do this, the classes inherit from QPushButton and the paintButton method is reimplemented.

Since only the shape of the button (ellipse, trapezoid etc..) should be active when the mouse goes over it etc... and since the button can be rotated on itself to arrange it on a layout, I'm making use of setMask function to make only the shape of the button visible.

This approach works fine for rectangle, trapezoid shapes but for circle or ellipse shapes the application become extremely slow and the button have some hatched marks (see attached snapshots). The problem clearly come from setMask since when commented out the app. runs fine and the buttons look ok.

I'm using Qt 4.3.0 and also tried with 4.4.0 in case it was a bug and got fixed, but the problem remain.

Could anyone help me to determine if I'm doing something wrong (see attached code snippet)
or if this is a Qt issue in which case any advice/suggestion on how to workaround this without loosing the functionality and a smooth running app. would be more than welcome.

One possible workaround would be not to not use a mask but use a function that figure out if the mouse is within the button shape boundaries. Unfortunately, this would cause problem when the button are rotated and placed onto a layout due to the overlap in the QWidget rectangle. So it doesn't seem that this approach would workout.

Thanks in advance for the help.
Anyes

//__________________________________________________________________________________________________
void ShapedButtonEllipse::paintButton(QPaintEvent* )
{
  updateButtonSize();
 
  QPointF center = QPointF(width()/2., height()/2.); 
 
  QStylePainter painter(this);  
  painter.setRenderHint(QPainter::Antialiasing);
 
  painter.save();//save the painter state
  painter.translate(center); //translate coordinate system to center of shape  
 
  /*
    Test for state changes 
  */
  QColor button_color;
  if(this->isEnabled())
    {
      m_hovered ? button_color = b_highlight : button_color = b_color;
      if(m_pressed)
	  button_color = b_highlight.darker(250);
    }
  else
      button_color = QColor(50, 50, 50);
 
  /*
    Rotate painter wrt to button center if the button has been rotated
  */
  if(rot_angle != 0)
    painter.rotate(-rot_angle);
 
  /*
    Draw the button
  */
  painter.setPen(QPen(QBrush(Qt::black), bw, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin)); //button outline 
  QLinearGradient gradient(0., 0., 0., height()); //button inside color gradient 
  gradient.setColorAt(0., button_color);
  gradient.setSpread(QGradient::PadSpread);
  painter.setBrush(gradient);
 
  QPainterPath outline;
  outline.addEllipse(-s_width/2, -s_height/2, s_width, s_height); //button outline shape
 
  /*
    Define visible/active region (add 2pixel extra all around)
  */
  const qreal b = bw/2 + 4;
  QRegion maskedRegion((int)(-s_width/2 -b  ), (int)(-s_height/2 -b  ),
  		       (int)( s_width   +b*2), (int)( s_height   +b*2), QRegion::Ellipse); 
  if (rot_angle != 0)
    {
      QMatrix matrix;
      matrix.rotate(-rot_angle);
      maskedRegion = maskedRegion * matrix;
      maskedRegion.translate(center.toPoint());
    }
  else
    {
      maskedRegion.translate((int)center.x(),(int)center.y());
    }
 
  setMask(maskedRegion); //Funny looking after masking, very slow ????
  painter.drawPath(outline);
 
  painter.restore(); 
 
  /*
    Add button text if any
  */
  QString text = this->text();
  if(!text.isNull())
    {
      QFont font = this->font();
      painter.setFont(font);
      painter.setPen(t_color);
      painter.setOpacity(1.0);
      painter.drawText(0, 0, width(), height(), Qt::AlignCenter, text);
    }
 
}

//__________________________________________________________________________________________________
void ShapedButtonEllipse::paintButton(QPaintEvent* )
{
  updateButtonSize();
  
  QPointF center = QPointF(width()/2., height()/2.); 
  
  QStylePainter painter(this);  
  painter.setRenderHint(QPainter::Antialiasing);

  painter.save();//save the painter state
  painter.translate(center); //translate coordinate system to center of shape  
  
  /*
    Test for state changes 
  */
  QColor button_color;
  if(this->isEnabled())
    {
      m_hovered ? button_color = b_highlight : button_color = b_color;
      if(m_pressed)
	  button_color = b_highlight.darker(250);
    }
  else
      button_color = QColor(50, 50, 50);
  
  /*
    Rotate painter wrt to button center if the button has been rotated
  */
  if(rot_angle != 0)
    painter.rotate(-rot_angle);

  /*
    Draw the button
  */
  painter.setPen(QPen(QBrush(Qt::black), bw, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin)); //button outline 
  QLinearGradient gradient(0., 0., 0., height()); //button inside color gradient 
  gradient.setColorAt(0., button_color);
  gradient.setSpread(QGradient::PadSpread);
  painter.setBrush(gradient);
  
  QPainterPath outline;
  outline.addEllipse(-s_width/2, -s_height/2, s_width, s_height); //button outline shape

  /*
    Define visible/active region (add 2pixel extra all around)
  */
  const qreal b = bw/2 + 4;
  QRegion maskedRegion((int)(-s_width/2 -b  ), (int)(-s_height/2 -b  ),
  		       (int)( s_width   +b*2), (int)( s_height   +b*2), QRegion::Ellipse); 
  if (rot_angle != 0)
    {
      QMatrix matrix;
      matrix.rotate(-rot_angle);
      maskedRegion = maskedRegion * matrix;
      maskedRegion.translate(center.toPoint());
    }
  else
    {
      maskedRegion.translate((int)center.x(),(int)center.y());
    }
  
  setMask(maskedRegion); //Funny looking after masking, very slow ????
  painter.drawPath(outline);
  
  painter.restore(); 
  
  /*
    Add button text if any
  */
  QString text = this->text();
  if(!text.isNull())
    {
      QFont font = this->font();
      painter.setFont(font);
      painter.setPen(t_color);
      painter.setOpacity(1.0);
      painter.drawText(0, 0, width(), height(), Qt::AlignCenter, text);
    }
 
}

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