Implementing a butcon

[Theo Landman]

Thanks for the various hints.
I ended up sub-classing QMenu and then implemented my own paintEvent():

void
JQLineTypeMenu::paintEvent(
   QPaintEvent* event
   )
{
   QPainter p(this);
   QRegion emptyArea = QRegion(rect());
 
   //draw the items that need updating..
   foreach ( QAction* action, actions() )
   {
      QRect adjustedActionRect = actionGeometry(action);
      if ( !event->rect().intersects(adjustedActionRect) )
           continue;
 
      //set the clip region to be extra safe (and adjust for the scrollers)
      QRegion adjustedActionReg(adjustedActionRect);
      emptyArea -= adjustedActionReg;
      p.setClipRegion(adjustedActionReg);
 
      QStyleOptionMenuItem opt;
      initStyleOption(&opt, action);
      opt.rect = adjustedActionRect;
      drawMenuItem(&opt, &p, action);
    }
   ...
}
void
JQLineTypeMenu::drawMenuItem(
   const QStyleOptionMenuItem* opt,
   QPainter* p,
   const QAction* action
   )
{
   bool act = opt->state & QStyle::State_Selected;
   QBrush fill = opt->palette.brush(act ? QPalette::Highlight : QPalette::Button);
   p->fillRect(opt->rect, fill);
 
   QPen linePen(static_cast<Qt::PenStyle>(action->data().toInt()));
   linePen.setWidth(3);
   linePen.setBrush(opt->palette.brush(act ? QPalette::HighlightedText : QPalette::ButtonText));
   p->setPen(linePen);
   p->drawLine(opt->rect.left(), opt->rect.center().y(), opt->rect.right(), opt->rect.center().y());
}

void
JQLineTypeMenu::paintEvent(
   QPaintEvent* event
   )
{
   QPainter p(this);
   QRegion emptyArea = QRegion(rect());

   //draw the items that need updating..
   foreach ( QAction* action, actions() )
   {
      QRect adjustedActionRect = actionGeometry(action);
      if ( !event->rect().intersects(adjustedActionRect) )
           continue;
      
      //set the clip region to be extra safe (and adjust for the scrollers)
      QRegion adjustedActionReg(adjustedActionRect);
      emptyArea -= adjustedActionReg;
      p.setClipRegion(adjustedActionReg);

      QStyleOptionMenuItem opt;
      initStyleOption(&opt, action);
      opt.rect = adjustedActionRect;
      drawMenuItem(&opt, &p, action);
    }
   ...
}
void
JQLineTypeMenu::drawMenuItem(
   const QStyleOptionMenuItem* opt,
   QPainter* p,
   const QAction* action
   )
{
   bool act = opt->state & QStyle::State_Selected;
   QBrush fill = opt->palette.brush(act ? QPalette::Highlight : QPalette::Button);
   p->fillRect(opt->rect, fill);

   QPen linePen(static_cast<Qt::PenStyle>(action->data().toInt()));
   linePen.setWidth(3);
   linePen.setBrush(opt->palette.brush(act ? QPalette::HighlightedText : QPalette::ButtonText));
   p->setPen(linePen);
   p->drawLine(opt->rect.left(), opt->rect.center().y(), opt->rect.right(), opt->rect.center().y());
}

To copy to clipboard, switch view to plain text mode 

The various actions in the menu held the different pen styles (using QAction::setData()). I then instanced my JQLineTypeMenu for the toolbar.
Note: if you need also the scrollbar and/or tear-off support then it is better creating a custom QWidget and insert instances of those in the menu through QActionWidget.
The whole Qt library is full of private data members that sometimes makes C++ deriving a big cut&paste exercise