Extending QGraphicsLayout

Hello everyone.
I'm trying to extend QGraphicsLayout to build a new layout (let's called circleLayout). the program will be a plasma applet for KDE 4.2

First of all the example found in the documentation http://doc.trolltech.com/4.4/layout....ayout-managers doesn't works (i think it's because it's written to extend QLayout).
As explained in the page http://doc.trolltech.com/4.4/qgraphi...t.html#details i extended the method setGeometry() and sizeHint(). I took a look at source code of QGraphicsGridLayout and it doesn't seems that i need to extend other methods. Obviously, my code doesn't works :D
here's my code:

Code:

---

void circleLayout::setGeometry(const QRectF &r)
{
  kDebug()<<"Set Geometry!!";
 
  /*setting the real geometry*/
  QGraphicsLayout::setGeometry(r);
  /*taking the geometry*/
  QRectF effectiveRect = geometry();
  qreal left, top, right, bottom;
  getContentsMargins(&left, &top, &right, &bottom);
  /*adjust margins*/
  effectiveRect.adjust(+left, +top, -right, -bottom);
 
  kDebug()<<left<<","<<top<<","<<right<<","<<bottom;
 
  /*this is how qrectf works: Qrectf (xy top left corner, width ,height)*/
 
  /*if there are no elements in the list, view only the main element*/
  /*finding the center of the rectangular*/
  qreal centerX = left + (right/2);
  qreal centerY = top + (bottom/2);
  /*finding the radius of the circle*/
  qreal radius = 0;
  if(right > bottom)
    radius = bottom/2;
  else
    radius = right/2;
 
  /*the main element is located in the center and fill 1/3 of th space*/
  /*setting the rectf for the main element*/
  QRectF mainRect(centerX+radius/3, centerY+radius/3, radius*2/3, radius*2/3);
  mainElement->setGeometry(mainRect);
 
  kDebug() << "setting the main element geom";
 
  /*if i have only one element, i'll put in the top center*/
  if(list.size() == 1)
  {
    kDebug()<<"there is only one element";
    QGraphicsLayoutItem* element = list.at(0);
    /*putting this element at the top in the center*/
    QRectF elementRect(centerX+radius/3, centerY+radius, radius*2/3, radius*2/3);
    element->setGeometry(elementRect);
  }
  /*else i'll put the elements in the circle*/
  else if(list.size() > 1)
  {
    kDebug()<<"there are more elements, "<<list.size();
    for(int i=0; i<list.size(); i++)
    {
      /*this is the angle to rotate*/
      double angle = (2*PI*i)/list.size();
      /*than i made a rotation in center with the specified radius*/
      QMatrix rotMatrix(cos(angle), -sin(angle),
			sin(angle), cos(angle),
			 centerX,centerY);
      /*then i multiply the matrix with the point on the top of the circle*/
      qreal pointX;
      qreal pointY;
      /*rotation*/
      rotMatrix.map(centerX,centerY+(radius*2)/3,&pointX, &pointY);
 
      /*taking the i-esim element*/
      QGraphicsLayoutItem* element = list.at(i);
      /*try to put this element in the circle*/
      QRectF elementRect(pointX-radius/3, pointX-radius, radius*2/3, radius*2/3);
      element->setGeometry(elementRect);
    }
  }
}
 
QSizeF circleLayout :: sizeHint(Qt::SizeHint which, const QSizeF &constraint) const
{
     kDebug()<<"sizeHint!";
 
     QSizeF s(0,0);
     int n = list.count();
     if (n > 0)
         s = QSizeF(100,70); //start with a nice default size
     int i = 0;
     while (i < n) {
         QGraphicsLayoutItem *o = list.at(i);
         s = s.expandedTo(o->effectiveSizeHint(which, constraint));
         ++i;
     }
     return s ;
}

---

(the method sizeHint is semi-copied from QGraphicsGridLayout. i don't understand the true meaning of it)
So, here what's happens: i can compile everything without any problem, but i cannot see my object (maybe are too small?)
I'm expecting to find my objects placed around a main object (in the center)
As you may seen in the attachment, there are some dots in the center.. well, i think they're my objects! :eek:

here is the debug text i receive in my shell:

Code:

---

plasmoidviewer(29212) AdvancedMenuLayout::sizeHint: sizeHint!
plasmoidviewer(29212) AdvancedMenuLayout::sizeHint: sizeHint!
plasmoidviewer(29212) AdvancedMenuLayout::sizeHint: sizeHint!
plasmoidviewer(29212) AdvancedMenuLayout::setGeometry: Set Geometry!!
plasmoidviewer(29212) AdvancedMenuLayout::setGeometry: 4 , 4 , 4 , 4
plasmoidviewer(29212) AdvancedMenuLayout::setGeometry: setting the main element geom
plasmoidviewer(29212) AdvancedMenuLayout::setGeometry: there is only one element
QPainter::begin: Cannot paint on a null pixmap
QPainter::begin: Cannot paint on a null pixmap
QPainter::begin: Cannot paint on a null pixmap
QPainter::begin: Cannot paint on a null pixmap
QPainter::begin: Cannot paint on a null pixmap
QPainter::begin: Cannot paint on a null pixmap

---

The method setGeometry is never called!
Finally, here are my questions:
how can i extend QGraphicsLayout? what i have to do?
What i exactly have to implement inside sizeHint()? In what method i can specify where to place my elements?

thanks everyone in advance