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Thread: Extending QGraphicsLayout

  1. 13th March 2009, 12:09 #1
    Darkman
    Darkman is offline Beginner
    Join Date
    Mar 2009
    Posts
    1
    Qt products
    Qt4
    Platforms
    Unix/X11

    Default 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
    here's my code:
    Qt Code: 
    1. void circleLayout::setGeometry(const QRectF &r)
    2. {
    3.   kDebug()<<"Set Geometry!!";
    4.  
    5.   /*setting the real geometry*/
    6.   QGraphicsLayout::setGeometry(r);
    7.   /*taking the geometry*/
    8.   QRectF effectiveRect = geometry();
    9.   qreal left, top, right, bottom;
    10.   getContentsMargins(&left, &top, &right, &bottom);
    11.   /*adjust margins*/
    12.   effectiveRect.adjust(+left, +top, -right, -bottom);
    13.  
    14.   kDebug()<<left<<","<<top<<","<<right<<","<<bottom;
    15.  
    16.   /*this is how qrectf works: Qrectf (xy top left corner, width ,height)*/
    17.  
    18.   /*if there are no elements in the list, view only the main element*/
    19.   /*finding the center of the rectangular*/
    20.   qreal centerX = left + (right/2);
    21.   qreal centerY = top + (bottom/2);
    22.   /*finding the radius of the circle*/
    23.   qreal radius = 0;
    24.   if(right > bottom)
    25.     radius = bottom/2;
    26.   else
    27.     radius = right/2;
    28.  
    29.   /*the main element is located in the center and fill 1/3 of th space*/
    30.   /*setting the rectf for the main element*/
    31.   QRectF mainRect(centerX+radius/3, centerY+radius/3, radius*2/3, radius*2/3);
    32.   mainElement->setGeometry(mainRect);
    33.  
    34.   kDebug() << "setting the main element geom";
    35.  
    36.   /*if i have only one element, i'll put in the top center*/
    37.   if(list.size() == 1)
    38.   {
    39.     kDebug()<<"there is only one element";
    40.     QGraphicsLayoutItem* element = list.at(0);
    41.     /*putting this element at the top in the center*/
    42.     QRectF elementRect(centerX+radius/3, centerY+radius, radius*2/3, radius*2/3);
    43.     element->setGeometry(elementRect);
    44.   }
    45.   /*else i'll put the elements in the circle*/
    46.   else if(list.size() > 1)
    47.   {
    48.     kDebug()<<"there are more elements, "<<list.size();
    49.     for(int i=0; i<list.size(); i++)
    50.     {
    51.       /*this is the angle to rotate*/
    52.       double angle = (2*PI*i)/list.size();
    53.       /*than i made a rotation in center with the specified radius*/
    54.       QMatrix rotMatrix(cos(angle), -sin(angle),
    55. 			sin(angle), cos(angle),
    56. 			 centerX,centerY);
    57.       /*then i multiply the matrix with the point on the top of the circle*/
    58.       qreal pointX;
    59.       qreal pointY;
    60.       /*rotation*/
    61.       rotMatrix.map(centerX,centerY+(radius*2)/3,&pointX, &pointY);
    62.  
    63.       /*taking the i-esim element*/
    64.       QGraphicsLayoutItem* element = list.at(i);
    65.       /*try to put this element in the circle*/
    66.       QRectF elementRect(pointX-radius/3, pointX-radius, radius*2/3, radius*2/3);
    67.       element->setGeometry(elementRect);
    68.     }
    69.   }
    70. }
    71.  
    72. QSizeF circleLayout :: sizeHint(Qt::SizeHint which, const QSizeF &constraint) const
    73. {
    74.      kDebug()<<"sizeHint!";
    75.  
    76.      QSizeF s(0,0);
    77.      int n = list.count();
    78.      if (n > 0)
    79.          s = QSizeF(100,70); //start with a nice default size
    80.      int i = 0;
    81.      while (i < n) {
    82.          QGraphicsLayoutItem *o = list.at(i);
    83.          s = s.expandedTo(o->effectiveSizeHint(which, constraint));
    84.          ++i;
    85.      }
    86.      return s ;
    87. }
    To copy to clipboard, switch view to plain text mode 
    (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!

    here is the debug text i receive in my shell:
    Qt Code: 
    1. plasmoidviewer(29212) AdvancedMenuLayout::sizeHint: sizeHint!
    2. plasmoidviewer(29212) AdvancedMenuLayout::sizeHint: sizeHint!
    3. plasmoidviewer(29212) AdvancedMenuLayout::sizeHint: sizeHint!
    4. plasmoidviewer(29212) AdvancedMenuLayout::setGeometry: Set Geometry!!
    5. plasmoidviewer(29212) AdvancedMenuLayout::setGeometry: 4 , 4 , 4 , 4
    6. plasmoidviewer(29212) AdvancedMenuLayout::setGeometry: setting the main element geom
    7. plasmoidviewer(29212) AdvancedMenuLayout::setGeometry: there is only one element
    8. QPainter::begin: Cannot paint on a null pixmap
    9. QPainter::begin: Cannot paint on a null pixmap
    10. QPainter::begin: Cannot paint on a null pixmap
    11. QPainter::begin: Cannot paint on a null pixmap
    12. QPainter::begin: Cannot paint on a null pixmap
    13. QPainter::begin: Cannot paint on a null pixmap
    To copy to clipboard, switch view to plain text mode 

    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
    Attached Images Attached Images
    Last edited by Darkman; 13th March 2009 at 12:39.
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