Thanks for your engagement, but I don't seen go get anywhere.
I managed to implement a subclass of QGraphicsItem, but it does not draw, I have no idea why. Could you help me?
Qt Code: 
  1. #ifndef SHAPEITEM_H
  2. #define SHAPEITEM_H
  3.  
  4. #include <QtGui> 
  5. #include <QGraphicsItem>
  6. #include <QObject>
  7.  
  8. class ShapeItem : public QGraphicsItem
  9. {
  10.  
  11.  public:
  12. 				ShapeItem(void);
  13. 				ShapeItem(const QRect *rect);
  14. 				ShapeItem(const QPolygon *poly);
  15.  
  16. 	QRectF		boundingRect() const;
  17. 	QPainterPath shape(void) const;
  18.  
  19. 	virtual void		paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
  20. 						QWidget *widget);
  21. private:
  22.  
  23. 	int x0,y0,x1,y1,x2,y2,x3,y3;
  24. 	int xmin,ymin,xmax,ymax;
  25.  };
  26.  
  27. #endif
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Qt Code: 
  1. #include "shapeitem.h"
  2.  
  3. ShapeItem::ShapeItem(const QRect *rect)
  5. {
  6. 	x0 = rect->x();
  7. 	y0 = rect->y();
  8.  
  9. 	x1 = rect->x() + rect->width();
  10. 	y1 = y0;
  11.  
  12. 	x2 = x1;
  13. 	y2 = y0 + rect->height();
  14.  
  15. 	x3 = x0;
  16. 	y3 = y2;
  17.  
  18. 	xmin = x0;
  19. 	xmax = x1;
  20. 	ymin = y0;
  21. 	ymax = y2;
  22.  
  23. }
  24.  
  25. ShapeItem::ShapeItem(const QPolygon *poly)
  27. {
  28. 	poly->point(0,&x0,&y0);
  29. 	poly->point(1,&x1,&y1);
  30. 	poly->point(2,&x2,&y2);
  31. 	poly->point(3,&x3,&y3);
  32.  
  33. 	xmin = xmax = x0;
  34. 	ymin = ymax = y0;
  35.  
  36. 	if(x1<xmin) xmin = x1;
  37. 	if(x2<xmin) xmin = x2;
  38. 	if(x3<xmin) xmin = x3;
  39.  
  40. 	if(y1<ymin) ymin = y1;
  41. 	if(y2<ymin) ymin = y2;
  42. 	if(y3<ymin) ymin = y3;
  43.  
  44. 	if(x1>xmax) xmax = x1;
  45. 	if(x2>xmax) xmax = x2;
  46. 	if(x3>xmax) xmax = x3;
  47.  
  48. 	if(y1>ymax) ymax = y1;
  49. 	if(y2>ymax) ymax = y2;
  50. 	if(y3>ymax) ymax = y3;
  51.  
  52. }
  53.  
  54.  
  56. ShapeItem::boundingRect() const
  57. {
  58.          qreal penWidth = 1;
  59.          return QRectF(xmin - penWidth / 2, ymin - penWidth / 2,
  60.                        xmax + penWidth / 2, ymax + penWidth / 2);
  61. }
  62.  
  64. ShapeItem::shape() const
  65.  {
  67.      path.addRect(boundingRect());
  68.      return path;
  69.  }
  70.  
  71.  
  72. void
  73. ShapeItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
  74.                 QWidget *widget)
  75. {
  76.          painter->drawLine ( x0,y0,x1,y1 );
  77. 		 painter->drawLine ( x1,y1,x2,y2 );
  78. 		 painter->drawLine ( x2,y2,x3,y3 );
  79. 		 painter->drawLine ( x3,y3,x0,y0 );
  80. }
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Not at all optimized, as soon as it draws me anything in the scene, I will test different variants. At this stage, numItems=0 in myQGraphicsItems::drawIntems, so I'm stuck.

I am using it lile this:
Qt Code: 
  1. ShapeItem item(&outRect);
  2. 	scene->addItem(&item);
  3. 	//scene->addRect(outRect,solidBlue);
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The commented-out line draws as it should, while the active lines does not.