selection in a lot of polylines with QGraphicsView doesn't work fine

Question

In Qt, there is no "QGraphicsPolylineItem", so I have to implement it form QGraphicsItem. I reimplement 'paint' and 'boundingRect' functions.In 'paint()' function, I just simply draw all lines in the polyline. It's OK without any user's interaction. For selection and movable function, I reimplement the 'QPainterPath* shape()' function like this:

QPainterPath ContourLineShape::shape() const
  {
    QPainterPath path;
    QPointF p0=this->poly.at(0)->at(0);
    path.moveTo(p0.x(),p0.y());
    foreach(QPointF p,poly)
        path.lineTo(p.x(),p.y());
        return path;
  }

but the result is wrong. when i click on a polyline ,it always selects another. Then I try to implement the selection myself, like this:

void GraphicsView::mousePressEvent ( QMouseEvent * event )
{
    int x=event->pos().x();
    int y=event->pos().y();

    QList<QGraphicsItem *>items=this->items(x-5,y-5,10,10,Qt::IntersectsItemShape);
    for(int i=items.size()-1;i>=0;i--)
    {
        QGraphicsItem *item=items.at(i);

        if(item->type()==QGraphicsItem::UserType+4)//UserType+4 is my polyline type.
        {
            item->setSelected(true);
            return; //one shape has been selected.
        }
    }
}

This solution looks like right, but it's not exact. If a polyline like this:

      ----------------------
     |
     |      o<-click here   |
     |                      |
     |  /\   /\             |
     | /  \ /  \ /-----------
      /    V    V

The click point is far from the bound lines ,but the shape still can be selected(it's not what I wanted). Even if I changed the selection mode to Qt::ContainsItemBoundingRect or Qt::ContainsItemShape.., the result is still wrong. Is there any easy way to solve this problem?Or,must I calculate the distances from 'click point' to all the segments to decide if it's selected?

Thanks!

Answer 1

Does calling setFlags(QGraphicsItem::ItemClipsToShape) help?