QGraphicsItem Moving and crop

lietak

Hello,

I'm working with some QGraphicsSvgItems

Currently I have set every item in place.

Last feature is to move some of them when some event triggers.

I can now move the Items I want with:
svgItem->moveBy(0, 50);

Now the item looks funny after it goes down by 50 and overlaps the item underneath.
I would like to crop the bottom of the item by 50.

I tried:
svgItem->boundingRect().setBottom(-50);
It doesn't seem to have any effect.
Also tried several other functions which doesn't seem to do anything either.

While browsing the documentation of scenes, transformations and boundingrects etc. I'm getting a bit confused.

What is the best way to crop away part of the Item?

thanks.

Asperamanca

@lietak said in QGraphicsItem Moving and crop:

svgItem->boundingRect().setBottom(-50);

svgItem->boundingRect().setBottom(-50);

That really doesn't have any effect: You get a copy of the boundingRect, then change that copy. The result is not used, and therefore discarded. If you use the standard QGraphicsSvgItem, you don't control it's boundingRect - the item itself decides how big it is.
One way around:

Create your own QGraphicsItem-derived class where you can fully control the boundingRect - let's call it ClipperItem
Set the flag QGraphicsItem::ItemClipsChildrenToShape
Make the QGraphicsSvgItem a child of a ClipperItem

Adjust the ClipperItem's boundingRect as needed to show only the part of your Svg you want to show

Edit:
For a quick tryout, you can use QGraphicsWidget and use setGeometry to define it's size and position. However, for better performance (and if you don't need all the other features of QGraphicsWidget), I would implement a QGraphicsItem-derived class as final solution.

raven-worx

@lietak
For real clipping you can subclass QGraphicsSvgItem:

class MyGraphicsSvgItem : public QGraphicsSvgItem
{
public:
     MyGraphicsSvgItem(QGraphicsItem* parent = Q_NULLPTR) : QGraphicsSvgItem(parent)
     {
      this->setFlag( QGraphicsItem::ItemClipsToShape );
    }

    virtual QPainterPath shape() const Q_DECL_OVERRIDE {
        QPainterPath s = QGraphicsSvgItem::shape();
        QRectF clipRect = this->boundingRect();
              clipRect.setTop( clipRect.bottom()-50 );
        QPainterPath clipPath;
              clipPath.addRect(  clipRect );
         s = s.subtracted( clipPath );
        return s;
   }
};

(untested)

lietak

Ok thanks for the replies and help.

I kinda knew I would probably had to subclass it. Was mostly wondering if there was some other way.

So I'll try it out.

Edit.
I used @raven-worx solution
It works. Awesome.
Just made -50 as variable so I can change it per item :)