[Development] QGraphicScene with thousands of QGraphicItems freezes the APP

[Jose]

Thanks for your answer, I will try to play around with the optimization
flags, otherwise
I will paint everything in a single object.

Oh yes, my fault. I am sorry, I should have posted this on the
interest at mail list
from the beginning.

Cheers

2013/1/24 Samuel Rødal <samuel.rodal at digia.com>

> On 01/24/2013 08:35 AM, Samuel Rødal wrote:
> > On 01/23/2013 08:02 PM, Jose wrote:
> >> Hello,
> >>
> >> I am developing a Qt-based application. The main part of the application
> >> if a QGraphicView widget
> >> whose scene is populated with thousands (sometimes hundreds of
> >> thousands) of QGraphicItems, more
> >> precisely a subclass because to overload the "paint" function in order
> >> to draw a circle for each item.
> >
> > Each call to paint() involves a bit of set up / tear down of the
> > QPainter state as well as the overhead of a virtual function call. You
> > can get rid of some of the set up / tear down cost by setting the
> > DontSavePainterState optimization flag on the QGraphicsView, but then
> > you have to make sure that your items don't rely on a clean painter
> > state (and that they don't change the painter state).
> >
> > Also, make sure you don't have QGraphicsItem::ItemClipsToShape set on
> > any item in the parent chain.
> >
> > Still, it's always going to be faster to draw all the circles as a
> > single QGraphicsItem.
> >
> >> The problem is that the application basically freezes when I load a lot
> >> of items.
> >>
> >> Is this normal? Is there a limit on the number of  QGraphicItems that
> >> you can visualize?
> >>
> >> Also, if you want QGraphicItems to respond to a certain signal, do you
> >> need to connect
> >> the signal to an slot for each of the items?
> >
> > Doesn't sound like you want to do this for a hundred thousand items. Why
> > not have a controller item?
> >
> >> As an alternative, I can draw all the dots as a one single QGraphicItems
> >> which will solve
> >> the problem, I guees, but I would lose the interaction with the dots
> >> individually.
> >
> > Unless you allow interaction with the dots via that controller item.
>
> I didn't notice that this was the development@ list. Please use the
> interest@ list for questions that are about using Qt and not about
> developing Qt.
>
> --
> Samuel
>
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