[Interest] [Development] QGraphicScene with thousands of QGraphicItems freezes the APP

[Samuel Rødal]

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