[Qt-interest] [Qt-Interest] Painting outside paintEvent in QT4.5 : Widget painting can only begin as a result of a paintEvent

[shivam priyadarshi]

Hi Alex and Thiago,

Thank you very much for replying back.  Actually in my GUI code i am
painting on Scroll Area (QAbstractScrollArea in Qt4.5 and Q3ScrollView in
support function).  So as paintEvent function of QAbstractScrollArea says,
always open a painter on the viewport(). So Painter is always opened on
viewport().

So if i follow approach  A does this mean  i should open  the painter on
Qpixmap  or  Qimage rather than on viewport.

I am doing like following which worked fine with 3.3

void QucsView::MMovePainting(QMouseEvent *Event)
{
Qpainter painter(viewport());
setPainter(&painter);
update();
}

where setPainter is function where painting is done and QucsView class
inherit Q3ScrollView.

Regards:
Shivam




On Mon, Jun 1, 2009 at 10:20 PM, Malyushytsky, Alex <alex at wai.com> wrote:

> According to how I see it:
>
> Approach A (simplest)
> ------------------------------------------------------------------
> Instead of painting to the widget, paint to the QPixmap or QImage.
> Update the widget when painting done.
>
> + minimum changes to the paining code.
> - sometimes update of the whole widget from image is inefficient and it
> might be not that easy to implement it efficiently.
>   And things got worse when you like to see evolution of the drawing on the
> screen instead of the result.
>
>
> Approach B (never tried, but it looks promising, if I don't make any
> mistake about it functionality)
> ------------------------------------------------------------------
> Paint to QPicture, store QPicture object(s).
> Call update when required, use QPicture object to draw in the paint event.
>
> I can't recommend it, cause I never tried, but it seems more powerful.
>
>
> Best regards,
>
> Alex
>
>
>
>
> -----Original Message-----
> From: qt-interest-bounces at trolltech.com [mailto:
> qt-interest-bounces at trolltech.com] On Behalf Of Thiago Macieira
> Sent: Saturday, May 30, 2009 2:52 PM
> To: qt-interest at trolltech.com
> Subject: Re: [Qt-interest] [Qt-Interest] Painting outside paintEvent in
> QT4.5 : Widget painting can only begin as a result of a paintEvent
>
> shivam priyadarshi wrote:
> >I have this kind of code structure at various places in application. I
> >have tight schedule, it will be great help if you can help me with make
> >it work with QT4.5 with painting outside paintEvent.
>
> You have to refactor your code so that you paint only inside the
> paintEvent.
> --
> Thiago Macieira - thiago.macieira (AT) nokia.com
>  Senior Product Manager - Nokia, Qt Software
>      Sandakerveien 116, NO-0402 Oslo, Norway
>
>
>
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