[Qt-interest] showEvent in QGraphicsView - question about when to draw

[Brian McKinnon]

Method number 2 is definitely the right way to do it.  It terms of the
drawing position as it rescales there shouldn't be a problem as long as you
enable antialiasing on the graphicsview you should be fine.  The text may
become an issue, so you may want to store a list of text objects in your
scene and scale the text sizes as your view changes.  Although there may be
a more efficient way of doing that... like storing a text sting in your
graphicsitems and have the views paintevent scan through the items in the
scene and draw the requested text on the view during the paintevent.  I
think that may end up making your text much less scale dependent.  But I'm
just spitballing here.

2010/12/10 franki <franki at franki.eu.org>

> Thursday 09 of December 2010 19:54:37 Mihail Naydenov napisał(a):
> > It is hard for me to track you thoughts. What exactly are you trying to
> do.
> > "During initialization of my class", what class?
> > Why not draw on paint()? All will be initialized then.
>
> Hello,
>
> Maybe I start with explaining something about my app.
> Application is based on QStackedWidget, and almost every page has
> QGrapvicsView stretched onto pages. Views are displaying plan of some
> building, each floor and so on. Plan itself is a jpg image with walls,
> doors,
> etc. Onto this plan I draw items like: windows, doors, radiators (for
> central
> heating) and so one. Some of this items are animated, eg. when You open the
> window, signal is sent to app through rs232 and window is opening itself.
> Anyway, it's crucial for me to draw these items exacly at specific points.
> The problem is: I run this application on 18" widescreen panel or on
> laptop,
> with different sizes and resolutions, so I can't set size of QGraphicsView
> to
> be constant (eg. in Qt Designer). The plan (I mean jpg image) is also
> scaled
> to fitt in the view. QGraphicsScene must be as big as QGraphicsView,
> without
> scrollbars. Because of this, sometimes I need to draw let's say window item
> at point 200px,250px and sometime at 300px,350px depending on the size of
> the
> screen.
> So I can think of two solutions of this problem.
> 1. I start drawing all items after I get signal from sublcassed
> QGraphicsView
> on showEvent, then I know size, I set scene to be almost size of
> QGraphicsView, and start drawing. However, now when I think about this it's
> still mess, because I would need to calculate where to paint items.
> 2. Second idea is to set scene before showEvent, little bigger than jpg
> with
> floor plan (without scaling it), place the jpg in the center of the scene,
> then draw items in their positions (which would be constant and always
> known
> because I know size of this jpg) and then on showEvent I should call
> fittInView with QRect set at the size of the previously created scene. I
> assume that every item, and background jpg, will be rescaled to fitt in
> view
> without scrollbars, but again I may be wrong, because this is really my
> first
> app, so I simply don't know, until I try. Moreover I was affraid that
> rescaling will make some of items little bit off their positions or for
> example fonts will not look nice after that.
>
> You said: "Why not draw on paint()" - You meant paint... what? paintEvent
> or
> something else? I honestly don't know what you meant by that.
> Please someone advise me.
>
> best regards
> Marek
>
> >
> >
> > ----- Original Message ----
> >
> > > From: franki <franki at franki.eu.org>
> > > To: qt-interest <qt-interest at trolltech.com>
> > > Sent: Thu, December 9, 2010 6:08:45 PM
> > > Subject: [Qt-interest] showEvent in QGraphicsView - question about when
> > > to
> >
> > draw
> >
> > > Hello,
> > >
> > > I had a problem determinig size of QGraphicsScene, and from what I  had
> > > read so
> > >
> > > far, size of QGraphicsView should be determined in showEvent  because
> > > before this event happend geometry has some bogus data.
> > > So I did  it that way, but show event is comming late, far after class
> > > itself had been  initialized. During initialization of my class, I used
> > > to draw an items  inside scene, but now when showEvent is comming late
> > > what should I do? eg.  Send a signal from inside subclassed
> > > QGraphicsView, which triger some function in base class to start
> drawing
> > > items?
> > > Is that a right way, or  are there some other options?
> > >
> > > best  regards
> > > Marek
> > > _______________________________________________
> > > Qt-interest  mailing list
> > > Qt-interest at trolltech.com
> > > http://lists.trolltech.com/mailman/listinfo/qt-interest
>
>
>
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