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

[franki]

Saturday 11 of December 2010 09:26:15 Mihail Naydenov napisał(a):
> Yes solution 2 is reasonable. The only problem is it is too general - it
> will affect the entire scene and all items.
>
> I will suggest making all doors, windows, etc items children of an empty
> parent item. All transformations applied to the parent will be propagated
> to the children,
> but you will still be able to use the same coordinates to draw items
> themselfs, these will not be changed, they are relative to the parent, not
> the scene or the view.
> In your init func, you draw aways on the same spot relative to the .jpg,
> then let the parent handle scaling and translating all items as a whole,
> relative to the scene or view.
> If you need to know when to modify this parent item based on scene/view
> variables you can monitor itemChange, ItemSceneChanged. When received the
> item is on stage and the view and scene are with the actual values.

Sorry for a long break before writing back.
I thought about this, that it can be a problem when dealing with animations. A 
few items are animated in a way that they move some 50 pixels. So this 50 
pixels is not always the same when I fitt to view.  Animations goes by 
changing Q_PROPERTY for this items. So how about making my items a children 
of the background image that represents the floor plan? Will it do any good? 
Background plan should transform himself when I fitt ro view with QRect which 
I set in the beginning (and placed this background image in the middle of 
QRect), am I right?

best regards
Marek 

>
> MihailNaydenov
>
> >From: Brian McKinnon <bpmckinnon.qt at gmail.com>
> >To: qt-interest <qt-interest at trolltech.com>
> >Sent: Fri, December 10, 2010 3:57:41 PM
> >Subject: Re: [Qt-interest] showEvent in QGraphicsView - question about
> > when to draw
> >
> >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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