[Qt-interest] aspect-ratio for graphs

[phil prentice]

Hi Sean
  With your help I am now closer to what I would like.  I think that part of 
my problem was the wish that the frame would always have an aspect ratio of 
1:1.  This mechanism does not achieve this. If you take your example you can 
obviously squeeze the vertical height to make the frames no longer square, I 
was half hoping that by some magic the horizontal width could also be made to 
reduce, but I think that asking to much (or is it?).
Anyway I guess it would be nice to be able to set the min-height of the main 
window to ensure that you cannot squeeze the height to the point of 
destroying the aspect ratio.  I tried re-implementing the sizeHint() function 
for the frame but that did not help.
Should I try catching the resize event (have not looked at this yet) and see 
if I can stop the main window from being resized to far using that method?  
My other  problem is that depending on the mode I need to display either 6 
graphs across the screen or just 3.

Thanks again for your help..I will keep playing

Phil
On Thursday 15 July 2010 12:30, phil prentice wrote:
> Thanks
>   Sean
> Thats brilliant I will try it now. Please ignore my last post...I will plug
> this into my example!!!!
> Thanks very much for your time
>
> Phil
>
> On Thursday 15 July 2010 11:44, Sean Harmer wrote:
> > On Thursday 15 July 2010 11:55:15 phil prentice wrote:
> > > Sorry Sean
> > >   Finger/Brain trouble...
> >
> > No worries.
> >
> > >   Indeed I am trying to use heightForWidth()...See my original mail
> > > which has a derived object within a layout.  I am cutting it down
> > > though and will continue to try and get it to work.  If no success I
> > > will mail the cut down version of my code. If I am successful I will
> > > also provide the code. Thanks for your help
> >
> > OK I have got an example of how to do this for you - see attached
> > tarball.
> >
> > The key is to set a suitable size policy in your custom widget (be it
> > derived from QWidget or from QGraphicsView) and to implement the int
> > heightForWidth( int w ) function.
> >
> > In the attached example I derived a class FixedAspectWidget from QWidget.
> > The ctor and heightForWidth() functions look like this:
> >
> > FixedAspectWidget::FixedAspectWidget(QWidget *parent) :
> >     QFrame(parent)
> > {
> >     setMinimumSize( 100, 100 );
> >     QSizePolicy policy( QSizePolicy::Preferred, QSizePolicy::Minimum );
> >     policy.setHeightForWidth( true );
> >     setSizePolicy( policy );
> > }
> >
> > int FixedAspectWidget::heightForWidth(int w) const
> > {
> >     return w;
> > }
> >
> > That is you have to call QSizePolicy::setHeightForWidth( true ). This
> > then tells any layout into which you place your widget that the layout
> > needs to call your widget's heightForWidth() function which in this case
> > simply returns the input width resulting in a square widget.
> >
> > This of course only provides you with a widget of fixed aspect ratio,
> > drawing your graphs with a fixed aspect ratio is a whole other problem
> > when you consider axis labels, ticks, titles, different coordinate
> > systems etc.
> >
> > HTH,
> >
> > Sean
> >
> > > Phil
> > >
> > > On Thursday 15 July 2010 10:34, you wrote:
> > > > Hi Phil,
> > > >
> > > > please reply to the list not to me personally.
> > > >
> > > > On Thursday 15 July 2010 11:22:10 phil prentice wrote:
> > > > > Thanks Sean
> > > > >
> > > > >   Will it help me with my aspect-ratio problem....because if it
> > > > > does then
> > > > >
> > > > > I would definitely use it.  Its the aspect-ratio problem I would
> > > > > like to solve...I need my graphs to have aspect-ratio of 1:1(inside
> > > > > a layout).  I could not see how QGraphicsView can help me there???
> > > > > Please tell me that I am wrong!!!
> > > >
> > > > QGraphicsView itself is just a QWidget so it will not support fixed
> > > > aspect ratio of the widget itself out of the box - you'll still need
> > > > to use something like heightForWidth() to implement that.
> > > >
> > > > You can make the graphs within your scene fixed aspect ratio quite
> > > > easily though. Can you provide a .ui file that shows the kind of
> > > > layout you would like?
> > > >
> > > > > I am still trying to play, but as of yet not getting anywhere
> > > >
> > > > I have no time to look at this right now but I may be able to later.
> > > >
> > > > Cheers,
> > > >
> > > > Sean
> > >
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> > > Qt-interest at trolltech.com
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>
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