Fixed aspect ratio for a widget

florent.revelut

Hello,

In one of my projects, I had as a business requirement (flawed or not, this is out of scope) to have a fixed aspect ratio on my top level (and unique) widget.

Basically, user should select 4:3 or 16:9 then widget keeps aspect ratio.

I dug into QWidget documentation and code but I didn't manage to do this nor did I find any good solution.

I tried catching the resize event to hack ratio but it linked to some unsatisfactory results, I tried the setPreferedHeightForWidth, but it's well named, it works only in one way...

I finally lost faith and got rid of that requirement but now that this forum exist, does any one know a clean, good way of doing it ?

ZapB

Take a look at Qxt and in particular the "QxtLetterBoxWidget":http://libqxt.bitbucket.org/doc/tip/qxtletterboxwidget.html#details

tobias.hunger

Does "heightForWidth()":http://doc.qt.nokia.com/4.7-snapshot/qwidget.html#heightForWidth do what you need?

florent.revelut

@tobias
No it does not : it fulfills only a partial use case. Depending on the actual resize (shrinking only horizontally / only vertically - growing only vertically / only horizontally), the result can produce a wrong ratio.

Sorry, for not having linked the exact name, setPreferedHeightForWidth was what my mind remembered of height for width....

I'll try to make an example.

tobias.hunger

You will of course also need to set height for width in the size polizy, true. I have never tried it, not being the UI kind of guy, but I am pretty sure that should work.

florent.revelut

Easy enough, just try to compile that

@
#include <QWidget>
#include <QApplication>
#include <QSizePolicy>

class MyWidget:public QWidget
{
public:
  MyWidget():QWidget(){};
  ~MyWidget(){};
  virtual int heightForWidth ( int w ) const { return w*9/16;};
};

int main (int argv, char** argc)
{
  QApplication a(argv,argc);
  MyWidget w;
  QSizePolicy qsp(QSizePolicy::Preferred,QSizePolicy::Preferred);
  qsp.setHeightForWidth(true);
  w.setSizePolicy(qsp);
  w.show();

  a.exec(&#41;;
}

@
and resize the windows : it doesn't care about aspect ratio at all...