[QWidget] How to save proporties?

[Macok]

How can I save proporties of QWidget while resizing?
For example I want QWidget's height to be always 3/4 of width.
Thanks in advance!

[Lykurg]

I don't an easy option for that, but you can reimpl QWidget::resizeEvent ( QResizeEvent * event ) and fix the proportion yourself.

[Macok]

Can you give me an example?
I tried something like this:

MyWidget::resizeEvent(QResizeEvent *e){
    e->size()->setWidth(...);
    e->size()->setHeight(...);
    QWidget::resizeEvent(e);
}

MyWidget::resizeEvent(QResizeEvent *e){
    e->size()->setWidth(...);
    e->size()->setHeight(...);
    QWidget::resizeEvent(e);
}

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But as I remember there wasn't even any difference...

[wysota]

There is also QWidget::heightForWidth().

[Macok]

Thanks, but how should I reimplement that QWidget::heightForWidth()?
I tried this:

int QWidget::heightForWidth(int w) const{
    return w*3/(double)4;
}

int QWidget::heightForWidth(int w) const{
    return w*3/(double)4;
}

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What's wrong?

[wysota]

That's not enough. You also have to tell the layout (through size policy) that you want to use heightForWidth. I'm also not sure if you can actually set it on a top level widget (you might have to set it on a child). Also remember this controlls the preferred width/height dependency. If you want to force it, you have to set a size constraint on the widget's layout. So if you don't know how to do that, reimplementing resizeEvent() might be a better (or at least faster to implement) idea. Your current implementation didn't work because QResizeEvent::size() returns a copy of the size object and after you modify the copy you need to set it back on the widget. It will work if you implement it properly.

[Macok]

Your current implementation didn't work because QResizeEvent::size() returns a copy of the size object and after you modify the copy you need to set it back on the widget. It will work if you implement it properly.

Thanks, but how can I do it?
Should I use setFixedPosition() in resizeEvent()?

[wysota]

No, you should use resize() or setGeometry() for example...

[Macok]

I tried, but it still doesn't work.
Here's the code for 1:1 proporties:

void GLWidget::resizeEvent(QResizeEvent *e){
    QResizeEvent *event;
    if(e->size().width()<e->size().height()){
        event=new QResizeEvent(QSize(e->size().height(), e->size().height()), e->oldSize());
        resize(e->size().height(), e->size().height());
    }
    else{
        event=new QResizeEvent(QSize(e->size().width(), e->size().width()), e->oldSize());
        resize(e->size().width(), e->size().width());
    }
    QGLWidget::resizeEvent(event);
}

void GLWidget::resizeEvent(QResizeEvent *e){
    QResizeEvent *event;
    if(e->size().width()<e->size().height()){
        event=new QResizeEvent(QSize(e->size().height(), e->size().height()), e->oldSize());
        resize(e->size().height(), e->size().height());
    }
    else{
        event=new QResizeEvent(QSize(e->size().width(), e->size().width()), e->oldSize());
        resize(e->size().width(), e->size().width());
    }
    QGLWidget::resizeEvent(event);
}

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If width is bigger than height, i set height to be the same as width and vice versa.
What's wrong?

[wysota]

Why are you creating a new resize event?

Please, if you use some method (like resizeEvent) please read its docs first. It's clearly stated the event is delivered after the widget has already been resized so changing the data sent to the base implementation won't do you any good especially that QWidget's resizeEvent() is empty.

void ...::resizeEvent(QResizeEvent *re){
  if(re->width()==re->height()) return; // avoid infinite loop
  int larger = qMax(re->width(), re->height());
  resize(larger, larger);
}

void ...::resizeEvent(QResizeEvent *re){
  if(re->width()==re->height()) return; // avoid infinite loop
  int larger = qMax(re->width(), re->height());
  resize(larger, larger);
}

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[Macok]

Thanks, now it's ok.

Why are you creating a new resize event?

If I don't callQGLWidget::resizeEvent(...) QGLWidget will not scale the scene displayed in it.


Finally, this works fine:

void GLWidget::resizeEvent(QResizeEvent *re){
  if(re->size().width()==re->size().height()) return; // avoid infinite loop
  int min = qMin(re->size().width(), re->size().height());
  resize(larger, larger);
 
  QGLWidget::resizeEvent(new QResizeEvent(QSize(min, min), re->oldSize()));
}

void GLWidget::resizeEvent(QResizeEvent *re){
  if(re->size().width()==re->size().height()) return; // avoid infinite loop
  int min = qMin(re->size().width(), re->size().height());
  resize(larger, larger);

  QGLWidget::resizeEvent(new QResizeEvent(QSize(min, min), re->oldSize()));
}

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But I have one more question.
When width of my window is bigger than height, widget will not be expanded on the whole window, but it'll be placed on the left side.
I'd like to place widget exactly in the middle of window's width.

Is there any simple way to reach this effect?
Maybe something with setGeometry()?
Thanks in advance.

[wysota]

You have a memory leak. As for the question, you already answered it.