Resize window but preserve aspect ratio?

cincirin

Reimplement "QWidget::heightForWidth":http://doc.qt.digia.com/qt/qwidget.html#heightForWidth Return the prefered height for given width.

QMartin

Hi!

You can achieve it also with "horizontal layouts":https://qt-project.org/doc/qt-4.8/qhboxlayout.html and "vertical layouts":https://qt-project.org/doc/qt-4.8/qvboxlayout.html.

If you have an .ui, just group widgets with the tool buttons over the form, and if you has just typed code, implement something like this:

MainWindow.h:
@
#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QtGui> //I know this include here is a bad practice, but never mind, it's an example

class MainWindow : public QMainWindow
{
Q_OBJECT

public:
MainWindow(QWidget *parent = 0);
~MainWindow();

private:
QPushButton *one;
QPushButton *two;
QComboBox *three;
QComboBox *four;
QLineEdit *five;
QVBoxLayout *oneLayout;
QHBoxLayout *secondLayout;
QVBoxLayout *mainLayout;
QWidget *centralWidget; //here could be your sub-classed widget

};

#endif // MAINWINDOW_H@

MainWindow.cpp

@#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
centralWidget = new QWidget(this);
one = new QPushButton("Hello");
two = new QPushButton("Goodbye");
three = new QComboBox();
four = new QComboBox();
five = new QLineEdit("Now it is time");

oneLayout = new QVBoxLayout();
oneLayout->addWidget(one);
oneLayout->addWidget(two);

secondLayout = new QHBoxLayout();
secondLayout->addWidget(three);
secondLayout->addWidget(four);

mainLayout = new QVBoxLayout();
mainLayout->addWidget(five);
mainLayout->addLayout(oneLayout);
mainLayout->addLayout(secondLayout);

centralWidget->setLayout(mainLayout);

setCentralWidget(centralWidget);

}

MainWindow::~MainWindow()
{

}@

And your main.cpp

@#include <QApplication>
#include "mainwindow.h"

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();

return a.exec&#40;&#41;;

}@

And a .pro if you want to copy-paste:

@#-------------------------------------------------

Project created by QtCreator 2012-12-20T08:50:52

#-------------------------------------------------

QT += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = untitled
TEMPLATE = app

SOURCES += main.cpp
mainwindow.cpp

HEADERS += mainwindow.h@

Hope this->helps();

tobias.hunger

http://qt-project.org/doc/qt-5.0/qtwidgets/qwidget.html#heightForWidth might help here.

cincirin

[quote author="QMartin" date="1355990800"]You can achieve it also with "horizontal layouts":https://qt-project.org/doc/qt-4.8/qhboxlayout.html and "vertical layouts":https://qt-project.org/doc/qt-4.8/qvboxlayout.html.[/quote]

Hi @QMartin, I do not see how you can preserve widget aspect ratio in your example ...

QMartin

Hello @cincirin

It is done automatically, MainWindow resizes the centralWidget when mainWindow's size changes. So when I set a centralWidget and inside the central widget I specify one layout, these are resized preserving aspect ratio. Try it!

Regards

Sam

[quote author="QMartin" date="1355991441"]Hello @cincirin

It is done automatically, MainWindow resizes the centralWidget when mainWindow's size changes. So when I set a centralWidget and inside the central widget I specify one layout, these are resized preserving aspect ratio. Try it!

Regards[/quote]

I dont think that is the requirement as it is specified in the first post

bq. I want to preserve the mainwindow’s aspect ratio. if the window started as a square, it will stay square.

cincirin

Central widget doesn't force the width and the height to maintain the aspect ratio. For example @billconan wants widget to be always a square. So as me and @Tobias mentioned above, by simply reimplenting "QWidget::heightForWidth":http://doc.qt.digia.com/qt/qwidget.html#heightForWidth you can achieve this very easy

QMartin

Oh...

At first I thought everything in the window should preserve its ratio... without taking care about the initial size :S

Sorry then...

billconan

Thank you guys,

But I tried implementing heightForWidth, the function doesn't get called. I can still resize the window freely? Any ideas?

@
class MainWindow : public QWidget
{
Q_OBJECT

public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();

private:

QTimer timer;

void resizeEvent(QResizeEvent *);
void mouseReleaseEvent(QMouseEvent *);
virtual int heightForWidth ( int w ) { return w*9/16;};

private slots:
void onTimeOut();
};
@

@
MainWindow::MainWindow(QWidget *parent) :
QWidget(parent)
{
QSizePolicy qsp(QSizePolicy::Preferred,QSizePolicy::Preferred);
qsp.setHeightForWidth(true);
setSizePolicy(qsp);
}
@

cincirin

Hi, first you forgot const modifier for heightForWidth function. Second I didn't tested on top level window which seems to be the problem, see "Trading Height for Width":http://doc.qt.digia.com/qq/qq04-height-for-width.html