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I have 2 custom widgets inheriting from QGLWidget and I aim to show the same scene from 2 different views using these widgets. For this I share the first widget with the second widget. However this requires a custom constructor than the compiled UI file provides. Such as

   // The line I mention from Compiled UI file
    widget_2 = new SideGlWidget(widget);
    // What I actually want this line to be
    widget_2 = new SideGlWidget(widget, MainScreen);

Some suggests to set such additional parameters later using an init function. Then how do I set shareWidget member of QGLWidget? here is the contructor of SideGlWidget

SideGlWidget::SideGlWidget(QWidget *parent,QGLWidget * shareWidget)
    : QGLWidget(parent,shareWidget)
{

}

Any comments and edits are welcome.

in4001
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  • which language is this? looks like c++? – user3528438 Aug 25 '15 at 12:40
  • exactly, the first line is from ui_mainwindow.h which is thanks to compilation of UI file, the second line is what I need – in4001 Aug 25 '15 at 12:42
  • Showing the code of the constructor of `SideGlWidget` will be helpful. I assume `SideGlWidget` subclasses from `QGLWidget`, then you need to add a second constructor that fordwards `shareWidget` to the base class constructor. – user3528438 Aug 25 '15 at 12:48
  • I edited the question with that information – in4001 Aug 25 '15 at 13:07

2 Answers2

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When dealing with Qt widgets generated through a UI file, you can't change how the constructor of your custom widget is called.

You have two options then :

  • Make a default second parameter to the SideGlWidget
  • Add a init( sharedWidget) method to your widget and call it after setupUi() (most likely in your main window's constructor). You can thus pass your parameter to the side widget before it is shown.

This forum post explains it in detail.

Looking at your problem at a higher level, I would suggest using some kind of shared object that holds common data to the two widgets and use either inheritance or composition instead of defining one widget to use another.

Louen
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  • The only problem with the init(sharedWidget) approach is that I couldnt find a way to set "sharedWidget" other than in the constructor. Maybe it is a private field without a setter? Regarding your general suggestion, with your way then how do you share the context? Do you suggest to store the context as a static class'es member which could make it globally accessible. – in4001 Aug 25 '15 at 13:54
  • * Shared Widget has to be somewhere in the data members of your class, so if there's no setter you can add one yourself. * As for my suggestion, I was saying that if your two widgets are doing the same thing (i.e. showing an Open GL scene) only with different parameters (the camera position), it would seem logical for them to be instances of the same class, or at least sharing a base class. – Louen Aug 25 '15 at 15:37
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Here is the official and latest solution to this problem from http://doc.qt.io/qt-5/qopenglwidget.html:

When multiple QOpenGLWidgets are added as children to the same top-level widget, their contexts will share with each other. This does not apply for QOpenGLWidget instances that belong to different windows.

Therefore by inheriting from QOpenglWidget instead of QGlWidget you dont have to deal with context sharing at all. Beware that updategl function is replaced with update function.

in4001
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