[Qt-interest] multiple glwidget interaction

[John McClurkin]

Sajjad wrote:
> Hello John,
> 
> I have declared a SharedWidgetData class that contains all  the matrices 
> that need to be shared between 2 gl widgets.
> 
> Then i created a singleton class and instantiate one instance of the 
> SharedWidgetData  in the constructor of the top level window constructor 
> as follows:
> 
> 
> ******************************************************************************
> Singleton<SharedWidgetData>::init(new SharedWidgetData());
> 
> ******************************************************************************
> 
> Then i send the pointers of the newly instantiated object to both the 
> widgets so that both the widgets can access and update the matrices as 
> necessary.
> 
> But the program crashes and while debugging it i found that the program 
> gives a segmentation fault in the above line.  Singleton class is 
> full-proof i believe since it has been used in another API and it has 
> been quite functional so far.
> 
> 
> 
> Any hint to track  the issue?

The Singleton class may be fool proof and may have been used 
successfully elsewhere, but it may be giving you problems in your 
instance. Try just creating an instance of your SharedWidgetData class;

SharedWidgetData *p = new SharedWidgetData();

If this also crashes, you have a problem in your constructor. If not 
there must be a problem with the Singleton implementation.
> 
> 
> Regards
> Sajjad
> 
> 
> 
> 
> 
> On Tue, Jul 6, 2010 at 8:54 PM, John McClurkin <jwm at nei.nih.gov 
> <mailto:jwm at nei.nih.gov>> wrote:
> 
>     Sajjad wrote:
>      > Hello forum,
>      >
>      > I have two separate classes inherited from QGLWidget and both  the
>      > classes need to share and update the projection , modelview and
>     inverse
>      > matrices . These matrices are defines as follows:
>      >
>      > I get  the modelview matrix by
>      >
>      > glGetDoublev(GL_MODELVIEW_MATRIX, modelview); And that modelview
>     matrix
>      > will be shared and updated by both the QGLWidget subclasses. I
>     need to
>      > have the following matrices declared, but not sure where to
>     declare them.
>      >
>      > GLdouble modelview[16]
>      > GLdouble projection[16]
>      > GLdouble inverse[16]
>      >
>      >
>      > I have declared the above matrices in one of the widget and i need to
>      > pass the contents of these matrices to another gl widget. Do i
>     have to
>      > declare another three arrays in that widget as well?
>      >
>      >
>      > I also need to set several signal and slots, like when ever the
>     any of
>      > the matrices changes the matrices will be passed with  the
>     corresponding
>      > slots. The slots may be of the same widget or the other widget.
>      >
>      >
>      >
>     I would define a class containing the three arrays with functions to get
>     and set their values and signals that could be emitted by those
>     functions whenever the values were accessed. Then instantiate just one
>     instance of that class.
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