[vtkusers] VTK and QT headaches

[Aashish Chaudhary]

Hi Alex,

On Tue, Dec 14, 2010 at 9:38 AM, Alex Southern <mrapsouthern at gmail.com>wrote:

>  Aashish,
>
> Thanks for your reply. I am visualizing wave propagation over time using
> imageData, i require to be able to rotate and zoom using the mouse while the
> image data is being constantly updated and rendered on screen. It is the
> mouse interaction that is very jerky. I am using the new GTX 480 (so I know
> that my system is not the problem here - as my test case is very small as
> well).
>
> So yes I need two threads, the main thread and myThread, as the user
> interaction is an important aspect here. Although I take your point that it
> is easier not to use threads, but in that case I lose the ability to
> interact with the scene while the simulation is running.
>
> With regards the link you sent me.... im really not sure how to apply that
> to my own problem, could you or anyone else elaborate?
>
> I have to look into the VTK code to really if it is possible but the idea
is that you create main context, create another context sharing the main
(OpenGL implementation specific to OS calls) or share lists,  you use this
second context in your worker thread, but you would have to make this
context current, create GL objects emit the signal, make the context current
in other thread and follow on.

Its not straightforward and I myself have to look at the exact calls as it
been a very long time.  There could be some issues depending on the OS you
are running this.


>  Thanks
> Alex
>
>
> On 14.12.2010 16:24, Aashish Chaudhary wrote:
>
> Hi Alex,
>
>  You context is not shared between threads as its indicated in the error.
> This is nothing new and you can find lot more information if you google for
>
>
>  "OpenGL share context between threads"
>
>  It works in second case because Qt is doing the job of signalling the
> function in other thread in thread safe manner.
>
>  But looking at your sample code, I am not sure what kind of interaction
> issues you are having...
>
>  Do you really need two threads? If you do (as I guess you might be
> loading data in one and displaying in other), there could be ways around
> it..
>
>  May be this link helps giving you more insight:
>
>
> http://hacksoflife.blogspot.com/2009/08/creating-opengl-textures-or-vbos-on.html
>
>
>
>
> On Tue, Dec 14, 2010 at 8:45 AM, Alex Southern <mrapsouthern at gmail.com>wrote:
>
>> Hi,
>>
>> Im running a QThread event loop and trying to execute a
>> vtkInteractorWindow->Render() command after each iteration. I have tried two
>> approaches so far but neither work well.
>>
>> The First approach, gives a VTK error and is based on something like this:
>> At the initialization stage I pass a pointer to iren. Then in the run()
>> function I execute iren->Render();
>>
>> class myThread : public QThread
>> {
>>    Q_OBJECT
>>
>>  public:
>>     vtkRenderWindowInteractor *iren;
>>     void run();
>>    {
>>        for (int i = 0; i < 2000; i++)
>>        {
>>            // process some data
>>            iren->Render();
>>        }
>>    }
>> };
>>
>> This compiles but gives the error in the vtkOutputWindow on each call of
>> Render()....
>>
>> ERROR: In ..\..\Source\VTKGit\Rendering\vtkWin32OpenGLRenderWindow.cxx,
>> line 247
>> vtkWin32OpenGLRenderWindow (05153168): wglMakeCurrent failed in
>> MakeCurrent(), error: The requested resource is in use.
>>
>> The second approach gives no errors, but results in a very jerky
>> interaction. It is implemented by emitting a signal from the for loop after
>> every iteration. The threads myRender() signal is connected to a
>> updateRenderWindow() slot function i.e.
>>
>> class myThread : public QThread
>> {
>>    Q_OBJECT
>>
>>  public:
>>     void run()
>>    {
>>        for (int i = 0; i < 2000; i++)
>>        {
>>            // process some data
>>            emit myRender();
>>        }
>>    }
>>  signals:
>>     void myRender();
>> };
>>
>> class myWindow : public QMainWindow
>> {
>>    Q_OBJECT
>>
>> public:
>>    myThread Td;
>>    vtkRenderWindowInteractor *iren;
>>
>> public slots:
>>    void updateRenderWindow()
>>    {
>>        iren->Render();
>>    }
>> }
>>
>>
>> Does anyone have any suggestions as to how I can improve either of these
>> methods to give a better interaction?
>>
>> Thanks
>> Alex
>>
>>
>>
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>
>
>
> --
> | Aashish Chaudhary
> | R&D Engineer
> | Kitware Inc.
> | www.kitware.com
>
>
>


-- 
| Aashish Chaudhary
| R&D Engineer
| Kitware Inc.
| www.kitware.com
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