[vtkusers] Animation without polling?

Fri Sep 11 08:48:51 EDT 2009

Hi John,
unfortunately I no hardly anything about MFC. I was hoping for a system independent solution.

But maybe somebody can help to apply your suggestion to the (linux) X windows system?
An equivalent of "::PeekMessage( 
&msg, NULL, 0, 0, PM_NOREMOVE )" is readily available (XNextEvent or XCheckIfEvent).
But I have no idea, what AfxGetThread()->PumpMessage() and AfxGetThread()->OnIdle() are supposed to do exactly, not to speak about implementation with X.
Moreover, I don't see, which vtk object will handle the queued messages in your code snippet. My limited understanding of vtkAnimationScene is that it only handles animation events. You'd need a vtkRenderWindowInteractor in addition, which would be in charge of the mouse/key event, don't you?. Can I find a complete example somewhere, which shows your snippet in context?

Regards,
Guido

From: jcplatt at dsl.pipex.com
To: guidorodriguez1952 at hotmail.com
CC: vtkusers at vtk.org
Subject: Re: [vtkusers] Animation without polling?
Date: Fri, 11 Sep 2009 09:51:30 +0100

Hi,

After rendering each frame, allow any queued messages to 
be processed -

case vtkCommand::AnimationCueTickEvent:

{

    .....

    self->Render();

    // Allow interaction with the scene and 
UI.

    self->Pump();

}

break;

This is an MFC implementation of Pump() -

BOOL Pump()

{

    MSG msg;

    while ( ::PeekMessage( 
&msg, NULL, 0, 0, PM_NOREMOVE ) )

    {

        if ( ! 
AfxGetThread()->PumpMessage() )

        {

            ::PostQuitMessage( 0 
);

return FALSE;

        }

    }

    LONG lIdle = 0;

    while ( 
AfxGetThread()->OnIdle( lIdle++ ) );

    return TRUE;

}

This seems to works OK on Windows.

HTH

John.

  ----- Original Message ----- 
  From: 
  Guido Rodriguez 
  To: mark.gooding at gmail.com 
  Cc: vtkusers at vtk.org 
  Sent: Friday, September 11, 2009 8:57 
  AM
  Subject: Re: [vtkusers] Animation without 
  polling?

Mark, thank you.
I have found an example, how 
  vtkAnimationCues and vtkAnimationScenes can be used, at http://www.vtk.org/pipermail/vtkusers/2005-April/079340.html. 
  I didn't know these animation classes before, and find them very 
  helpful.

But for the specific problem, how to run an animation parallel 
  to listening to mouse/key events, I don't see how this helps, yet.
The 
  example above starts animation with
  scene->Play();
How can 
  this coexist with a call to vtkRenderWindowInteractor::Start()?
Both calls 
  run their own event loop, the one handling animation events, the other 
  handling interaction events.

I'm looking forward to your more detailed 
  information.

Regards,
Guido

> Date: Thu, 10 Sep 2009 
  17:06:39 +0100
> Subject: Re: [vtkusers] Animation without 
  polling?
> From: mark.gooding at gmail.com
> To: 
  guidorodriguez1952 at hotmail.com
> CC: vtkusers at vtk.org
> 
> 
  you shouldn't have to write a complete vtkRenderWindowInteractor, just
> 
  add an observe to handle AnimationCueTickEvents
> 
> 
  http://www.vtk.org/doc/nightly/html/classvtkCommand.html
> 
> i'll 
  try to send you more detailed information later. I don't have my
> 
  software which did animation to hand right now.
> 
> Mark
> 

> 
> 2009/9/10 Guido Rodriguez 
  <guidorodriguez1952 at hotmail.com>:
> > Dear VTK 
  users/developers,
> > I ask for guidance, how animated visualization 
  is done right with VTK. What
> > I have in mind is an application 
  which calculates, let's say, a temperature
> > field, which changes 
  in time. Whenever the field is completely calculated
> > for the next 
  time step, the visualization should be updated. In parallel,
> > the 
  user should be able to work with the mouse/key controls to rotate the
> 
  > view, zoom, interact with 3D widgets, etc.
> >
> > The 
  obvious way would be to run VTK in one thread, and the calculation in
> 
  > another. Each finished calculation step would notify VTK to update. But 
  it
> > doesn't work like this. At least not with the X windows 
  system. When I call
> > some pipeline's Update() function from a 
  different thread, I get an "invalid
> > thread access".
> 
  >
> > Next attempt. I implement an event buffer, which is written 
  to by the
> > calculation thread, and which is read from by the VTK 
  thread. This works
> > like a charm. Now VTK can check whether an 
  update is necessary and get the
> > required data from the event 
  buffer. But _when_ does VTK check for updates?
> > I can't seem to 
  find a solution which sets VTK to sleep until either a
> > mouse/key 
  event happens or until the calculation thread releases some lock,
> > 
  simply because any VTK callback waiting for notification from a 
  different
> > thread would stop VTK from reacting to mouse/key events 
  during this period.
> >
> > The only solution I can see is 
  to add a timer event like every 10 ms, which
> > checks the event 
  buffer for updates. This works, but is it recommended?
> > Threading 
  libraries have introduced locks and notification to avoid the
> > 
  overhead from polling at interactive rates for events that may occur 
  only
> > every few seconds. How can good multithreading programming 
  styles be applied
> > to VTK?
> >
> > I hope the 
  problem is clear. Can a different thread trigger pipeline updates
> > 
  under X windows? Or do I have to write my own 
  vtkRenderWindowInteractor?
> >
> > Regards,
> > 
  Guido
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