[vtkusers] Render function's in-deterministic performance

[Siddharth Vikal]

I've tried the suggestions from Sebastien and Navneeth i.e. upgrading to
VTK 5.8, and calling modified, however the problem remains unsolved.

Any insights into why 'render' should behave erratically? The rendering
time alone, measured before and after call of renwin->render is varying
from 6-7 msecs at most times to 50-60 msecs at other times!

David, any thoughts?

regards,
Siddharth

On Tue, Dec 6, 2011 at 10:17 PM, Navneeth Subramanian
<navneeth.s at gmail.com>wrote:

> Hi Siddharth,
> Perhaps you are seeing a race-condition between the camera capture
> thread & the vtk render thread ?
> Can you force call ->Modified() on the vtkImageData object at the end
> of the camera refresh to see if that helps.
>
> best,
> navneeth
>
> > ------------------------------
> >
> > Message: 16
> > Date: Tue, 6 Dec 2011 19:35:52 +0530
> > From: Siddharth Vikal <siddharthvikal at gmail.com>
> > Subject: [vtkusers] Render function's in-deterministic performance
> > To: vtkusers at vtk.org
> > Message-ID:
> >        <
> CADM22yxyGDvhiWBogiqTV7M5B_ZExryetZCQzSxPn6jwGRhjPw at mail.gmail.com>
> > Content-Type: text/plain; charset="iso-8859-1"
> >
> > Hi,
> >
> > Let me first describe the set-up. I'm using a quad core, linux box with
> vtk
> > 5.4. I'm using Qt for GUI, thus QVTKWidget. I'm trying to visualize image
> > frames (1280 x1280 pixels) being captured from a camera device. The
> > anticipated frame rate is 30 fps. I've 'capture frame' functionality
> > happening in a separate thread. A minimal vtk pipeline is set up using
> > vtkImageData, vtkImageMapper, vtkActor2D. Each time a new frame arrives,
> > update is callled on the vtk pipeline and the main thread running Qt, is
> > notified to perform render operation using paint event of QVTKWidget. For
> > synchronization, mutex is used. This setup seems to work just fine except
> > from the performance predictability standpoint.I've put timers in place
> to
> > measure time taken for each step.
> >
> > The problem is, the paint call (or eventually 'render' call) is not
> > behaving deterministically. For some frames, render completes within 6-10
> > milliseconds, but for others, inexplicably, it starts taking 50-70
> > milliseconds!! Now with new frame arriving at every 33 milliseconds (30
> > fps), I start loosing frames. I've tried the setup using vtkImageActor
> > (therefore without vtkImageMapper, vtkActor2D) as well, but with similar
> > behavior.
> >
> > I don't understand why is render taking 60-70 milliseconds? The data is
> > ready to be rendered. The in-deterministic aspect is even more worrying.
> >
> > Can someone please help? It'll be greatly appreciated.
> >
> > regards
> > Siddharth
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