[vtkusers] flickering when using QT

[Anja Ende]

Hi,

I will try putting a transparant widget on top. I think that might be
efficient. Will keep the list updated if I make any progress.

Anja

On 16/10/06, Clinton Stimpson <clinton at elemtech.com> wrote:
>
>
> > From: "Anja Ende" <anja.ende at googlemail.com>
> > Subject: [vtkusers] flickering when using QT
> > To: VTK <vtkusers at vtk.org>
> >
> > Hi everyone,
> >
> > So, I have managed to render above a QVTKWidget window using QT.
> >
> > However, there is one nagging problem. So, I have a set of points that I
> can
> > interact with using the mouse and move them around. But whenever I move
> a
> > point around there is a lot of flickering. I am using Qt4 and double
> > buffering is on by default.
> >
> > Hoping that anyone who has more experience using QT with VTk might give
> some
> > advise on how to achieve flicker free rendering.
> >
> > Cheers,
> >
> > Anja
>
> Qt does double buffering by default.  And returning NULL for paintEngine()
> tells Qt "hands off" for this QWidget, which means it doesn't do double
> buffering.  The flickering you're seeing is a result of Qt doing double
> buffering, because you're giving it the QWidget::paintEngine().
>
> To compare with, the QGLWidget creates it's own QPaintEngine, instead of
> using QWidget::paintEngine().  All paint methods are implemented in OpenGL,
> and double buffering is probably turned off because it isn't a default paint
> engine.
>
> Way back during the Qt4 preview, Trolltech said they might make what
> you're trying to do easier, in Qt 4.1 or later.  4.2 is out and I don't
> know if they've done anything to help you.
>
> Here's a couple ideas, some without really knowing how well they'd work:
> 1. Find out how Trolltech was going to let us bypass the double buffer
> after Qt 4.0.  And find a solution based on that.  Here's the thread where
> they said that.
> http://lists.trolltech.com/qt4-preview-feedback/2005-04/thread00609-0.html
> 2. In your paintEvent(), do the QVTKWidget::paintEvent and do your
> painting into a QPixmap, and then combine the two.
> 3. Do your painting in VTK like everyone else.
> 4. Implement your own QPaintEngine in terms of VTK, or OpenGL, if you can
> assume you'll only ever use OpenGL.
> 5. Put a transparent widget on top of the QVTKWidget and do your painting
> on that.
>
> Clint
>
>
>


-- 
Cheers,

Anja
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