[vtkusers] Rendering QVTKWidget into QPixmap

[Julien Finet]

Hi Christian,

Here is what we do in CTK to grab a QVTKWidget:
https://github.com/commontk/CTK/blob/master/Libs/Visualization/VTK/Widgets/ctkVTKWidgetsUtils.cpp

Please note that it means that QVTKWidget::cachedImage must be turned on.

Hth,
Julien.

On Wed, Feb 8, 2012 at 7:16 AM, Christian Lackas <lackas at invicro.com> wrote:

> Hi Everybody,
>
> we are using VTK in a Qt-based application of ours and employ QVTKWidget
> for this. To allow the user to store rendered data as images, we use
> code such as:
>
>    class VRenderer: public QVTKWidget {
>        Q_OBJECT
>        public:
>            ...
>            QPixmap grabImage() {
>                QPixmap pixmap( size() );
>                render( &pixmap );
>                return pixmap;
>            }
>        ...
>    };
>
> and then use the QPixmap object to produce an image file (which aligns
> well with our non-VTK-based rendering widgets).
> On Mac OS X, as well as Linux and many Windows systems this does work
> pretty well. Unfortunately, we do have a couple of Windows system
> (Vista, 7, 32- and 64-bit, but not consistently on one platform) where
> above code produces merely an all-black image.
> I assume this has something to do with how the graphic card driver
> handles the OpenGL drawing (or something along this line, e.g.
> asynchronous processing, where we grab the image to early, etc...).
>
> I already tried using functions such as
> vtkRenderWindow::WaitForCompletion(),
> however, as the documentation suggest that was not useful here, calling
> vtkRenderWindow::Render() explicitly myself, etc...
>
> Is there a way to make sure that a QVTKWidget renders and actual image
> into my pixmap?
>
> Or should I start using vtkRenderWindow::GetRGBAPixelData() instead?
>
> Thanks for any hints.
>  Christian
>
> --
> http://www.invicro.com/  http://www.spect-ct.com/
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