[vtkusers] How create an offscreen render window in VTK ?? Please Help

[Sylvain Jaume]

Hi Deepak,

OffScreenRendering will not work on Linux since it is only implemented 
for vtkWin32OpenGLRenderWindow. Are you developing on Linux?

Cheers,
Sylvain

Deepak Roy wrote:

> Hello,
>  
> I tried vtkRenderWindow::OffScreenRenderingOn today but it does not work.
>  
> It would be really helpful if you could provide any examples.
>  
> I turned it on and used vtkWindowToImageFilter to save a snapshot of 
> the OffScreenRenderWindow to an image file( JPEG ) on disk but the 
> image comes out to be a snaphot of the desktop when the code is executed.
>  
> I am using the VTK + QT library written by Carsten Kibler. I suspect 
> if that is giving the problem. Because My Application is developed 
> with QT and VTK. So there is already a QT + VTK render window in which 
> the model is being displayed. I am creating the offscreen render 
> window after that, so i suspect there are some conflicts.
> Because if i turn the offscreenrendering to off ( which is the default 
> ), the render window is not visible, which is not normally expected.
>  
> I am using offscreen rendering to find the volume enclosed between two 
> surfaces.
>  
>  --- First i render the surface behind ---> extract the z-buffer of 
> the offscreen window.
>  
> ---- Second i remove the surface behind and new render the front 
> surface alone ---> extract the z-buffer again
>  
> ----- Subtracting both the Z-buffers would give me the volume.
>  
> I earlier used vtkMassProperties but it does not give good results. 
> Hence i resorted to the z-buffer technique.
>  
> Here is the code i used for the offscreen rendering:
>  
> ************************************************************************************************
>  
> vtkOpenGLRenderer *pOffScreenRenderer = vtkOpenGLRenderer::New();
>  
> vtkRenderWindow *pOffScreenRenderWindow = vtkOpenGLRenderWindow::New();
> pOffScreenRenderWindow->OffScreenRenderingOn();
> pOffScreenRenderWindow->AddRenderer( pOffScreenRenderer );
> pOffScreenRenderWindow->Start();
> pOffScreenRenderWindow->SetSize( wx , wy );
> pOffScreenRenderWindow->Render();
>  
> // render a surface now
> pOffScreenRenderer->AddActor( pSurfaceActor );
> pOffScreenRenderer->Render();
> pOffScreenRenderWindow->Render();
>  
> // save a snapshot to disk
> vtkWindowToImageFilter *pWindowImageFilter = 
> vtkWindowToImageFilter::New();
> pWindowImageFilter->SetInput( pOffScreenRenderWindow );
> vtkJPEGWriter *pImageWriter = vtkJPEGWriter::New();
> pImageWriter->SetInput( pWindowImageFilter->GetOutput() );
> pImageWriter->SetQuality( 100 );
> pImageWriter->SetFileName( "coons_image.jpg" );
> pImageWriter->ProgressiveOff();
> pImageWriter->Write();
> pImageWriter->Delete();
>  
> *************************************************************************************************
>  
> Is there anything wrong with the code ?
>
> Please Help !!!!!
>  
> Thanks in Advance.
>  
> Regards
>  
> Deepak Roy
>  
>
> */Sylvain Jaume <sylvain.jaume at kitware.com>/* wrote:
>
>     Hi Deepak,
>
>     Have you tried vtkRenderWindow::OffScreenRenderingOn?
>     http://www.vtk.org/doc/nightly/html/classvtkWindow.html#803e4f1aba85b796a0f17b0ec84093f9
>
>     Cheers,
>     Sylvain
>
>     Deepak Roy wrote:
>
>     > hello everybody,
>     >
>     > Do you know how to create an offscreen vtk render window in VTK ?
>     >
>     > I want to render into the off screen render window and then get its
>     > z-buffer using GetZbufferData
>     >
>     > () and work on its z-buffer.
>     >
>     > Or is there an offscreen buffer similar to vtkRenderWindow.
>     >
>     > Please Help.
>     >
>     > Thanks in advance.
>     >
>     > Regards,
>     >
>     > Deepak
>     >
>     >
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