[vtkusers] Saving image with transparent background from Qt

[Ignacio Fernández Galván]

On 06/03/18 18:50, Ben Boeckel wrote:
> ParaView does it this way:
> 
>      https://gitlab.kitware.com/paraview/paraview/blob/master/ParaViewCore/ServerManager/Rendering/vtkSMViewProxy.cxx#L474
> 
> Basically it screenshots twice, once with a black background and again
> with a white background to figure out what is "visible" and subtracts
> them.

Thanks, it's good to know at least I'm not doing something wrong. It 
seems, though, that ParaView is using a custom class 
vtkImageTransparencyFilter, so I'd have to reimplement it for plain VTK 
(note that I'm using python, so it's not just a matter of copying the 
cxx file).

Ignacio