[vtkusers] offscreen rendering from gui application in vtk8/opengl2

[Ken Martin]

Another option might be to try switching to offscreen on your main render
window then switching it back to onscreen. I think the method is
SetUseOffscreenBuffers.  Then you don't have to copy any actors etc. That
might do the trick for you.

On Mon, Jul 9, 2018 at 7:38 AM, Patrick Bergeron <pbergeron at spiria.com>
wrote:

> The new OpenGL backend simply works differently than before.
>
> The other thing you can try is to debug vtk to try to detect a context
> change and to re-initialize the graphics resources.
>
> So when you switch Graphics contexts, they get destroyed and re created.
>
> You may try this with shaders first since it is your immediate problem.
> But I might expect you’d have to do it with textures too at least.
>
> Another way to get around it is to render into a different render target
> and read the contents of the image (if you can do with the same rendered
> size) by using a frame buffer object.
>
>
> Sent from my iPhone
>
> On Jul 9, 2018, at 07:23, Andreas Buykx <A.Buykx at dianafea.com> wrote:
>
> I had hoped I would not get this advice as it’s rather painful : we have
> heaps of actors and mappers with associated properties.
>
> This used to work before, was that a lucky accident?
>
>
>
>
>
> *From:* Patrick Bergeron <pbergeron at spiria.com>
> *Sent:* maandag 9 juli 2018 1:15
> *To:* Andreas Buykx <A.Buykx at dianafea.com>; 'vtkusers at public.kitware.com'
> <vtkusers at public.kitware.com>
> *Subject:* Re: offscreen rendering from gui application in vtk8/opengl2
>
>
>
> Hi Andreas,
>
>
>
> The actors and mappers use OpenGL resources that belong to an OpenGL
> context, but not all can be shared across multiple OpenGL contexts,
> especially if one context is software OpenGL (mesaGL?) and the other is
> not.
>
>
>
> Maybe VTK should have a way to clone the renderer and all its contents to
> do this automatically, or find a way to share shaders across contexts too...
>
>
>
>
>
> For now here is my recommendation, re-create your scene.
>
>
>
> - Create a new render window
>
> - Create a new renderer
>
> - Get all actors in the renderer,  and for each actor:
>
> - Create a new actor
>
> - Create a new mapper
>
> - Set the new mapper to the new actor
>
> - Get the input connection source of the mapper and set it to the new
> mapper
>
> - Copy the actor's rendering property to the new actor
>
> - Set the user transform of the old actor to the new actor.
>
>
>
> Set the active camera from y9our old renderer to new renderer
>
>
>
> Copy the lights too if necessary
>
>
>
> I think that is it!
>
>
> ------------------------------
>
> *From:* vtkusers <vtkusers-bounces at public.kitware.com> on behalf of
> Andreas Buykx <A.Buykx at dianafea.com>
> *Sent:* July 9, 2018 3:42:27 AM
> *To:* 'vtkusers at public.kitware.com'
> *Subject:* [vtkusers] offscreen rendering from gui application in
> vtk8/opengl2
>
>
>
> We recently switched our FEA application from vtk7.1 and the OpenGL
> backend to using 8.1 and the new OpenGL2 backend.
>
>
>
> With 7.1 we could make off-screen images from the gui application using a
> *temporary* off-screen render window, temporarily moving renderers from
> the GUI render window to the off-screen render window, render the image and
> then move all renderers back to the GUI render window.
>
> With vtk8.1 and OpenGL2 this causes OpenGL errors.
>
>
>
> I reproduced this with the attached script which on vtk8.1.1 and the
> current head leads to an openGL error:
>
>
>
> ERROR: In path-to/VTK-master/Rendering/OpenGL2/vtkOpenGLPolyDataMapper.cxx,
> line 1814
>
> vtkOpenGLPolyDataMapper (0x273dc00): failed after UpdateShader 1 OpenGL
> errors detected
>
>   0 : (1282) Invalid operation
>
>
>
> When the script is run with a global off-screen render window things work
> out fine.
>
>
>
> Is my approach wrong (temporary render window, moving renderers to it
> temporarily) or is this a bug?
>
>
>
> Thanks for your help!
>
>
>
> *DIANA FEA BV *
>
> *Software Developers and Analysis Consultants for Civil and Geotechnical
> Engineering *
>
>
>
> Delftechpark 19a, 2628XJ, Delft, The Netherlands
>
> Tel: +31 88 34262 15 (Direct) │ Tel: +31 88 34262 00 (Switchboard) │ Fax:
> +31 88 34262 99
>
> http://dianafea.com
>
>
>
>
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-- 
Ken Martin PhD
Distinguished Engineer
Kitware Inc.
101 East Weaver Street
Carrboro, North Carolina
27510 USA

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