[vtkusers] Combined on-screen and off-screen possible with VTK-7.0.0 on linux/X?

[Sophonet]

As a follow-up, I have done some more investigations myself and am still 
lost:

According to http://www.vtk.org/Wiki/VTK/OSMesa_Support, it seems that 
the legacy OSMesa library on linux systems is not needed anymore, but 
that software renderers (such as gallium llvm) can provide off-screen 
rendering themselves. Correct?

When looking at VTKROOT/CMake/vtkOpenGL.cmake, it appears (not perfectly 
sure though) that in this case VTK_OPENGL_HAS_OSMESA needs to be turned 
on, since this flag sets VTK_CAN_DO_OFFSCREEN to 1. However, it seems to 
me that VTK_CAN_DO_OFFSCREEN is not used anywhere else (did a thorough 
"grep" on that keyword in the source tree).

It seems that Marcus (Hanwell) was responsible for many of these changes 
in CMake - Marcus, can you help?

What I would like to do is (see my first e-mail below) to simultaneously 
use interactive rendering and (occasionally) off-screen rendering (for 
generating static images), which was possible on Linux in earlier 
versions of VTK (e.g. 5.10), but is not possible anymore.

Thanks,

        Sophonet


Am 2016-01-15 12:44, schrieb Sophonet:
> Dear list,
> 
> in my application, I would like to display a vtkRenderWindow for user
> interaction, but I also would like to use off-screen functionality
> simultaneously to render pre-defined views / snapshots that are shown
> as static images, like "thumbnails" for different datasets.
> 
> This was possible in VTK 5.10 on linux (by creating a dedicated
> vtkRenderWindow per thumbnail, setting OffScreenRenderingOn, rendering
> and capturing the resulting image with a vtkWindowToImageFilter).
> 
> In VTK-7.0.0.rc1, using the OpenGL rendering backend on Mesa 9.2.3, I
> now get a segfault with the following backtrace:
> 
> (gdb) bt
> #0  0x00007fffd045db90 in xcb_glx_get_string_string_length ()
>    from /usr/lib64/libxcb-glx.so.0
> #1  0x00007fffd0cce605 in ?? () from /usr/lib64/libGL.so.1
> #2  0x00007fffd0ccc2b6 in ?? () from /usr/lib64/libGL.so.1
> #3  0x00007fffd14cd086 in 
> vtkOpenGLExtensionManager::ReadOpenGLExtensions() ()
>    from
> /import/QUINTA/non-public/software/linux-install/quinta_gcc_debug/lib/libvtkRenderingOpenGL-7.0.so.1
> #4  0x00007fffd14cbd50 in vtkOpenGLExtensionManager::Update() ()
>    from
> /import/QUINTA/non-public/software/linux-install/quinta_gcc_debug/lib/libvtkRenderingOpenGL-7.0.so.1
> #5  0x00007fffd14cafd7 in
> vtkOpenGLExtensionManager::ExtensionSupported(char const*) ()
>    from
> /import/QUINTA/non-public/software/linux-install/quinta_gcc_debug/lib/libvtkRenderingOpenGL-7.0.so.1
> #6  0x00007fffd14ec8ea in vtkOpenGLRenderWindow::OpenGLInitContext() ()
>    from
> /import/QUINTA/non-public/software/linux-install/quinta_gcc_debug/lib/libvtkRenderingOpenGL-7.0.so.1
> #7  0x00007fffd14eae6d in vtkOpenGLRenderWindow::OpenGLInit() ()
>    from
> /import/QUINTA/non-public/software/linux-install/quinta_gcc_debug/lib/libvtkRenderingOpenGL-7.0.so.1
> #8  0x00007fffd1576932 in
> vtkXOpenGLRenderWindow::CreateOffScreenWindow(int, int) ()
> 
> Besides a remark that probably there could be better error handling
> than just letting the app crash without an exception being thrown, I
> would like to know if joint on-screen rendering and off-screen
> rendering is still possible somehow with VTK-7.0.0.
> 
> I have made two approaches when configuring via CMake: (i) Setting
> VTK_OPENGL_HAS_OSMESA=True (no effect, I think I remember that in
> earlier versions, this allowed OSMESA_INCLUDE_DIR etc. to be set; this
> is not the case anymore, so does this flag still do something? Note
> that for VTK 5.10 as mentioned above I did not have to set this
> explicitly), (ii) Setting USE_OFFSXCREEN_EGL=True - resulting in an
> error that this could not be combined with VTK_USE_X.
> 
> On Windows, combining on-screen and off-screen rendering as described
> in the second paragraph is possible.
> 
> Any suggestions would be welcome, the Wiki page I have found on this
> topic is not fully understandable to me
> (http://www.vtk.org/Wiki/VTK/OSMesa_Support; does this mean that I
> have to switch on VTK_OPENGL_HAS_OSMESA or not?...)
> 
> Thanks,
> 
>       sophonet
> 
> 
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