[vtkusers] vtk 7.x.x: offscreen rendering without DISPLAY variable not possible anymore with vtkXOpenGLRenderWindow

[Michael Bachmann]

Hi all!

Using vtk 6 it was still possible to render images offscreen on a headless machine on Linux (no DISPLAY) with a vtkXOpenGLRenderWindow instance.
The only things which were necessary were a working version of osmesa library in the OpenGL installation and the function OffscreenRenderingOn() needed to be called on the vtkRenderWindow instance.

Using VTK 7 (7.0.0.rc1 and the latest development version (7.1.0)) this is not possible anymore.

In VTK 6 the pre-processor define VTK_OPENGL_HAS_OSMESA was used in vtkXOpenGLRenderWindow.cxx, which allowed to perform offscreen rendering on headless machines.
In VTK 7 the pre-processor define VTK_OPENGL_HAS_OSMESA has been replaced by VTK_USE_OSMESA such that it is only possible to do offscreen rendering via vtkOSOpenGLRenderWindow.

Is there by any chance a possibility perform onscreen and offscreen rendering with a single build of VTK 7 similar to VTK 6 and previous versions?

Best regards
Michael