Test is also failing with VTKv6.

This crash returns when events are out of synch in changing layouts. Steve proposed a patch once before in [1] but it didn't get into VTK via gerrit. I'd like to propose patching our VTK[2] to avoid the crash and to give an error message instead, and if it works well with our nightly tests to submit it to gerrit. The vtkOpenGLRenderer is giving an error message instead of crashing so this patch matches that handling of the non active camera case.

[1] http://na-mic.org/Mantis/view.php?id=1690
[2] https://github.com/naucoin/VTK/commit/feace6d70d583ce4f861d279942b164f10c25f30

@Nicole: Sounds like a plan. Out of curiosity, I couldn't find the patch Steve submitted on Gerrit [1], do you have the link ? In parallel, I think it would make sense to re-submit to Gerrit.

[1] http://review.source.kitware.com/#/q/owner:pieper,n,z

It didn't get submitted to gerrit, just posted as a diff on the bug report.
I'll do a pull request on our VTK branch and then look at the gerrit submission process (unless Steve wants to do it - we ended up writing pretty much the same code!).

Thanks for moving forward with this.

Pull request on Slicer/VTK would be great. (make sure to base the pull request on top of "slicer-4.3-v6.1.0" [1]

[1] https://github.com/Slicer/VTK/commits/slicer-4.3-v6.1.0

The best way to get it integrated into VTK6 is to submit a patch on Gerrit. Let me know if you have any issue with this. See http://www.vtk.org/Wiki/VTK

Slicer/VTK pull request:
https://github.com/Slicer/VTK/pull/2

Partially fixed in r23462. The doesn't crash anymore but still report VTK errors. See below.

//-------------------------------------------------
BUG: Update VTKv6 external project - Fix test MarkupsInCompareViewersSelfTest

$ git shortlog 4d7abb2..169b37b
Nicole Aucoin (1):
BUG: fix null pointer crash in view to world with no active camera

This commit prevent the test from failing but it doesn't avoid the
following error from being displayed:

//------------
338: ERROR: In /home/jchris/Projects/Slicer-2-SuperBuild-Debug/VTKv6/Rendering/Core/vtkRenderer.cxx, line 1252
338: vtkOpenGLRenderer (0x741a1d0): ViewToWorld: no active camera, cannot compute view to world, returning 0,0,0
338:
338:
338: MH Head in background, scrolled to a fiducial
[...]
338: Switched back to conventional layout
338: Switched to Compare grid
338: ERROR: In /home/jchris/Projects/Slicer-2-SuperBuild-Debug/VTKv6/Common/ExecutionModel/vtkAlgorithm.cxx, line 1421
338: vtkOpenGLImageMapper (0x7548770): Attempt to get connection index 0 for input port 0, which has 0 connections.
//------------

See 0003761

svn 23493 [1] checks for active cameras before repositioning or enabling the fiducial widget or handles. The test is no longer printing error messages and the updates get called again to update once the renderer has been set up properly.

[1] http://viewvc.slicer.org/viewvc.cgi/Slicer4?view=revision&revision=23493