Documentation/Labs/VTK8

This page documents the update of Slicer to use VTK 8.0.

Overview

It is planned to update the version of VTK that Slicer uses from 7.1 to 8.0.

Status

• Builds on Linux and Windows; Mac is untested. Test runs are in progress.
• EMSegment remote module will require updates to fix vtkDebugLeaks output.
• Running on Windows gives OpenGL errors at exit with the OpenGL backend. The OpenGL2 backend is untested.
• "VTKv7" project name needs to be updated to "VTKv8".

Branches/Merge Requests

VTK:

• https://github.com/Slicer/VTK/commits/slicer-v8.0.0-2017-06-26-782d7ed

Slicer:

• https://github.com/msmolens/Slicer/commits/support-vtk8

Outstanding VTK issues

• Should upstream fix to respect access specifier of using statements in wrapping
  • https://github.com/Slicer/VTK/commit/0b57aba27dfeca72227ff417e4254aaad8ccb367

Slicer-specific VTK commits

Slicer's VTK 8.0 branch includes fixes/changes that aren't in upstream:

• Respect access specifier of using statements in wrapping
  • https://github.com/Slicer/VTK/commit/93a7c677481259cf23121a053d82ba4b7c2286e6
• ENH: Allow selection of seed points using vtkSeedWidget
  • https://github.com/Slicer/VTK/commit/734709ee38a0a25c92a9a0c7477cfddec5e12cf3
• Ensure vtkVariant stream associated with << operator is set back to "dec".
  • https://github.com/Slicer/VTK/commit/dbf5de60c0809ca6233fe428761ef19e561ef542
• BUG: WIP: fix vtkPickingManager interaction with widgets
  • https://github.com/Slicer/VTK/commit/2c55e994475b6568a5b3e7363ab70c4dd722cc5d

Tests

This section lists test failures on each platform for Release builds.

Windows:

Test results:

• TBD

Linux:

Test results:

• TBD

OS X:

Test results:

• TBD

Rendering backend

Although VTK 7 changed the default setting of VTK_RENDERING_BACKEND to OpenGL2, Slicer still explicitly sets it to OpenGL. Using the OpenGL2 backend in Slicer is untested and may require updates to properly build and function. This rendering backend in Slicer is set using Slicer_VTK_RENDERING_BACKEND.

OpenGL2 backend known issues

Open

• Need to move OS X nightly build to new factory machine to be able to set CMAKE_OSX_DEPLOYMENT_TARGET:STRING=10.7. This will ensure that the required OpenGL version is found. See https://github.com/Slicer/Slicer/pull/595.
• 4252: Slicer crashes on start when started through Windows Remote Desktop

Discussion

The transition plan was announced on the Slicer forum: https://discourse.slicer.org/t/transition-to-vtk-8-0/379.

Migration guide

This section lists categories of code changes necessary to build and run Slicer with VTK 8.0. Each category has a short description, an example error message, a suggested upgrade path, and references to relevant commits.

Use hierarchy files for VTK Python wrapping

In VTK8 it's necessary to generate hierarchy files for proper wrapping VTK classes in Python. Without the information provided by the hierarchy files, the Python wrapping tool lacks complete information about classes and types. In this case, the generated classes contain methods that shouldn't be wrapped and fail to compile, and include references to types such as vtkTypeBool. Once the hierarchy files are generated and provided to the Python wrapping tool, the generated classes compile and typedefs like vtkTypeBool are correctly resolved.

Once the VTK8 changes are merged, generating hierarchy files is handled by https://github.com/Slicer/Slicer/blob/master/CMake/vtkMacroKitPythonWrap.cmake.

References:

• http://www.vtk.org/Wiki/VTK/WrapHierarchy

Call InitializeObjectBase() in vtkObject New() methods

In VTK8 it's necessary for vtkObject New() methods to call InitializeObjectBase() on the new object for proper tracking with vtkDebugLeaks. The standard macros (vtkStandardNewMacro, vtkObjectFactoryNewMacro) handle this. For those classes that don't use the macros, add a call to InitializeObjectBase() immediately after constructing the object by new vtkXXX().

Additionally, vtkObjectFactory::CreateInstance() now doesn't register the class name with vtkDebugLeaks if the factory fails to create the object. Therefore, it's no longer necessary to unregister the class name with vtkDebugLeaks. Remove calls to vtkDebugLeaks::DestructClass(className) following vtkObjectFactory::CreateInstance().

To support both VTK8 and earlier versions of VTK, wrap these changes in preprocessor checks for whether VTK_HAS_INITIALIZE_OBJECT_BASE is defined.

References:

• https://github.com/Kitware/VTK/commit/e5c793dbdf87e838bb2b60c6a5905ced0e5548f9
• http://public.kitware.com/pipermail/vtk-developers/2016-September/034332.html

Future work

Future work in Slicer related to VTK 8 could include:

• Remove BTX/ETX markers.
• CHeck for and resolve build warnings in Slicer VTK classes.
• Check that settings in External_VTKv8.cmake are all still necessary, specifically VTK_USE_PARALLEL, and anything related to Qt.