VTK includes built-in support for developing VR applications. The support works with HTC Vive, Oculus Rift, and various Windows Mixed Reality headsets. It leverages the OpenVR standard, so it is easy to use, if you are familiar with VTK.

To start using VTK in VR, first download and install the OpenVR SDK. Also check that you are set up to use a recent version of VTK, as older versions may not work with current device drivers. Once you configure VTK and turn on the modules you desire, you can begin the build process. To maximize performance, try building an optimized version of the software platform.

As for existing applications, most can leverage VTK’s VR support with minimal changes to their codebase. Just link your executable to the vtkRenderingOpenVR module, and change four classes (renderWindow, renderer, interactor, and camera) to specifically create them as OpenVR. All other classes, such as actors and mappers, can remain unchanged.

A typical VTK program, for example, may have the following:

  vtkNew<vtkRenderWindow> renderWindow;
  vtkNew<vtkRenderer> renderer;
  renderWindow->AddRenderer(renderer);
  vtkNew<vtkRenderWindowInteractor> iren;
  iren->SetRenderWindow(renderWindow);
  vtkNew<vtkCamera> cam;
  renderer->SetActiveCamera(cam);

To use OpenVR, just modify the above to this:

  vtkNew<vtkOpenVRRenderWindow> renderWindow;
  vtkNew<vtkOpenVRRenderer> renderer;
  renderWindow->AddRenderer(renderer);
  vtkNew<vtkOpenVRRenderWindowInteractor> iren;
  iren->SetRenderWindow(renderWindow);
  vtkNew<vtkOpenVRCamera> cam;
  renderer->SetActiveCamera(cam);

Two classes, vtkOpenVRRenderWindow and vtkOpenVRRenderWindowInteractor, deserve some additional comments.

vtkOpenVRRenderWindow
The vtkOpenVRRenderWindow class handles the bulk of the interaction with OpenVR. It currently supports one renderer that covers the entire window. It also holds the transformation from physical space (e.g., a room) to world coordinates for your visualization. Four methods perform the mapping: SetPhysicalScale, SetPhysicalTranslation, SetPhysicalViewUp, and SetPhysicalViewDirection.

Physical space is measured in meters, and the origin is located on the floor in the middle of the room. If the world coordinates are measured in light years, for example, you can use PhysicalScale to scale them down to a suitable size for the room. The convenience method ResetCamera() on vtkOpenVRRenderer is responsible for computing a reasonable value for PhysicalScale and PhysicalTranslation.

vtkOpenVRRenderWindowInteractor
While VTK is designed to pick and interact based on X,Y mouse/window coordinates, OpenVR provides six-degrees-of-freedom events that contain X,Y,Z world coordinates and W,X,Y,Z orientations. The vtkOpenVRRenderWindowInteractor class handles these VR controller events and forwards them to the widgets in VTK.

Applications

VTK’s support for VR is employed by applications such as ParaView. ParaView is Kitware’s scientific visualization application. It has an OpenVR plugin that allows you to send a visualization to VR for immersive viewing. For Windows, ParaView binaries come with the plugin prebuilt.

3D Slicer is another application that employs VTK’s support for VR. 3D Slicer visualizes medical datasets for training and surgical planning. It can simulate bilateral sagittal split osteotomy, visualize anatomy, and help doctors prepare for biopsies.

As VR hardware and software continue to change, Kitware is happy to help you leverage VR in new application domains through support, custom development, unique capabilities, and future research programs. For more information, please contact Kitware.