WIP: Hololens 2 support using OpenXr Remoting

Based on OpenXR WIP branch added in !7907.

Goal

Add OpenXR Remoting and OpenGL-DirectX interop to the original branch to allow rendering in the Hololens 2.

This work is based on Microsoft's Holographic remoting samples. It provides the "player" client application that should be deployed in the Hololens. This branch implements the server side, similar to the "remote_openXR" sample.

Your GPU must support :

• H.265(HEVC) codec. (support matrix)
• NV_DX_Interop extension.

How to try

VTK

• Build and Install the OpenXR SDK.
• Build this branch with CMake option VTK_MODULE_ENABLE_VTK_RenderingOpenXR and set the OpenXR_LIBRARY and OpenXR_INCLUDE_DIRS CMake variable.

  ! Manual steps required when building (see TODOs to fix):

• Error: Cannot open "openxr_msft_holographic_remoting.h".. -> Install the following nuget packages in Visual Studio (Right click on RenderingOpenXR project -> Manage Nuget Packages) : Microsoft.Holographic.Remoting.OpenXr / OpenXR.Headers / OpenXR.Loader
• vtkOpenXRManager::EnableRemotingXR() uses filesystem (cpp17) to find the RemotingXR.json file -> Force cpp17 for the RenderingOpenXR project (Properties -> C / C++ -> Language -> Standard)
• The 4 .json actions file (in VTK/Rendering/OpenXR) must be placed next to the test executable/solution

Player

• Build the sample player application from Microsoft's Holographic remoting samples. ! The commit message indicates the required version of the Microsoft.Holographic.Remoting.OpenXr package.
• Deploy it to the Hololens. Send the IP address of the Hololens as first argument.

Test application

• Construct a small VTK scene as usual but using the OpenXR versions of the rendering classes:

  vtkNew<vtkOpenXRRenderer> renderer;
  renderer->SetBackground(0.0, 0.0, 0.0);
  vtkNew<vtkOpenXRRenderWindow> renderWindow;
  vtkNew<vtkOpenXRRenderWindowInteractor> iren;
  vtkNew<vtkOpenXRCamera> cam;
  renderWindow->AddRenderer(renderer);
  iren->SetRenderWindow(renderWindow);
  renderer->SetActiveCamera(cam);

  renderWindow->SetHost(argv[1]);

• Set the IP address of the Hololens using renderWindow->SetHost("XX.XX.XX.XX")

IMPORTANT: If nothing appears in the Hololens and you have both an Intel and NVidia GPU, disabling one should work.

TODOs

The last commit overrides the original WIP to show what pieces are required to add support for the Hololens 2. The following tasks must be addressed:

1. Architecture / C++

• 1.1. Clean OpenXR initial branch and refactor to use the same initialization and rendering approach as this branch.
• 1.2. Abstraction: Split OpenXR-OpenGL (initial branch) and OpenXR-DX-Remoting (this branch) implementations.
• 1.3. Don't use filesystem to construct the RemotingXR.json file path. (Use vtksys??)

2. CMake

• 2.1. Add CMake variable to build with Holographic Remoting
• 2.2. Clean Rendering/OpenGL2/CMakeLists.txt to find DirectX
• 2.3. Clean Rendering/OpenXR/CmakeLists.txt to handle .json action files correctly (or fix path in vtkOpenXRRenderWindowInteractor::LoadActions())
• 2.4. Handle finding of the 3 required Nuget packages using CMake. (Nuget package could be downloaded locally and their dir specified in CMake)

3. User experience

• 3.1. Investigate common interactions for both implementations
• 3.2. GUI: vtkQWidgetWidget ?
• 3.3. Hologram stability

4. Rendering

• 4.1. Hardware picking (requires texture flip ?)
• 4.2. Blit into OpenXR textures: OpenGL: unneeded temporary framebuffers? Remoting: Improve texture flip approach currently using Frame()