VR: Initial Virtual Reality support - Milestone 1, Scene Inspection

NOTE: While most of the milestone 1 goals are there, a few smaller features and
improvements are still to be done.

Big picture of this milestone: Initial, OpenXR-based virtual reality support
for users and foundation for advanced use cases.
Maniphest Task: https://developer.blender.org/T71347
The tasks contains more information about this milestone.

To be clear: This is not a feature rich VR implementation, it's focused on the
initial scene inspection use case. We intentionally focused on that, further
features like controller support are part of the next milestone.

- How to use?
Instructions on how to use this are here:
https://wiki.blender.org/wiki/User:Severin/GSoC-2019/How_to_Test
These will be updated and moved to a more official place (likely the manual) soon.

Currently Windows Mixed Reality and Oculus devices are usable. Valve/HTC
headsets don't support the OpenXR standard yet and hence, do not work with this
implementation.

---------------

This is the C-side implementation of the features added for initial VR
support as per milestone 1. A "VR Scene Inspection" Add-on will be
committed separately, to expose the VR functionality in the UI. It also
adds some further features for milestone 1, namely a landmarking system
(stored view locations in the VR space)

Main additions/features:
* Support for rendering viewports to an HMD, with good performance.
* Option to sync the VR view perspective with a fully interactive,
  regular 3D View (VR-Mirror).
* Option to disable positional tracking. Keeps the current position (calculated
  based on the VR eye center pose) when enabled while a VR session is running.
* Some regular viewport settings for the VR view
* RNA/Python-API to query and set VR session state information.
* WM-XR: Layer tying Ghost-XR to the Blender specific APIs/data
* wmSurface API: drawable, non-window container (manages Ghost-OpenGL and GPU
  context)
* DNA/RNA for management of VR session settings
* `--debug-xr` and `--debug-xr-time` commandline options
* Utility batch & config file for using the Oculus runtime on Windows.
* Most VR data is runtime only. The exception is user settings which are saved
  to files (`XrSessionSettings`).
* VR support can be disabled through the `WITH_XR_OPENXR` compiler flag.

For architecture and code documentation, see
https://wiki.blender.org/wiki/Source/Interface/XR.

---------------

A few thank you's:
* A huge shoutout to Ray Molenkamp for his help during the project - it would
  have not been that successful without him!
* Sebastian Koenig and Simeon Conzendorf for testing and feedback!
* The reviewers, especially Brecht Van Lommel!
* Dalai Felinto for pushing and managing me to get this done ;)
* The OpenXR working group for providing an open standard. I think we're the
  first bigger application to adopt OpenXR. Congratulations to them and
  ourselves :)

This project started as a Google Summer of Code 2019 project - "Core Support of
Virtual Reality Headsets through OpenXR" (see
https://wiki.blender.org/wiki/User:Severin/GSoC-2019/).
Some further information, including ideas for further improvements can be found
in the final GSoC report:
https://wiki.blender.org/wiki/User:Severin/GSoC-2019/Final_Report

Differential Revisions: D6193, D7098

Reviewed by: Brecht Van Lommel, Jeroen Bakker

2 files changed, 23 insertions, 0 deletions

diff --git a/release/windows/batch/blender_oculus.cmd b/release/windows/batch/blender_oculus.cmd
new file mode 100644
index 00000000000..ffb725eb32f
--- /dev/null
+++ b/release/windows/batch/blender_oculus.cmd
@@ -0,0 +1,14 @@
+@echo off
+
+REM Helper setting hints to get the OpenXR preview support enabled for Oculus.
+REM Of course this is not meant as a permanent solution. Oculus will likely provide a better setup at some point.
+
+echo Starting Blender with Oculus OpenXR support. This assumes the Oculus runtime
+echo is installed in the default location. If this is not the case, please adjust
+echo the path inside oculus.json.
+echo.
+echo Note that OpenXR support in Oculus is considered a preview. Use with care!
+echo.
+pause
+set XR_RUNTIME_JSON=%~dp0oculus.json
+blender
diff --git a/release/windows/batch/oculus.json b/release/windows/batch/oculus.json
new file mode 100644
index 00000000000..ba8767f2c58
--- /dev/null
+++ b/release/windows/batch/oculus.json
@@ -0,0 +1,9 @@
+{
+    "file_format_version": "1.0.0",
+    "runtime":
+    {
+        "api_version": "1.0",
+        "name": "Oculus OpenXR",
+        "library_path": "c:\\Program Files\\Oculus\\Support\\oculus-runtime\\LibOVRRT64_1.dll"
+    }
+}