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

1 files changed, 28 insertions, 5 deletions

diff --git a/source/blender/makesdna/DNA_view3d_types.h b/source/blender/makesdna/DNA_view3d_types.h
index a25d66cbc9b..3dc29d40bc1 100644
--- a/source/blender/makesdna/DNA_view3d_types.h
+++ b/source/blender/makesdna/DNA_view3d_types.h
@@ -106,10 +106,12 @@ typedef struct RegionView3D {
   char persp;
   char view;
   char view_axis_roll;
-  char viewlock;
+  char viewlock; /* Should usually be accessed with RV3D_LOCK_FLAGS()! */
+  /** Options for runtime only locking (cleared on file read) */
+  char runtime_viewlock; /* Should usually be accessed with RV3D_LOCK_FLAGS()! */
   /** Options for quadview (store while out of quad view). */
   char viewlock_quad;
-  char _pad[2];
+  char _pad[1];
   /** Normalized offset for locked view: (-1, -1) bottom left, (1, 1) upper right. */
   float ofs_lock[2];
 
@@ -232,6 +234,10 @@ typedef struct View3DOverlay {
 typedef struct View3D_Runtime {
   /** Nkey panel stores stuff here. */
   void *properties_storage;
+  /** Runtime only flags. */
+  int flag;
+
+  char _pad1[4];
 } View3D_Runtime;
 
 /** 3D ViewPort Struct. */
@@ -342,6 +348,7 @@ typedef struct View3D {
 #define V3D_FLAG_UNUSED_1 (1 << 1) /* cleared */
 #define V3D_HIDE_HELPLINES (1 << 2)
 #define V3D_INVALID_BACKBUF (1 << 3)
+#define V3D_XR_SESSION_MIRROR (1 << 4)
 
 #define V3D_FLAG_UNUSED_10 (1 << 10) /* cleared */
 #define V3D_SELECT_OUTLINE (1 << 11)
@@ -349,6 +356,12 @@ typedef struct View3D {
 #define V3D_GLOBAL_STATS (1 << 13)
 #define V3D_DRAW_CENTERS (1 << 15)
 
+/** #View3D_Runtime.flag */
+enum {
+  /** The 3D view which the XR session was created in is flagged with this. */
+  V3D_RUNTIME_XR_SESSION_ROOT = (1 << 0),
+};
+
 /** #RegionView3D.persp */
 #define RV3D_ORTHO 0
 #define RV3D_PERSP 1
@@ -367,9 +380,19 @@ typedef struct View3D {
 #define RV3D_ZOFFSET_DISABLED 64
 
 /** #RegionView3D.viewlock */
-#define RV3D_LOCKED (1 << 0)
-#define RV3D_BOXVIEW (1 << 1)
-#define RV3D_BOXCLIP (1 << 2)
+enum {
+  RV3D_LOCK_ROTATION = (1 << 0),
+  RV3D_BOXVIEW = (1 << 1),
+  RV3D_BOXCLIP = (1 << 2),
+  RV3D_LOCK_LOCATION = (1 << 3),
+  RV3D_LOCK_ZOOM_AND_DOLLY = (1 << 4),
+
+  RV3D_LOCK_ANY_TRANSFORM = (RV3D_LOCK_LOCATION | RV3D_LOCK_ROTATION | RV3D_LOCK_ZOOM_AND_DOLLY),
+};
+
+/* Bitwise OR of the regular lock-flags with runtime only lock-flags. */
+#define RV3D_LOCK_FLAGS(rv3d) ((rv3d)->viewlock | ((rv3d)->runtime_viewlock))
+
 /** #RegionView3D.viewlock_quad */
 #define RV3D_VIEWLOCK_INIT (1 << 7)