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, 20 insertions, 11 deletions

diff --git a/intern/ghost/GHOST_Types.h b/intern/ghost/GHOST_Types.h
index adda782b96d..70c4d3ef00c 100644
--- a/intern/ghost/GHOST_Types.h
+++ b/intern/ghost/GHOST_Types.h
@@ -598,6 +598,8 @@ typedef void (*GHOST_TimerProcPtr)(struct GHOST_TimerTaskHandle__ *task, GHOST_T
 
 #ifdef WITH_XR_OPENXR
 
+struct GHOST_XrError;
+struct GHOST_XrDrawViewInfo;
 /**
  * The XR view (i.e. the OpenXR runtime) may require a different graphics library than OpenGL. An
  * offscreen texture of the viewport will then be drawn into using OpenGL, but the final texture
@@ -605,7 +607,7 @@ typedef void (*GHOST_TimerProcPtr)(struct GHOST_TimerTaskHandle__ *task, GHOST_T
  *
  * This enum defines the possible graphics bindings to attempt to enable.
  */
-typedef enum {
+typedef enum GHOST_TXrGraphicsBinding {
   GHOST_kXrGraphicsUnknown = 0,
   GHOST_kXrGraphicsOpenGL,
 #  ifdef WIN32
@@ -614,6 +616,16 @@ typedef enum {
   /* For later */
   //  GHOST_kXrGraphicsVulkan,
 } GHOST_TXrGraphicsBinding;
+
+typedef void (*GHOST_XrErrorHandlerFn)(const struct GHOST_XrError *);
+
+typedef void (*GHOST_XrSessionExitFn)(void *customdata);
+
+typedef void *(*GHOST_XrGraphicsContextBindFn)(enum GHOST_TXrGraphicsBinding graphics_lib);
+typedef void (*GHOST_XrGraphicsContextUnbindFn)(enum GHOST_TXrGraphicsBinding graphics_lib,
+                                                GHOST_ContextHandle graphics_context);
+typedef void (*GHOST_XrDrawViewFn)(const struct GHOST_XrDrawViewInfo *draw_view, void *customdata);
+
 /* An array of GHOST_TXrGraphicsBinding items defining the candidate bindings to use. The first
  * available candidate will be chosen, so order defines priority. */
 typedef const GHOST_TXrGraphicsBinding *GHOST_XrGraphicsBindingCandidates;
@@ -638,13 +650,17 @@ typedef struct {
 
 typedef struct {
   GHOST_XrPose base_pose;
+
+  GHOST_XrSessionExitFn exit_fn;
+  void *exit_customdata;
 } GHOST_XrSessionBeginInfo;
 
-typedef struct {
+typedef struct GHOST_XrDrawViewInfo {
   int ofsx, ofsy;
   int width, height;
 
-  GHOST_XrPose pose;
+  GHOST_XrPose eye_pose;
+  GHOST_XrPose local_pose;
 
   struct {
     float angle_left, angle_right;
@@ -655,19 +671,12 @@ typedef struct {
   char expects_srgb_buffer;
 } GHOST_XrDrawViewInfo;
 
-typedef struct {
+typedef struct GHOST_XrError {
   const char *user_message;
 
   void *customdata;
 } GHOST_XrError;
 
-typedef void (*GHOST_XrErrorHandlerFn)(const GHOST_XrError *);
-
-typedef void *(*GHOST_XrGraphicsContextBindFn)(GHOST_TXrGraphicsBinding graphics_lib);
-typedef void (*GHOST_XrGraphicsContextUnbindFn)(GHOST_TXrGraphicsBinding graphics_lib,
-                                                void *graphics_context);
-typedef void (*GHOST_XrDrawViewFn)(const GHOST_XrDrawViewInfo *draw_view, void *customdata);
-
 #endif
 
 #endif  // __GHOST_TYPES_H__