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, 81 insertions, 0 deletions

diff --git a/source/blender/windowmanager/intern/wm_operators.c b/source/blender/windowmanager/intern/wm_operators.c
index d649b21569e..1d6ae10c396 100644
--- a/source/blender/windowmanager/intern/wm_operators.c
+++ b/source/blender/windowmanager/intern/wm_operators.c
@@ -3645,6 +3645,84 @@ static void WM_OT_stereo3d_set(wmOperatorType *ot)
 
 /** \} */
 
+#ifdef WITH_XR_OPENXR
+
+static void wm_xr_session_update_screen(Main *bmain, const wmXrData *xr_data)
+{
+  const bool session_exists = WM_xr_session_exists(xr_data);
+
+  for (bScreen *screen = bmain->screens.first; screen; screen = screen->id.next) {
+    for (ScrArea *area = screen->areabase.first; area; area = area->next) {
+      for (SpaceLink *slink = area->spacedata.first; slink; slink = slink->next) {
+        if (slink->spacetype == SPACE_VIEW3D) {
+          View3D *v3d = (View3D *)slink;
+
+          if (v3d->flag & V3D_XR_SESSION_MIRROR) {
+            ED_view3d_xr_mirror_update(area, v3d, session_exists);
+          }
+
+          if (session_exists) {
+            wmWindowManager *wm = bmain->wm.first;
+            const Scene *scene = WM_windows_scene_get_from_screen(wm, screen);
+
+            ED_view3d_xr_shading_update(wm, v3d, scene);
+          }
+          /* Ensure no 3D View is tagged as session root. */
+          else {
+            v3d->runtime.flag &= ~V3D_RUNTIME_XR_SESSION_ROOT;
+          }
+        }
+      }
+    }
+  }
+}
+
+static void wm_xr_session_update_screen_on_exit_cb(const wmXrData *xr_data)
+{
+  /* Just use G_MAIN here, storing main isn't reliable enough on file read or exit. */
+  wm_xr_session_update_screen(G_MAIN, xr_data);
+}
+
+static int wm_xr_session_toggle_exec(bContext *C, wmOperator *UNUSED(op))
+{
+  Main *bmain = CTX_data_main(C);
+  wmWindowManager *wm = CTX_wm_manager(C);
+  View3D *v3d = CTX_wm_view3d(C);
+
+  /* Lazy-create xr context - tries to dynlink to the runtime, reading active_runtime.json. */
+  if (wm_xr_init(wm) == false) {
+    return OPERATOR_CANCELLED;
+  }
+
+  v3d->runtime.flag |= V3D_RUNTIME_XR_SESSION_ROOT;
+  wm_xr_session_toggle(wm, wm_xr_session_update_screen_on_exit_cb);
+  wm_xr_session_update_screen(bmain, &wm->xr);
+
+  WM_event_add_notifier(C, NC_WM | ND_XR_DATA_CHANGED, NULL);
+
+  return OPERATOR_FINISHED;
+}
+
+static void WM_OT_xr_session_toggle(wmOperatorType *ot)
+{
+  /* identifiers */
+  ot->name = "Toggle VR Session";
+  ot->idname = "WM_OT_xr_session_toggle";
+  ot->description =
+      "Open a view for use with virtual reality headsets, or close it if already "
+      "opened";
+
+  /* callbacks */
+  ot->exec = wm_xr_session_toggle_exec;
+  ot->poll = ED_operator_view3d_active;
+
+  /* XXX INTERNAL just to hide it from the search menu by default, an Add-on will expose it in the
+   * UI instead. Not meant as a permanent solution. */
+  ot->flag = OPTYPE_INTERNAL;
+}
+
+#endif /* WITH_XR_OPENXR */
+
 /* -------------------------------------------------------------------- */
 /** \name Operator Registration & Keymaps
  * \{ */
@@ -3686,6 +3764,9 @@ void wm_operatortypes_register(void)
   WM_operatortype_append(WM_OT_call_panel);
   WM_operatortype_append(WM_OT_radial_control);
   WM_operatortype_append(WM_OT_stereo3d_set);
+#ifdef WITH_XR_OPENXR
+  WM_operatortype_append(WM_OT_xr_session_toggle);
+#endif
 #if defined(WIN32)
   WM_operatortype_append(WM_OT_console_toggle);
 #endif