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

3 files changed, 59 insertions, 0 deletions

diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index c3fba697bd3..f1f274f97d5 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -7187,6 +7187,7 @@ static void direct_link_region(FileData *fd, ARegion *region, int spacetype)
         rv3d->smooth_timer = NULL;
 
         rv3d->rflag &= ~(RV3D_NAVIGATING | RV3D_PAINTING);
+        rv3d->runtime_viewlock = 0;
       }
     }
   }
@@ -7277,7 +7278,10 @@ static void direct_link_area(FileData *fd, ScrArea *area)
         direct_link_gpencil(fd, v3d->gpd);
       }
       v3d->localvd = newdataadr(fd, v3d->localvd);
+
+      /* Runtime data */
       v3d->runtime.properties_storage = NULL;
+      v3d->runtime.flag = 0;
 
       /* render can be quite heavy, set to solid on load */
       if (v3d->shading.type == OB_RENDER) {
@@ -7658,6 +7662,23 @@ static bool direct_link_area_map(FileData *fd, ScrAreaMap *area_map)
 /** \} */
 
 /* -------------------------------------------------------------------- */
+/** \name XR-data
+ * \{ */
+
+static void direct_link_wm_xr_data(FileData *fd, wmXrData *xr_data)
+{
+  direct_link_view3dshading(fd, &xr_data->session_settings.shading);
+}
+
+static void lib_link_wm_xr_data(FileData *fd, ID *parent_id, wmXrData *xr_data)
+{
+  xr_data->session_settings.base_pose_object = newlibadr(
+      fd, parent_id->lib, xr_data->session_settings.base_pose_object);
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
 /** \name Read ID: Window Manager
  * \{ */
 
@@ -7710,6 +7731,8 @@ static void direct_link_windowmanager(FileData *fd, wmWindowManager *wm)
     }
   }
 
+  direct_link_wm_xr_data(fd, &wm->xr);
+
   BLI_listbase_clear(&wm->timers);
   BLI_listbase_clear(&wm->operators);
   BLI_listbase_clear(&wm->paintcursors);
@@ -7724,6 +7747,8 @@ static void direct_link_windowmanager(FileData *fd, wmWindowManager *wm)
 
   wm->message_bus = NULL;
 
+  wm->xr.runtime = NULL;
+
   BLI_listbase_clear(&wm->jobs);
   BLI_listbase_clear(&wm->drags);
 
@@ -7747,6 +7772,8 @@ static void lib_link_windowmanager(FileData *fd, Main *UNUSED(bmain), wmWindowMa
     for (ScrArea *area = win->global_areas.areabase.first; area; area = area->next) {
       lib_link_area(fd, &wm->id, area);
     }
+
+    lib_link_wm_xr_data(fd, &wm->id, &wm->xr);
   }
 }
 
@@ -7911,6 +7938,12 @@ static void lib_link_main_data_restore(struct IDNameLib_Map *id_map, Main *newma
   FOREACH_MAIN_ID_END;
 }
 
+static void lib_link_wm_xr_data_restore(struct IDNameLib_Map *id_map, wmXrData *xr_data)
+{
+  xr_data->session_settings.base_pose_object = restore_pointer_by_name(
+      id_map, (ID *)xr_data->session_settings.base_pose_object, USER_REAL);
+}
+
 static void lib_link_window_scene_data_restore(wmWindow *win, Scene *scene, ViewLayer *view_layer)
 {
   bScreen *screen = BKE_workspace_active_screen_get(win->workspace_hook);
@@ -8241,6 +8274,8 @@ void blo_lib_link_restore(Main *oldmain,
     BLI_assert(win->screen == NULL);
   }
 
+  lib_link_wm_xr_data_restore(id_map, &curwm->xr);
+
   /* Restore all ID pointers in Main database itself
    * (especially IDProperties might point to some word-space of other 'weirdly unchanged' ID
    * pointers, see T69146).
diff --git a/source/blender/blenloader/intern/versioning_280.c b/source/blender/blenloader/intern/versioning_280.c
index 87442a10d12..3535897aa66 100644
--- a/source/blender/blenloader/intern/versioning_280.c
+++ b/source/blender/blenloader/intern/versioning_280.c
@@ -30,6 +30,8 @@
 #include "BLI_string.h"
 #include "BLI_utildefines.h"
 
+#include "DNA_defaults.h"
+
 #include "DNA_anim_types.h"
 #include "DNA_object_types.h"
 #include "DNA_camera_types.h"
@@ -4845,5 +4847,21 @@ void blo_do_versions_280(FileData *fd, Library *UNUSED(lib), Main *bmain)
         }
       }
     }
+
+    if (!DNA_struct_find(fd->filesdna, "XrSessionSettings")) {
+      for (wmWindowManager *wm = bmain->wm.first; wm; wm = wm->id.next) {
+        const View3D *v3d_default = DNA_struct_default_get(View3D);
+
+        wm->xr.session_settings.shading = v3d_default->shading;
+        /* Don't rotate light with the viewer by default, make it fixed. */
+        wm->xr.session_settings.shading.flag |= V3D_SHADING_WORLD_ORIENTATION;
+        wm->xr.session_settings.draw_flags = (V3D_OFSDRAW_SHOW_GRIDFLOOR |
+                                              V3D_OFSDRAW_SHOW_ANNOTATION);
+        wm->xr.session_settings.clip_start = v3d_default->clip_start;
+        wm->xr.session_settings.clip_end = v3d_default->clip_end;
+
+        wm->xr.session_settings.flag = XR_SESSION_USE_POSITION_TRACKING;
+      }
+    }
   }
 }
diff --git a/source/blender/blenloader/intern/writefile.c b/source/blender/blenloader/intern/writefile.c
index 29366e3bae5..837134c0156 100644
--- a/source/blender/blenloader/intern/writefile.c
+++ b/source/blender/blenloader/intern/writefile.c
@@ -2820,6 +2820,11 @@ static void write_gpencil(WriteData *wd, bGPdata *gpd)
   }
 }
 
+static void write_wm_xr_data(WriteData *wd, wmXrData *xr_data)
+{
+  write_view3dshading(wd, &xr_data->session_settings.shading);
+}
+
 static void write_region(WriteData *wd, ARegion *region, int spacetype)
 {
   writestruct(wd, DATA, ARegion, 1, region);
@@ -3066,6 +3071,7 @@ static void write_windowmanager(WriteData *wd, wmWindowManager *wm)
 {
   writestruct(wd, ID_WM, wmWindowManager, 1, wm);
   write_iddata(wd, &wm->id);
+  write_wm_xr_data(wd, &wm->xr);
 
   for (wmWindow *win = wm->windows.first; win; win = win->next) {
 #ifndef WITH_GLOBAL_AREA_WRITING