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, 118 insertions, 0 deletions

diff --git a/source/blender/windowmanager/intern/wm_surface.c b/source/blender/windowmanager/intern/wm_surface.c
new file mode 100644
index 00000000000..cb575cc8f7d
--- /dev/null
+++ b/source/blender/windowmanager/intern/wm_surface.c
@@ -0,0 +1,118 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+/** \file
+ * \ingroup wm
+ */
+
+#include "BKE_context.h"
+
+#include "BLF_api.h"
+
+#include "BLI_listbase.h"
+#include "BLI_threads.h"
+
+#include "GHOST_C-api.h"
+
+#include "GPU_batch_presets.h"
+#include "GPU_framebuffer.h"
+#include "GPU_immediate.h"
+#include "GPU_context.h"
+
+#include "MEM_guardedalloc.h"
+
+#include "WM_types.h"
+#include "WM_api.h"
+#include "wm.h"
+
+#include "wm_surface.h"
+
+static ListBase global_surface_list = {NULL, NULL};
+static wmSurface *g_drawable = NULL;
+
+void wm_surfaces_iter(bContext *C, void (*cb)(bContext *C, wmSurface *))
+{
+  for (wmSurface *surf = global_surface_list.first; surf; surf = surf->next) {
+    cb(C, surf);
+  }
+}
+
+void wm_surface_clear_drawable(void)
+{
+  if (g_drawable) {
+    BLF_batch_reset();
+    gpu_batch_presets_reset();
+    immDeactivate();
+
+    g_drawable = NULL;
+  }
+}
+
+void wm_surface_set_drawable(wmSurface *surface, bool activate)
+{
+  BLI_assert(ELEM(g_drawable, NULL, surface));
+
+  g_drawable = surface;
+  if (activate) {
+    GHOST_ActivateOpenGLContext(surface->ghost_ctx);
+  }
+
+  GPU_context_active_set(surface->gpu_ctx);
+  immActivate();
+}
+
+void wm_surface_make_drawable(wmSurface *surface)
+{
+  BLI_assert(GPU_framebuffer_active_get() == NULL);
+
+  if (surface != g_drawable) {
+    wm_surface_clear_drawable();
+    wm_surface_set_drawable(surface, true);
+  }
+}
+
+void wm_surface_reset_drawable(void)
+{
+  BLI_assert(BLI_thread_is_main());
+  BLI_assert(GPU_framebuffer_active_get() == NULL);
+
+  if (g_drawable) {
+    wm_surface_clear_drawable();
+    wm_surface_set_drawable(g_drawable, true);
+  }
+}
+
+void wm_surface_add(wmSurface *surface)
+{
+  BLI_addtail(&global_surface_list, surface);
+}
+
+void wm_surface_remove(wmSurface *surface)
+{
+  BLI_remlink(&global_surface_list, surface);
+  surface->free_data(surface);
+  MEM_freeN(surface);
+}
+
+void wm_surfaces_free(void)
+{
+  for (wmSurface *surf = global_surface_list.first, *surf_next; surf; surf = surf_next) {
+    surf_next = surf->next;
+    wm_surface_remove(surf);
+  }
+
+  BLI_assert(BLI_listbase_is_empty(&global_surface_list));
+}