Fix pose offset on VR session start for some OpenXR runtimes

We want the session to start exactly at the landmark position, with
no additional offset. Some runtimes (e.g. Windows Mixed Reality) may
give an initial non-[0,0,0] position at session start though.

Also add a comment explaining the purpose of the eye offset variable.

1 files changed, 2 insertions, 0 deletions

diff --git a/source/blender/windowmanager/xr/intern/wm_xr_intern.h b/source/blender/windowmanager/xr/intern/wm_xr_intern.h
index 9b7b81f769a..c49e9e534b6 100644
--- a/source/blender/windowmanager/xr/intern/wm_xr_intern.h
+++ b/source/blender/windowmanager/xr/intern/wm_xr_intern.h
@@ -70,6 +70,8 @@ typedef struct wmXrDrawData {
    * space). With positional tracking enabled, it should be the same as the base pose, when
    * disabled it also contains a location delta from the moment the option was toggled. */
   GHOST_XrPose base_pose;
+  /** Offset to _substract_ from the OpenXR eye and viewer pose to get the wanted effective pose
+   * (e.g. a pose exactly at the landmark position). */
   float eye_position_ofs[3]; /* Local/view space. */
 } wmXrDrawData;