XR: Expose the OpenXR user paths in the event data for XR events

The use-case is to allow an event handler (in C or a plugin) to
distinguish which hand produced the XR event.

The alternative is to register separate actions for each hand (e.g.
"trigger_left" and "trigger_right"), and duplicate the device bindings
(Oculus, HTC Vive, etc) for each action. Other than the problem of code
duplication, this isn't conceptually efficient since "trigger_left" and
"trigger_right" both represent the same event "trigger", and the
identity of the hand that produced that event is just a property of
that event.

Adds two string fields to the XrEventData called user_path and
user_path_other. The user_path_other field will be populated if the
event is a bimanual one (i.e. two-handed). This follows the pattern
used by the rest of the XrEventData struct for bimanual events (e.g.
state, state_other).

Reviewed By: muxed-reality

source/blender/makesrna/intern/rna_xr.c

@@ -1196,6 +1196,50 @@ static int rna_XrEventData_action_length(PointerRNA *ptr)
 #  endif
 }
 
+static void rna_XrEventData_user_path_get(PointerRNA *ptr, char *r_value)
+{
+#  ifdef WITH_XR_OPENXR
+  const wmXrActionData *data = ptr->data;
+  strcpy(r_value, data->user_path);
+#  else
+  UNUSED_VARS(ptr);
+  r_value[0] = '\0';
+#  endif
+}
+
+static int rna_XrEventData_user_path_length(PointerRNA *ptr)
+{
+#  ifdef WITH_XR_OPENXR
+  const wmXrActionData *data = ptr->data;
+  return strlen(data->user_path);
+#  else
+  UNUSED_VARS(ptr);
+  return 0;
+#  endif
+}
+
+static void rna_XrEventData_user_path_other_get(PointerRNA *ptr, char *r_value)
+{
+#  ifdef WITH_XR_OPENXR
+  const wmXrActionData *data = ptr->data;
+  strcpy(r_value, data->user_path_other);
+#  else
+  UNUSED_VARS(ptr);
+  r_value[0] = '\0';
+#  endif
+}
+
+static int rna_XrEventData_user_path_other_length(PointerRNA *ptr)
+{
+#  ifdef WITH_XR_OPENXR
+  const wmXrActionData *data = ptr->data;
+  return strlen(data->user_path_other);
+#  else
+  UNUSED_VARS(ptr);
+  return 0;
+#  endif
+}
+
 static int rna_XrEventData_type_get(PointerRNA *ptr)
 {
 #  ifdef WITH_XR_OPENXR
@@ -2402,6 +2446,19 @@ static void rna_def_xr_eventdata(BlenderRNA *brna)
       prop, "rna_XrEventData_action_get", "rna_XrEventData_action_length", NULL);
   RNA_def_property_ui_text(prop, "Action", "XR action name");
 
+  prop = RNA_def_property(srna, "user_path", PROP_STRING, PROP_NONE);
+  RNA_def_property_clear_flag(prop, PROP_EDITABLE);
+  RNA_def_property_string_funcs(
+      prop, "rna_XrEventData_user_path_get", "rna_XrEventData_user_path_length", NULL);
+  RNA_def_property_ui_text(prop, "User Path", "User path of the action. E.g. \"/user/hand/left\"");
+
+  prop = RNA_def_property(srna, "user_path_other", PROP_STRING, PROP_NONE);
+  RNA_def_property_clear_flag(prop, PROP_EDITABLE);
+  RNA_def_property_string_funcs(
+      prop, "rna_XrEventData_user_path_other_get", "rna_XrEventData_user_path_other_length", NULL);
+  RNA_def_property_ui_text(
+      prop, "User Path Other", "Other user path, for bimanual actions. E.g. \"/user/hand/right\"");
+
   prop = RNA_def_property(srna, "type", PROP_ENUM, PROP_NONE);
   RNA_def_property_clear_flag(prop, PROP_EDITABLE);
   RNA_def_property_enum_items(prop, rna_enum_xr_action_types);

source/blender/windowmanager/WM_types.h

@@ -812,6 +812,10 @@ typedef struct wmXrActionData {
   char action_set[64];
   /** Action name. */
   char action[64];
+  /** User path. E.g. "/user/hand/left" */
+  char user_path[64];
+  /** Other user path, for bimanual actions. E.g. "/user/hand/right" */
+  char user_path_other[64];
   /** Type. */
   eXrActionType type;
   /** State. Set appropriately based on type. */

source/blender/windowmanager/xr/intern/wm_xr_session.c

@@ -1025,6 +1025,10 @@ static wmXrActionData *wm_xr_session_event_create(const char *action_set_name,
   wmXrActionData *data = MEM_callocN(sizeof(wmXrActionData), __func__);
   strcpy(data->action_set, action_set_name);
   strcpy(data->action, action->name);
+  strcpy(data->user_path, action->subaction_paths[subaction_idx]);
+  if (bimanual) {
+    strcpy(data->user_path_other, action->subaction_paths[subaction_idx_other]);
+  }
   data->type = action->type;
 
   switch (action->type) {