[mutter/wip/carlosg/sync-pointer-in-mutter: 6/6] backends/x11: Emulate pointer motion while the pointer is off stage

[Marge Bot <marge-bot src gnome org>]

commit a5db9ee2d78ba746a3bc4bcfd11f7ebcd94fc5f5
Author: Carlos Garnacho <carlosg gnome org>
Date:   Tue Dec 29 11:30:22 2020 +0100

    backends/x11: Emulate pointer motion while the pointer is off stage
    
    Given X11 nature, the pointer "leaves" the stage anytime it wanders into
    a client window, or any other areas that are not deemed part of the
    stage input region.
    
    Yet we want to stay correct in those situations, e.g. have the clutter
    side reasonably in sync, picking and highlighting to work properly, etc.
    
    In order to achieve that, emulate motion events on XI_RawMotion. These
    are as much throttled as our pointer tracking for a11y, in order to avoid
    too many XIQueryPointer sync calls. This emulation only kicks in anytime
    that X11 notifies us that we are not "on" the stage.
    
    This replaces some sync_pointer() calls in GNOME Shell code that are
    there just to compensate for this trait of X11, e.g. in the message tray
    code.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1659>

 src/backends/x11/meta-seat-x11.c | 49 ++++++++++++++++++++++++++++++++++------
 1 file changed, 42 insertions(+), 7 deletions(-)
---
diff --git a/src/backends/x11/meta-seat-x11.c b/src/backends/x11/meta-seat-x11.c
index 009d596fe9..1e0d19120f 100644
--- a/src/backends/x11/meta-seat-x11.c
+++ b/src/backends/x11/meta-seat-x11.c
@@ -73,6 +73,7 @@ struct _MetaSeatX11
   int opcode;
   guint has_touchscreens : 1;
   guint touch_mode : 1;
+  guint has_pointer_focus : 1;
 };
 
 static GParamSpec *props[N_PROPS] = { 0 };
@@ -871,6 +872,29 @@ translate_property_event (MetaSeatX11 *seat_x11,
     }
 }
 
+static void
+emulate_motion (MetaSeatX11 *seat_x11,
+                double       x,
+                double       y)
+{
+  ClutterInputDevice *pointer;
+  ClutterEvent *event;
+  ClutterStage *stage;
+
+  pointer = clutter_seat_get_pointer (CLUTTER_SEAT (seat_x11));
+  stage = CLUTTER_STAGE (meta_backend_get_stage (meta_get_backend ()));
+
+  event = clutter_event_new (CLUTTER_MOTION);
+  clutter_event_set_flags (event, CLUTTER_EVENT_FLAG_SYNTHETIC);
+  clutter_event_set_coords (event, x, y);
+  clutter_event_set_device (event, pointer);
+  clutter_event_set_source_device (event, NULL);
+  clutter_event_set_stage (event, stage);
+
+  clutter_event_put (event);
+  clutter_event_free (event);
+}
+
 static void
 translate_raw_event (MetaSeatX11 *seat_x11,
                      XEvent      *xevent)
@@ -890,9 +914,6 @@ translate_raw_event (MetaSeatX11 *seat_x11,
   if (device == NULL)
     return;
 
-  if (!_clutter_is_input_pointer_a11y_enabled (device))
-    return;
-
   switch (cookie->evtype)
     {
     case XI_RawMotion:
@@ -906,7 +927,12 @@ translate_raw_event (MetaSeatX11 *seat_x11,
        * so we need to explicitly query the pointer here...
        */
       if (meta_input_device_x11_get_pointer_location (device, &x, &y))
-        _clutter_input_pointer_a11y_on_motion_event (device, x, y);
+        {
+          if (_clutter_is_input_pointer_a11y_enabled (device))
+            _clutter_input_pointer_a11y_on_motion_event (device, x, y);
+          if (!seat_x11->has_pointer_focus)
+            emulate_motion (seat_x11, x, y);
+        }
       break;
     case XI_RawButtonPress:
     case XI_RawButtonRelease:
@@ -917,9 +943,12 @@ translate_raw_event (MetaSeatX11 *seat_x11,
                meta_input_device_x11_get_device_id (device),
                clutter_input_device_get_device_name (device),
                xev->detail);
-      _clutter_input_pointer_a11y_on_button_event (device,
-                                                  xev->detail,
-                                                  (cookie->evtype == XI_RawButtonPress));
+      if (_clutter_is_input_pointer_a11y_enabled (device))
+        {
+          _clutter_input_pointer_a11y_on_button_event (device,
+                                                       xev->detail,
+                                                       (cookie->evtype == XI_RawButtonPress));
+        }
       break;
     }
 }
@@ -2291,6 +2320,9 @@ meta_seat_x11_translate_event (MetaSeatX11  *seat,
 
             event->crossing.time = xev->time;
             translate_coords (stage_x11, xev->event_x, xev->event_y, &event->crossing.x, &event->crossing.y);
+
+            if (xev->deviceid == seat->pointer_id)
+              seat->has_pointer_focus = TRUE;
           }
         else
           {
@@ -2302,6 +2334,9 @@ meta_seat_x11_translate_event (MetaSeatX11  *seat,
 
             event->crossing.time = xev->time;
             translate_coords (stage_x11, xev->event_x, xev->event_y, &event->crossing.x, &event->crossing.y);
+
+            if (xev->deviceid == seat->pointer_id)
+              seat->has_pointer_focus = FALSE;
           }
 
         meta_input_device_x11_reset_scroll_info (source_device);