magnifier: Properly hide the second (real) cursor

The magnifier uses a PointerWatcher (which is based on a simple timeout
source) to update the zoom region based on the current mouse cursor
position 60 times a second. When updating the zoom region, it would also
hide mutters cursor using meta_cursor_tracker_set_pointer_visible().

Since a few months, mutter has decoupled the handling of input events
from the monitor refresh rate though, which means it's no longer
guaranteed that the cursor changes only 60 times a second (on higher
refresh rate monitors it actually never was). This means mutter might
show the cursor more often than 60 times a second, while we hide it only
60 times a second, leading to a flickering second cursor.

To fix this, implement the cursor-hiding by listening to
MetaCursorTrackers visibility-changed signal, and immediately hiding the
cursor again when it's shown.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2234>

diff --git a/js/ui/magnifier.js b/js/ui/magnifier.js
index c0c750e8e095fd3cd6aa1132691fbccf32b00777..0585e8812e5c2b802c895ff1ea33a468ec4c8173 100644 (file)
--- a/js/ui/magnifier.js
+++ b/js/ui/magnifier.js
@@ -126,7 +126,13 @@ var Magnifier = class Magnifier {
 
         if (seat.is_unfocus_inhibited())
             seat.uninhibit_unfocus();
-        this._cursorTracker.set_pointer_visible(true);
+
+        if (this._cursorVisibilityChangedId) {
+            this._cursorTracker.disconnect(this._cursorVisibilityChangedId);
+            delete this._cursorVisibilityChangedId;
+
+            this._cursorTracker.set_pointer_visible(true);
+        }
     }
 
     /**
@@ -138,7 +144,14 @@ var Magnifier = class Magnifier {
 
         if (!seat.is_unfocus_inhibited())
             seat.inhibit_unfocus();
-        this._cursorTracker.set_pointer_visible(false);
+
+        if (!this._cursorVisibilityChangedId) {
+            this._cursorTracker.set_pointer_visible(false);
+            this._cursorVisibilityChangedId = this._cursorTracker.connect('visibility-changed', () => {
+                if (this._cursorTracker.get_pointer_visible())
+                    this._cursorTracker.set_pointer_visible(false);
+            });
+        }
     }
 
     /**