From 43b4f2c7d5f975ca6589970f284f5eb7d4ed45db Mon Sep 17 00:00:00 2001
From: Georges Basile Stavracas Neto <georges.stavracas@gmail.com>
Date: Thu, 12 Sep 2019 15:45:04 -0300
Subject: [PATCH] lookingGlass: Only update window list when visible

Updating the window list in the Looking Glass is a costly
operation: it destroys a whole lot of actors, and recreates
them. This triggers CSS changes, repaints, and allocations.

It is specially bad when paired with Wayland's big number
of window creations and deletions when showing Builder's
and Epiphany's popup window.

Only update the window list in the Looking Glass when it is
visible.

Related: https://gitlab.gnome.org/GNOME/mutter/issues/556

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/719
---
 js/ui/lookingGlass.js | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/js/ui/lookingGlass.js b/js/ui/lookingGlass.js
index 9f692f4aa..0317973e8 100644
--- a/js/ui/lookingGlass.js
+++ b/js/ui/lookingGlass.js
@@ -304,6 +304,9 @@ var WindowList = class WindowList {
     }
 
     _updateWindowList() {
+        if (!this._lookingGlass.isOpen)
+            return;
+
         this.actor.destroy_all_children();
         let windows = global.get_window_actors();
         let tracker = Shell.WindowTracker.get_default();
@@ -335,6 +338,10 @@ var WindowList = class WindowList {
             }
         }
     }
+
+    update() {
+        this._updateWindowList();
+    }
 };
 Signals.addSignalMethods(WindowList.prototype);
 
@@ -1099,6 +1106,8 @@ var LookingGlass = class LookingGlass {
             duration,
             mode: Clutter.AnimationMode.EASE_OUT_QUAD
         });
+
+        this._windowList.update();
     }
 
     close() {
@@ -1124,5 +1133,9 @@ var LookingGlass = class LookingGlass {
             onComplete: () => this.actor.hide()
         });
     }
+
+    get isOpen() {
+        return this._open;
+    }
 };
 Signals.addSignalMethods(LookingGlass.prototype);