From 0a7507c617c08dbbccb4549665b87cf340f97e1c Mon Sep 17 00:00:00 2001
From: Sebastian Keller <skeller@gnome.org>
Date: Tue, 11 May 2021 16:43:37 +0200
Subject: [PATCH] altTab: Avoid allocation cycle when showing CyclerHighlight

CyclerHighlight was showing and resizing one of its child widgets when
its own allocation was changed, queuing another relayout, resulting in
allocation cycle warnings. Avoid this by updating the size of the
highlight when the frame rect of window has changes rather than the size
of the CyclerHighlight actor itself.

Related: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/4167
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1842>
---
 js/ui/altTab.js | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/js/ui/altTab.js b/js/ui/altTab.js
index bc8b17fac..6af9380ed 100644
--- a/js/ui/altTab.js
+++ b/js/ui/altTab.js
@@ -402,6 +402,7 @@ class CyclerHighlight extends St.Widget {
     _init() {
         super._init({ layout_manager: new Clutter.BinLayout() });
         this._window = null;
+        this._sizeChangedId = 0;
 
         this._clone = new Clutter.Clone();
         this.add_actor(this._clone);
@@ -415,7 +416,6 @@ class CyclerHighlight extends St.Widget {
 
         this.add_constraint(constraint);
 
-        this.connect('notify::allocation', this._onAllocationChanged.bind(this));
         this.connect('destroy', this._onDestroy.bind(this));
     }
 
@@ -423,6 +423,9 @@ class CyclerHighlight extends St.Widget {
         if (this._window == w)
             return;
 
+        if (this._sizeChangedId)
+            this._window.disconnect(this._sizeChangedId);
+
         this._window = w;
 
         if (this._clone.source)
@@ -434,21 +437,27 @@ class CyclerHighlight extends St.Widget {
             windowActor.hide();
 
         this._clone.source = windowActor;
-    }
 
-    _onAllocationChanged() {
-        if (!this._window) {
+        if (this._window) {
+            this._onSizeChanged();
+            this._sizeChangedId = this._window.connect('size-changed',
+                this._onSizeChanged.bind(this));
+        } else {
             this._highlight.set_size(0, 0);
             this._highlight.hide();
-        } else {
-            let [x, y] = this.allocation.get_origin();
-            let rect = this._window.get_frame_rect();
-            this._highlight.set_size(rect.width, rect.height);
-            this._highlight.set_position(rect.x - x, rect.y - y);
-            this._highlight.show();
         }
     }
 
+    _onSizeChanged() {
+        const bufferRect = this._window.get_buffer_rect();
+        const rect = this._window.get_frame_rect();
+        this._highlight.set_size(rect.width, rect.height);
+        this._highlight.set_position(
+            rect.x - bufferRect.x,
+            rect.y - bufferRect.y);
+        this._highlight.show();
+    }
+
     _onDestroy() {
         this.window = null;
     }