[polari/gnome-3-36] mainWindow: Cache view-height to avoid notifying unconditionally on it

[Florian Müllner <fmuellner src gnome org>]

commit 955c9f844cfb4dabd8fb8b7eba36f20e4fbe738d
Author: Philip Withnall <withnall endlessm com>
Date:   Wed May 6 17:02:00 2020 +0100

    mainWindow: Cache view-height to avoid notifying unconditionally on it
    
    If the code notifies of changes to view-height unconditionally (i.e.
    even if the actual value of view-height hasn’t changed), it can lead to
    a lot of unnecessary resize cycles.
    
    Avoid that by storing the old value and only emitting a notification if
    it’s changed.
    
    Signed-off-by: Philip Withnall <withnall endlessm com>
    
    https://gitlab.gnome.org/GNOME/polari/-/merge_requests/157

 src/mainWindow.js | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)
---
diff --git a/src/mainWindow.js b/src/mainWindow.js
index dccf327f..bae235e2 100644
--- a/src/mainWindow.js
+++ b/src/mainWindow.js
@@ -140,8 +140,14 @@ var MainWindow = GObject.registerClass({
         if (GLib.get_application_name().toLowerCase().includes('snapshot'))
             this.get_style_context().add_class('snapshot');
 
+        this._viewHeight = this._calculateViewHeight();
         this._roomStack.connect('size-allocate', () => {
-            this.notify('view-height');
+            let oldViewHeight = this._viewHeight;
+            let newViewHeight = this._calculateViewHeight();
+            if (oldViewHeight !== newViewHeight) {
+                this._viewHeight = newViewHeight;
+                this.notify('view-height');
+            }
         });
 
         // command output notifications should not pop up over
@@ -219,9 +225,13 @@ var MainWindow = GObject.registerClass({
         return this._subtitle.length > 0;
     }
 
+    _calculateViewHeight() {
+        return this._roomStack.get_allocated_height() - this._roomStack.entry_area_height;
+    }
+
     // eslint-disable-next-line camelcase
     get view_height() {
-        return this._roomStack.get_allocated_height() - this._roomStack.entry_area_height;
+        return this._viewHeight;
     }
 
     _onAccountsReachableChanged() {