[gnome-shell] workspaceThumbnails: Center thumbnails in workspace navigator

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

commit de299f0a9069072d4c69d0fa2975e3c3a928068c
Author: Florian Müllner <fmuellner gnome org>
Date:   Mon Feb 1 16:28:49 2021 +0100

    workspaceThumbnails: Center thumbnails in workspace navigator
    
    We always request a natural width based on the maximum thumbnail scale,
    but may very well use a smaller scale when allocating. This currently
    results in thumbnails being off center, fix this by distributing any
    extra space evenly before allocating thumbnails.
    
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1620>

 js/ui/workspaceThumbnail.js | 7 +++++++
 1 file changed, 7 insertions(+)
---
diff --git a/js/ui/workspaceThumbnail.js b/js/ui/workspaceThumbnail.js
index 73f25593bd..46de36fa47 100644
--- a/js/ui/workspaceThumbnail.js
+++ b/js/ui/workspaceThumbnail.js
@@ -1302,6 +1302,13 @@ var ThumbnailsBox = GObject.registerClass({
         const thumbnailWidth = Math.round(thumbnailHeight * ratio);
         const roundedVScale = thumbnailHeight / portholeHeight;
 
+        // We always request size for MAX_THUMBNAIL_SCALE, distribute
+        // space evently if we use smaller thumbnails
+        const extraWidth =
+            (MAX_THUMBNAIL_SCALE * portholeWidth - thumbnailWidth) * nWorkspaces;
+        box.x1 += Math.round(extraWidth / 2);
+        box.x2 -= Math.round(extraWidth / 2);
+
         let indicatorValue = this._scrollAdjustment.value;
         let indicatorUpperWs = Math.ceil(indicatorValue);
         let indicatorLowerWs = Math.floor(indicatorValue);