workspace: Sort windows in overview grid using cached center

When accessing properties on ClutterActor for size and position there is
a notable access time overhead. This overhead adds considerable user lag
when opening the overview if many windows are open.

This is primarily due to these properties being accessed while sorting
WindowClone instances by their window's center for placement in the
overview. By pre-computing this center value only once when
initializing WindowClone, the induced lag can be significantly reduced.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/763

diff --git a/js/ui/workspace.js b/js/ui/workspace.js
index ac53fa41cddb6afc408f603b060b42acd17ab41b..acad9eaf70570c380b80845995bd52802e64cf00 100644 (file)
--- a/js/ui/workspace.js
+++ b/js/ui/workspace.js
@@ -158,6 +158,8 @@ var WindowClone = GObject.registerClass({
         this.x = this._boundingBox.x;
         this.y = this._boundingBox.y;
 
+        this._computeWindowCenter();
+
         let clickAction = new Clutter.ClickAction();
         clickAction.connect('clicked', this._onClicked.bind(this));
         clickAction.connect('long-press', this._onLongPress.bind(this));
@@ -293,6 +295,18 @@ var WindowClone = GObject.registerClass({
         this.layout_manager.boundingBox = rect;
     }
 
+    get windowCenter() {
+        return this._windowCenter;
+    }
+
+    _computeWindowCenter() {
+        let box = this.realWindow.get_allocation_box();
+        this._windowCenter = new Clutter.Point({
+            x: box.get_x() + box.get_width() / 2,
+            y: box.get_y() + box.get_height() / 2,
+        });
+    }
+
     // Find the actor just below us, respecting reparenting done by DND code
     getActualStackAbove() {
         if (this._stackAbove == null)
@@ -1017,11 +1031,7 @@ var UnalignedLayoutStrategy = class extends LayoutStrategy {
     _sortRow(row) {
         // Sort windows horizontally to minimize travel distance.
         // This affects in what order the windows end up in a row.
-        row.windows.sort((a, b) => {
-            let aCenter = a.realWindow.x + a.realWindow.width / 2;
-            let bCenter = b.realWindow.x + b.realWindow.width / 2;
-            return aCenter - bCenter;
-        });
+        row.windows.sort((a, b) => a.windowCenter.x - b.windowCenter.x);
     }
 
     computeLayout(windows, layout) {
@@ -1040,11 +1050,7 @@ var UnalignedLayoutStrategy = class extends LayoutStrategy {
         // Sort windows vertically to minimize travel distance.
         // This affects what rows the windows get placed in.
         let sortedWindows = windows.slice();
-        sortedWindows.sort((a, b) => {
-            let aCenter = a.realWindow.y + a.realWindow.height / 2;
-            let bCenter = b.realWindow.y + b.realWindow.height / 2;
-            return aCenter - bCenter;
-        });
+        sortedWindows.sort((a, b) => a.windowCenter.y - b.windowCenter.y);
 
         let windowIdx = 0;
         for (let i = 0; i < numRows; i++) {