[gnome-shell] workspacesView: Avoid setting invalid geometries on views

[Florian Müllner <fmuellner src gnome org>]

commit baeb4079ee2f005e226fd85e4f9e88e234ffc93c
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Wed May 20 12:05:04 2020 +0200

    workspacesView: Avoid setting invalid geometries on views
    
    The fullGeometry and the actualGeometry of the WorkspacesDisplay are set
    from the allocation of the overviews ControlsManager and the
    WorkspacesDisplay, that means they're only valid after those actors got
    their allocations during Clutters allocation cycle.
    
    Since WorkspacesDisplay._updateWorkspacesViews() is already called while
    showing/mapping the WorkspacesDisplay, that allocation cycle didn't
    happen yet and we end up either setting the geometries of the views to
    null (in case of the fullGeometry) or to something wrong (a 0-sized
    allocation in case of the actualGeometry).
    
    So avoid setting invalid geometries on the views by initializing both
    the fullGeometry and the actualGeometry to null, and then only updating
    the geometries of the views after they're set to a correct value.
    
    Note that this means we won't correctly animate the overview the first
    time we open it since the animation depends on the geometries being set,
    but is being started from show(), which means no allocations have
    happened yet. In practice this introduces no regression though since
    before this change we simply used incorrect geometries (see the 0-sized
    allocation mentioned above) on the initial opening and the animation
    didn't work either.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1119

 js/ui/workspacesView.js | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)
---
diff --git a/js/ui/workspacesView.js b/js/ui/workspacesView.js
index 335344eb0a..e33528db0f 100644
--- a/js/ui/workspacesView.js
+++ b/js/ui/workspacesView.js
@@ -453,6 +453,7 @@ class WorkspacesDisplay extends St.Widget {
         this._keyPressEventId = 0;
         this._scrollTimeoutId = 0;
 
+        this._actualGeometry = null;
         this._fullGeometry = null;
         this._inWindowDrag = false;
 
@@ -696,8 +697,10 @@ class WorkspacesDisplay extends St.Widget {
 
         this._workspacesViews.forEach(v => v.show());
 
-        this._updateWorkspacesFullGeometry();
-        this._updateWorkspacesActualGeometry();
+        if (this._fullGeometry)
+            this._syncWorkspacesFullGeometry();
+        if (this._actualGeometry)
+            this._syncWorkspacesActualGeometry();
     }
 
     _getMonitorIndexForEvent(event) {
@@ -749,10 +752,10 @@ class WorkspacesDisplay extends St.Widget {
     // the sliding controls were never slid in at all.
     setWorkspacesFullGeometry(geom) {
         this._fullGeometry = geom;
-        this._updateWorkspacesFullGeometry();
+        this._syncWorkspacesFullGeometry();
     }
 
-    _updateWorkspacesFullGeometry() {
+    _syncWorkspacesFullGeometry() {
         if (!this._workspacesViews.length)
             return;
 
@@ -764,18 +767,21 @@ class WorkspacesDisplay extends St.Widget {
     }
 
     _updateWorkspacesActualGeometry() {
+        const [x, y] = this.get_transformed_position();
+        const width = this.allocation.get_width();
+        const height = this.allocation.get_height();
+
+        this._actualGeometry = { x, y, width, height };
+        this._syncWorkspacesActualGeometry();
+    }
+
+    _syncWorkspacesActualGeometry() {
         if (!this._workspacesViews.length)
             return;
 
-        let [x, y] = this.get_transformed_position();
-        let allocation = this.allocation;
-        let width = allocation.x2 - allocation.x1;
-        let height = allocation.y2 - allocation.y1;
-        let primaryGeometry = { x, y, width, height };
-
         let monitors = Main.layoutManager.monitors;
         for (let i = 0; i < monitors.length; i++) {
-            let geometry = i == this._primaryIndex ? primaryGeometry : monitors[i];
+            let geometry = i === this._primaryIndex ? this._actualGeometry : monitors[i];
             this._workspacesViews[i].setActualGeometry(geometry);
         }
     }