layout: Use promise to wait for background to load

This allows us to separate the end of the loading operation
from the steps that follow it. We will soon use that to
express the startup animation as a series of (async) steps
instead of a chain of function calls.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3988>

diff --git a/js/ui/layout.js b/js/ui/layout.js
index 170a5d49688e289f5e19a2a1bdd058fbde363343..4fd23fe3273401d44e872580310d782d524d4f17 100644 (file)
--- a/js/ui/layout.js
+++ b/js/ui/layout.js
@@ -678,6 +678,7 @@ export const LayoutManager = GObject.registerClass({
         });
         this._systemBackground.add_constraint(constraint);
 
+        const {promise, resolve} = Promise.withResolvers();
         const signalId = this._systemBackground.connect('loaded', () => {
             this._systemBackground.disconnect(signalId);
 
@@ -688,13 +689,17 @@ export const LayoutManager = GObject.registerClass({
             // This helps to prevent us from running the animation
             // when the system is bogged down
             const id = GLib.idle_add(GLib.PRIORITY_LOW, () => {
-                this._systemBackground.show();
-                global.stage.show();
-                this._prepareStartupAnimation().catch(logError);
+                resolve();
                 return GLib.SOURCE_REMOVE;
             });
             GLib.Source.set_name_by_id(id, '[gnome-shell] Startup Animation');
         });
+
+        await promise;
+
+        this._systemBackground.show();
+        global.stage.show();
+        this._prepareStartupAnimation().catch(logError);
     }
 
     // Startup Animations