workspacesView: Scale inactive workspaces

As per the latest mockups, then horizontally snapping, the active
workspace should be highlighted. Because WorkspacesView clips to
allocation, we cannot simply scale up the active one. Instead,
scale down the inactive ones.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1613>

js/ui/workspace.js

@@ -1,7 +1,7 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
 /* exported Workspace */
 
-const { Clutter, GLib, GObject, Meta, St } = imports.gi;
+const { Clutter, GLib, GObject, Graphene, Meta, St } = imports.gi;
 
 const Background = imports.ui.background;
 const DND = imports.ui.dnd;
@@ -936,6 +936,7 @@ class Workspace extends St.Widget {
     _init(metaWorkspace, monitorIndex) {
         super._init({
             style_class: 'window-picker',
+            pivot_point: new Graphene.Point({ x: 0.5, y: 0.5 }),
             layout_manager: new WorkspaceLayout(metaWorkspace, monitorIndex),
             reactive: true,
         });

js/ui/workspacesView.js

@@ -17,6 +17,8 @@ const MUTTER_SCHEMA = 'org.gnome.mutter';
 const WORKSPACE_MIN_SPACING = 24;
 const WORKSPACE_MAX_SPACING = 80;
 
+const WORKSPACE_INACTIVE_SCALE = 0.94;
+
 var WorkspacesViewBase = GObject.registerClass({
     GTypeFlags: GObject.TypeFlags.ABSTRACT,
 }, class WorkspacesViewBase extends St.Widget {
@@ -83,6 +85,7 @@ class WorkspacesView extends WorkspacesViewBase {
         this._fitModeAdjustment = fitModeAdjustment;
         this._fitModeNotifyId = this._fitModeAdjustment.connect('notify::value', () => {
             this._updateVisibility();
+            this._updateWorkspacesState();
             this.queue_relayout();
         });
 
@@ -212,6 +215,20 @@ class WorkspacesView extends WorkspacesViewBase {
         return Math.clamp(spacing, WORKSPACE_MIN_SPACING, WORKSPACE_MAX_SPACING);
     }
 
+    _updateWorkspacesState() {
+        const adj = this._scrollAdjustment;
+
+        // Fade and scale inactive workspaces
+        this._workspaces.forEach((w, index) => {
+            const distanceToCurrentWorkspace = Math.abs(adj.value - index);
+
+            const progress = 1 - Math.clamp(distanceToCurrentWorkspace, 0, 1);
+
+            const scale = Util.lerp(WORKSPACE_INACTIVE_SCALE, 1, progress);
+            w.set_scale(scale, scale);
+        });
+    }
+
     vfunc_allocate(box) {
         this.set_allocation(box);
 
@@ -349,6 +366,8 @@ class WorkspacesView extends WorkspacesViewBase {
             this._workspaces[j].destroy();
             this._workspaces.splice(j, 1);
         }
+
+        this._updateWorkspacesState();
     }
 
     _activeWorkspaceChanged(_wm, _from, _to, _direction) {
@@ -411,6 +430,7 @@ class WorkspacesView extends WorkspacesViewBase {
             metaWorkspace.activate(global.get_current_time());
         }
 
+        this._updateWorkspacesState();
         this.queue_relayout();
     }
 });