workspaceThumbnails: Animate showing/hiding

Right now the minimap only hides itself in case of a single static
workspace. That's not only an edge case, but also not expected to
change while the overview is visible, so changing the visibility
without a transition is fine.

However that is about to change, and we'll hide the minimap as well
when there are fewer than three workspaces. As that condition is
very much expected to change from within the overview, the transition
should be animated.

Implement that via a new :collapse-fraction property on ThumbnailsBox,
and use that to transition both the height of the box itself and the
scale of the individual thumbnails.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/3739

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1696>

js/ui/overviewControls.js

@@ -47,6 +47,7 @@ class ControlsManagerLayout extends Clutter.BoxLayout {
         const workspaceBox = box.copy();
         const [width, height] = workspaceBox.get_size();
         const { spacing } = this;
+        const { expandFraction } = this._workspacesThumbnails;
 
         switch (state) {
         case ControlsState.HIDDEN:
@@ -54,12 +55,12 @@ class ControlsManagerLayout extends Clutter.BoxLayout {
         case ControlsState.WINDOW_PICKER:
             workspaceBox.set_origin(0,
                 searchHeight + spacing +
-                (thumbnailsHeight > 0 ? thumbnailsHeight + spacing : 0));
+                thumbnailsHeight + spacing * expandFraction);
             workspaceBox.set_size(width,
                 height -
                 dashHeight - spacing -
                 searchHeight - spacing -
-                (thumbnailsHeight > 0 ? thumbnailsHeight + spacing : 0));
+                thumbnailsHeight - spacing * expandFraction);
             break;
         case ControlsState.APP_GRID:
             workspaceBox.set_origin(0, searchHeight + spacing);
@@ -133,10 +134,11 @@ class ControlsManagerLayout extends Clutter.BoxLayout {
         // Workspace Thumbnails
         let thumbnailsHeight = 0;
         if (this._workspacesThumbnails.visible) {
+            const { expandFraction } = this._workspacesThumbnails;
             [thumbnailsHeight] =
                 this._workspacesThumbnails.get_preferred_height(width);
             thumbnailsHeight = Math.min(
-                thumbnailsHeight,
+                thumbnailsHeight * expandFraction,
                 height * WorkspaceThumbnail.MAX_THUMBNAIL_SCALE);
             childBox.set_origin(0, searchHeight + spacing);
             childBox.set_size(width, thumbnailsHeight);
@@ -303,8 +305,15 @@ class ControlsManager extends St.Widget {
 
         this._thumbnailsBox =
             new WorkspaceThumbnail.ThumbnailsBox(this._workspaceAdjustment);
-        this._thumbnailsBox.connect('notify::should-show',
+        this._thumbnailsBox.connect('notify::should-show', () => {
-            () => this._updateThumbnailsBox());
+            this._thumbnailsBox.show();
+            this._thumbnailsBox.ease_property('expand-fraction',
+                this._thumbnailsBox.should_show ? 1 : 0, {
+                    duration: SIDE_CONTROLS_ANIMATION_TIME,
+                    mode: Clutter.AnimationMode.EASE_OUT_QUAD,
+                    onComplete: () => this._updateThumbnailsBox(),
+                });
+        });
 
         this._workspacesDisplay = new WorkspacesView.WorkspacesDisplay(
             this,

js/ui/workspaceThumbnail.js

@@ -603,6 +603,10 @@ var WorkspaceThumbnail = GObject.registerClass({
 
 var ThumbnailsBox = GObject.registerClass({
     Properties: {
+        'expand-fraction': GObject.ParamSpec.double(
+            'expand-fraction', 'expand-fraction', 'expand-fraction',
+            GObject.ParamFlags.READWRITE,
+            0, 1, 1),
         'scale': GObject.ParamSpec.double(
             'scale', 'scale', 'scale',
             GObject.ParamFlags.READWRITE,
@@ -643,6 +647,7 @@ var ThumbnailsBox = GObject.registerClass({
 
         this._targetScale = 0;
         this._scale = 0;
+        this._expandFraction = 1;
         this._pendingScaleUpdate = false;
         this._stateUpdateQueued = false;
         this._animatingIndicator = false;
@@ -1298,8 +1303,9 @@ var ThumbnailsBox = GObject.registerClass({
         }
 
         const ratio = portholeWidth / portholeHeight;
-        const thumbnailHeight = Math.round(portholeHeight * this._scale);
+        const thumbnailFullHeight = Math.round(portholeHeight * this._scale);
-        const thumbnailWidth = Math.round(thumbnailHeight * ratio);
+        const thumbnailWidth = Math.round(thumbnailFullHeight * ratio);
+        const thumbnailHeight = thumbnailFullHeight * this._expandFraction;
         const roundedVScale = thumbnailHeight / portholeHeight;
 
         // We always request size for MAX_THUMBNAIL_SCALE, distribute
@@ -1422,4 +1428,16 @@ var ThumbnailsBox = GObject.registerClass({
     get shouldShow() {
         return this._shouldShow;
     }
+
+    set expandFraction(expandFraction) {
+        if (this._expandFraction === expandFraction)
+            return;
+        this._expandFraction = expandFraction;
+        this.notify('expand-fraction');
+        this.queue_relayout();
+    }
+
+    get expandFraction() {
+        return this._expandFraction;
+    }
 });