workspacesView: Add minimap on secondary monitors

The workspace minimap is much less prominent than the old workspace
switcher, and serves primarily as an indicator.

That means that duplicating it on secondary monitors (if workspaces
on non-primaries are enabled) is harder to mistake for per-monitor
workspaces, so make some people happy by including the minimap on
every monitor.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1735>

data/theme/gnome-shell-sass/widgets/_overview.scss

@@ -1,6 +1,6 @@
 /* OVERVIEW */
 
-.controls-manager {
+.controls-manager, .secondary-monitor-workspaces {
   spacing: 24px;
 }
 

js/ui/workspacesView.js

@@ -9,6 +9,7 @@ const OverviewControls = imports.ui.overviewControls;
 const SwipeTracker = imports.ui.swipeTracker;
 const Util = imports.misc.util;
 const Workspace = imports.ui.workspace;
+const { ThumbnailsBox, MAX_THUMBNAIL_SCALE } = imports.ui.workspaceThumbnail;
 
 var WORKSPACE_SWITCH_TIME = 250;
 
@@ -604,6 +605,7 @@ class SecondaryMonitorDisplay extends St.Widget {
         this._overviewAdjustment = overviewAdjustment;
 
         super._init({
+            style_class: 'secondary-monitor-workspaces',
             constraints: new Layout.MonitorConstraint({
                 index: this._monitorIndex,
                 work_area: true,
@@ -612,13 +614,58 @@ class SecondaryMonitorDisplay extends St.Widget {
 
         this.connect('destroy', () => this._onDestroy());
 
+        this._thumbnails = new ThumbnailsBox(
+            this._scrollAdjustment, monitorIndex);
+        this.add_child(this._thumbnails);
+
+        this._thumbnails.connect('notify::should-show',
+            () => this._updateThumbnailVisibility());
+
+        this._stateChangedId = this._overviewAdjustment.connect('notify::value',
+            () => this._updateThumbnailParams());
+
         this._settings = new Gio.Settings({ schema_id: MUTTER_SCHEMA });
         this._settings.connect('changed::workspaces-only-on-primary',
-            () => this._updateWorkspacesView());
-        this._updateWorkspacesView();
+            () => this._workspacesOnPrimaryChanged());
+        this._workspacesOnPrimaryChanged();
     }
 
-    _getWorkspacesBoxForState(state, box, padding) {
+    _getThumbnailParamsForState(state) {
+        const { ControlsState } = OverviewControls;
+
+        let opacity, scale;
+        switch (state) {
+        case ControlsState.HIDDEN:
+        case ControlsState.WINDOW_PICKER:
+            opacity = 255;
+            scale = 1;
+            break;
+        case ControlsState.APP_GRID:
+            opacity = 0;
+            scale = 0.5;
+            break;
+        default:
+            opacity = 255;
+            scale = 1;
+            break;
+        }
+
+        return { opacity, scale };
+    }
+
+    _getThumbnailsHeight(box) {
+        if (!this._thumbnails.visible)
+            return 0;
+
+        const [width, height] = box.get_size();
+        const { expandFraction } = this._thumbnails;
+        const [thumbnailsHeight] = this._thumbnails.get_preferred_height(width);
+        return Math.min(
+            thumbnailsHeight * expandFraction,
+            height * MAX_THUMBNAIL_SCALE);
+    }
+
+    _getWorkspacesBoxForState(state, box, padding, thumbnailsHeight, spacing) {
         const { ControlsState } = OverviewControls;
         const workspaceBox = box.copy();
         const [width, height] = workspaceBox.get_size();
@@ -627,6 +674,11 @@ class SecondaryMonitorDisplay extends St.Widget {
         case ControlsState.HIDDEN:
             break;
         case ControlsState.WINDOW_PICKER:
+            workspaceBox.set_origin(0, padding + thumbnailsHeight + spacing);
+            workspaceBox.set_size(
+                width,
+                height - 2 * padding - thumbnailsHeight - spacing);
+            break;
         case ControlsState.APP_GRID:
             workspaceBox.set_origin(0, padding);
             workspaceBox.set_size(
@@ -643,16 +695,27 @@ class SecondaryMonitorDisplay extends St.Widget {
 
         const themeNode = this.get_theme_node();
         const contentBox = themeNode.get_content_box(box);
-        const [, height] = contentBox.get_size();
+        const [width, height] = contentBox.get_size();
+        const { expandFraction } = this._thumbnails;
+        const spacing = themeNode.get_length('spacing') * expandFraction;
         const padding =
             Math.round((1 - SECONDARY_WORKSPACE_SCALE) * height / 2);
 
+        const thumbnailsHeight = this._getThumbnailsHeight(contentBox);
+
+        if (this._thumbnails.visible) {
+            const childBox = new Clutter.ActorBox();
+            childBox.set_origin(0, padding);
+            childBox.set_size(width, thumbnailsHeight);
+            this._thumbnails.allocate(childBox);
+        }
+
         const {
             currentState, initialState, finalState, transitioning, progress,
         } = this._overviewAdjustment.getStateTransitionParams();
 
         let workspacesBox;
-        const workspaceParams = [contentBox, padding];
+        const workspaceParams = [contentBox, padding, thumbnailsHeight, spacing];
         if (!transitioning) {
             workspacesBox =
                 this._getWorkspacesBoxForState(currentState, ...workspaceParams);
@@ -670,6 +733,15 @@ class SecondaryMonitorDisplay extends St.Widget {
         if (this._settings)
             this._settings.run_dispose();
         this._settings = null;
+
+        if (this._stateChangedId)
+            this._overviewAdjustment.disconnect(this._stateChangedId);
+        this._stateChangedId = 0;
+    }
+
+    _workspacesOnPrimaryChanged() {
+        this._updateWorkspacesView();
+        this._updateThumbnailVisibility();
     }
 
     _updateWorkspacesView() {
@@ -691,6 +763,41 @@ class SecondaryMonitorDisplay extends St.Widget {
         this.add_child(this._workspacesView);
     }
 
+    _updateThumbnailVisibility() {
+        const visible =
+            this._thumbnails.should_show &&
+            !this._settings.get_boolean('workspaces-only-on-primary');
+
+        if (this._thumbnails.visible === visible)
+            return;
+
+        this._thumbnails.show();
+        this._thumbnails.ease_property('expand-fraction', visible ? 1 : 0, {
+            duration: OverviewControls.SIDE_CONTROLS_ANIMATION_TIME,
+            mode: Clutter.AnimationMode.EASE_OUT_QUAD,
+            onComplete: () => (this._thumbnails.visible = visible),
+        });
+    }
+
+    _updateThumbnailParams() {
+        const { initialState, finalState, progress } =
+            this._overviewAdjustment.getStateTransitionParams();
+
+        const initialParams = this._getThumbnailParamsForState(initialState);
+        const finalParams = this._getThumbnailParamsForState(finalState);
+
+        const opacity =
+            Util.lerp(initialParams.opacity, finalParams.opacity, progress);
+        const scale =
+            Util.lerp(initialParams.scale, finalParams.scale, progress);
+
+        this._thumbnails.set({
+            opacity,
+            scale_x: scale,
+            scale_y: scale,
+        });
+    }
+
     getActiveWorkspace() {
         return this._workspacesView.getActiveWorkspace();
     }