[gnome-shell] AppDisplay: allow changing categories by scrolling over them

[Giovanni Campagna <gcampagna src gnome org>]

commit 88bcd0a9cea0789c279199e26ad55782e1e0e534
Author: Giovanni Campagna <gcampagna src gnome org>
Date:   Sun Feb 27 21:46:17 2011 +0100

    AppDisplay: allow changing categories by scrolling over them
    
    Respond to scrolling over the app categories by changing them, so
    it is not required to point and click, or to use the All view.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=643426

 js/ui/appDisplay.js |   22 +++++++++++++++++++++-
 1 files changed, 21 insertions(+), 1 deletions(-)
---
diff --git a/js/ui/appDisplay.js b/js/ui/appDisplay.js
index ebc19d1..6fe12f2 100644
--- a/js/ui/appDisplay.js
+++ b/js/ui/appDisplay.js
@@ -109,7 +109,14 @@ ViewByCategories.prototype = {
 
         this._view = new AlphabeticalView();
 
-        this._filters = new St.BoxLayout({ vertical: true });
+        // categories can be -1 (the All view) or 0...n-1, where n
+        // is the number of sections
+        // -2 is a flag to indicate that nothing is selected
+        // (used only before the actor is mapped the first time)
+        this._currentCategory = -2;
+        this._filters = new St.BoxLayout({ vertical: true, reactive: true });
+        this._filters.connect('scroll-event', Lang.bind(this, this._scrollFilter));
+
         this.actor.add(this._view.actor, { expand: true, x_fill: true, y_fill: true });
         this.actor.add(this._filters, { expand: false, y_fill: false, y_align: St.Align.START });
 
@@ -123,7 +130,20 @@ ViewByCategories.prototype = {
         this._sections = [];
     },
 
+    _scrollFilter: function(actor, event) {
+        let direction = event.get_scroll_direction();
+        if (direction == Clutter.ScrollDirection.UP)
+            this._selectCategory(Math.max(this._currentCategory - 1, -1))
+        else if (direction == Clutter.ScrollDirection.DOWN)
+            this._selectCategory(Math.min(this._currentCategory + 1, this._sections.length - 1));
+    },
+
     _selectCategory: function(num) {
+        if (this._currentCategory == num) // nothing to do
+            return;
+
+        this._currentCategory = num;
+
         if (num != -1)
             this._allFilter.remove_style_pseudo_class('selected');
         else