[gnome-shell] appDisplay: Fix pages getting "stuck" under touch

[Jasper St. Pierre <jstpierre src gnome org>]

commit 82ec6c08b8c0b46311687930aa2135119949e40b
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Sun Apr 27 11:05:10 2014 -0400

    appDisplay: Fix pages getting "stuck" under touch
    
    We often call goToPage like:
    
      this.goToPage(this._currentPage - 1);
    
    (or + 1). During panning, these are based on the velocity values
    of the gesture action. If we're already on the first or last page
    and the panning ends, it's possible to get goToPage that's either
    -1 or greater than the last page.
    
    During normal usage, this isn't a problem, since the Y values will
    be correct, always. But when panning, the Y values stick to the
    finger, and thus if we return early, we won't snap to the exact page,
    making it seem like things get "stuck".
    
    Fix this the simple way by clamping to the correctly-ranged values
    of pageNumber
    
    https://bugzilla.gnome.org/show_bug.cgi?id=729064

 js/ui/appDisplay.js |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/js/ui/appDisplay.js b/js/ui/appDisplay.js
index 2596929..0f5baf8 100644
--- a/js/ui/appDisplay.js
+++ b/js/ui/appDisplay.js
@@ -81,6 +81,10 @@ function _getFolderName(folder) {
     return name;
 }
 
+function clamp(value, min, max) {
+    return Math.max(min, Math.min(max, value));
+}
+
 const BaseAppView = new Lang.Class({
     Name: 'BaseAppView',
     Abstract: true,
@@ -439,8 +443,8 @@ const AllView = new Lang.Class({
     },
 
     goToPage: function(pageNumber) {
-        if(pageNumber < 0 || pageNumber > this._grid.nPages() - 1)
-            return;
+        pageNumber = clamp(pageNumber, 0, this._grid.nPages() - 1);
+
         if (this._currentPage == pageNumber && this._displayingPopup && this._currentPopup)
             return;
         if (this._displayingPopup && this._currentPopup)