[gnome-shell/wip/pressure: 635/637] layout: Don't show the tray if the user is just skirting the barrier

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

commit 36fe76be342202d8a234613da690d5e30bc99531
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Tue Jul 31 10:58:58 2012 -0300

    layout: Don't show the tray if the user is just skirting the barrier
    
    If the user is just pushing their mouse along the barrier's edge, rather
    than pushing down onto the barrier, we shouldn't show the tray. Do this
    by keeping track of the distance traveled perpendicular to the barrier,
    and releasing the accumulated pressure if we pass a threshold.

 js/ui/layout.js |   35 ++++++++++++++++++++++++++---------
 1 files changed, 26 insertions(+), 9 deletions(-)
---
diff --git a/js/ui/layout.js b/js/ui/layout.js
index 35b9e1a..83f47ba 100644
--- a/js/ui/layout.js
+++ b/js/ui/layout.js
@@ -20,6 +20,10 @@ const KEYBOARD_ANIMATION_TIME = 0.5;
 const PLYMOUTH_TRANSITION_TIME = 1;
 
 const MESSAGE_TRAY_PRESSURE_THRESHOLD = 200;
+// The maximium amount that the user is allowed to travel
+// perpendicular to the barrier before we release the accumulated
+// pressure.
+const MESSAGE_TRAY_MAX_SKIRT = 100;
 
 const MonitorConstraint = new Lang.Class({
     Name: 'MonitorConstraint',
@@ -299,7 +303,9 @@ const LayoutManager = new Lang.Class({
                                                    y1: monitor.y + monitor.height, y2: monitor.y + monitor.height,
                                                    directions: Meta.BarrierDirection.NEGATIVE_Y });
 
-            this._trayPressure = new PressureBarrier(this._trayBarrier, MESSAGE_TRAY_PRESSURE_THRESHOLD);
+            this._trayPressure = new PressureBarrier(this._trayBarrier,
+                                                     MESSAGE_TRAY_PRESSURE_THRESHOLD,
+                                                     MESSAGE_TRAY_MAX_SKIRT);
             this._trayPressure.connect('trigger', function() {
                 Main.messageTray.openTray();
             });
@@ -1160,10 +1166,11 @@ Signals.addSignalMethods(Chrome.prototype);
 const PressureBarrier = new Lang.Class({
     Name: 'TrayPressure',
 
-    _init: function(barrier, threshold) {
+    _init: function(barrier, pressureThreshold, perpThreshold) {
         this._barrier = barrier;
-        this._threshold = threshold;
-        this._getVelocity = this._makeGetVelocity(barrier);
+        this._pressureThreshold = pressureThreshold;
+        this._perpThreshold = perpThreshold;
+        this._getVelocityAndPerp = this._makeGetVelocityAndPerp(barrier);
 
         this._reset(0);
 
@@ -1178,16 +1185,17 @@ const PressureBarrier = new Lang.Class({
     _reset: function(eventId) {
         this._currentEventId = eventId;
         this._currentPressure = 0;
+        this._perpAccumulator = 0;
     },
 
-    _makeGetVelocity: function(barrier) {
+    _makeGetVelocityAndPerp: function(barrier) {
         if (barrier.y1 === barrier.y2) {
             return function(event) {
-                return Math.abs(event.dy);
+                return [Math.abs(event.dy), event.dx];
             };
         } else {
             return function(event) {
-                return Math.abs(event.dx);
+                return [Math.abs(event.dx), event.dy];
             };
         }
     },
@@ -1200,10 +1208,19 @@ const PressureBarrier = new Lang.Class({
             this._reset(event.event_id);
         }
 
-        let velocity = this._getVelocity(event);
+        let [velocity, perp] = this._getVelocityAndPerp(event);
+        this._perpAccumulator += perp;
+
+        // If the user travels too far in the direction perpendicular
+        // to the barrier, start over from scratch -- the user is simply
+        // trying to skirt along the barrier.
+        if (Math.abs(this._perpAccumulator) >= this._perpThreshold) {
+            this._reset(0);
+            return;
+        }
 
         this._currentPressure += velocity;
-        if (this._currentPressure >= this._threshold) {
+        if (this._currentPressure >= this._pressureThreshold) {
             this.emit('trigger');
             this._reset(0);
         }