Add AppSwitchAction Clutter.GestureAction

This action implements 3-finger hold + 4th finger tap to switch
the focused application.

js/js-resources.gresource.xml

@@ -32,6 +32,7 @@
     <file>ui/animation.js</file>
     <file>ui/appDisplay.js</file>
     <file>ui/appFavorites.js</file>
+    <file>ui/appSwitchAction.js</file>
     <file>ui/backgroundMenu.js</file>
     <file>ui/background.js</file>
     <file>ui/boxpointer.js</file>

js/ui/appSwitchAction.js

@@ -0,0 +1,64 @@
+// -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
+
+const Lang = imports.lang;
+const Signals = imports.signals;
+const Clutter = imports.gi.Clutter;
+
+//in milliseconds
+let LONG_PRESS_TIMEOUT = 250;
+
+let MOTION_THRESHOLD = 30;
+
+const AppSwitchAction = new Lang.Class({
+    Name: 'AppSwitchAction',
+    Extends: Clutter.GestureAction,
+
+    _init : function() {
+	this.parent();
+	this.set_n_touch_points (3);
+	global.display.connect('grab-op-begin', Lang.bind(this, this.cancel));
+	global.display.connect('grab-op-end', Lang.bind(this, this.cancel));
+    },
+
+    vfunc_gesture_prepare : function(action, actor) {
+	return this.get_n_current_points() <= 4;
+    },
+
+    vfunc_gesture_begin : function(action, actor) {
+	let nPoints = this.get_n_current_points();
+	let event = this.get_last_event (nPoints - 1);
+
+	if (nPoints == 3)
+	    this._longPressStartTime = event.get_time();
+	else if (nPoints == 4) {
+	    // Check whether the 4th finger press happens after a 3-finger long press,
+	    // this only needs to be checked on the first 4th finger press
+	    if (this._longPressStartTime != null &&
+		event.get_time() < this._longPressStartTime + LONG_PRESS_TIMEOUT)
+		this.cancel();
+	    else {
+		this._longPressStartTime = null;
+		this.emit('activated');
+	    }
+	}
+
+	return this.get_n_current_points() <= 4;
+    },
+
+    vfunc_gesture_progress : function(action, actor) {
+	if (this.get_n_current_points() == 3) {
+	    for (let i = 0; i < this.get_n_current_points(); i++) {
+		[startX, startY] = this.get_press_coords(i);
+		[x, y] = this.get_motion_coords(i);
+
+		if (Math.abs(x - startX) > MOTION_THRESHOLD ||
+		    Math.abs(y - startY) > MOTION_THRESHOLD)
+		    return false;
+	    }
+
+	}
+
+	return true;
+    }
+});
+Signals.addSignalMethods(AppSwitchAction.prototype);