Add workspaceSwitchAction Clutter.GestureAction

This gesture implements 4-finger drag, that will be used for workspace
switching.

js/js-resources.gresource.xml

@@ -91,6 +91,7 @@
     <file>ui/windowMenu.js</file>
     <file>ui/windowManager.js</file>
     <file>ui/workspace.js</file>
+    <file>ui/workspaceSwitchAction.js</file>
     <file>ui/workspaceSwitcherPopup.js</file>
     <file>ui/workspaceThumbnail.js</file>
     <file>ui/workspacesView.js</file>

js/ui/workspaceSwitchAction.js

@@ -0,0 +1,52 @@
+// -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
+
+const Signals = imports.signals;
+const Lang = imports.lang;
+const Meta = imports.gi.Meta;
+const Clutter = imports.gi.Clutter;
+
+let MOTION_THRESHOLD = 50;
+
+const WorkspaceSwitchAction = new Lang.Class({
+    Name: 'WorkspaceSwitchAction',
+    Extends: Clutter.GestureAction,
+
+    _init : function() {
+        this.parent();
+        this.set_n_touch_points (4);
+        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() == this.get_n_touch_points();
+    },
+
+    vfunc_gesture_end : function(action, actor) {
+        // Just check one touchpoint here
+        let [startX, startY] = this.get_press_coords(0);
+        let [x, y] = this.get_motion_coords(0);
+        let offsetX = x - startX;
+        let offsetY = y - startY;
+        let direction;
+
+        if (Math.abs(offsetX) < MOTION_THRESHOLD &&
+            Math.abs(offsetY) < MOTION_THRESHOLD)
+            return;
+
+        if (Math.abs(offsetY) > Math.abs(offsetX)) {
+            if (offsetY > 0)
+                direction = Meta.MotionDirection.UP;
+            else
+                direction = Meta.MotionDirection.DOWN;
+        } else {
+            if (offsetX > 0)
+                direction = Meta.MotionDirection.LEFT;
+            else
+                direction = Meta.MotionDirection.RIGHT;
+        }
+
+        this.emit('activated', direction);
+    }
+});
+Signals.addSignalMethods(WorkspaceSwitchAction.prototype);