adding mouseMetrics to keep track of mousemovements

docs/docs/reference-events.md

@@ -203,6 +203,8 @@ number clientY
 boolean ctrlKey
 boolean getModifierState(key)
 boolean metaKey
+number movementX
+number movementY
 number pageX
 number pageY
 DOMEventTarget relatedTarget

src/renderers/dom/shared/syntheticEvents/SyntheticMouseEvent.js

@@ -13,6 +13,7 @@
 
 var SyntheticUIEvent = require('SyntheticUIEvent');
 var ViewportMetrics = require('ViewportMetrics');
+var MouseMetrics = require('MouseMetrics');
 
 var getEventModifierState = require('getEventModifierState');
 
@@ -29,6 +30,25 @@ var MouseEventInterface = {
   shiftKey: null,
   altKey: null,
   metaKey: null,
+  movementX: function(event) {
+    if ('movementX' in event) {
+      return event.movementX;
+    }
+
+    var previousScreenX = MouseMetrics.previousScreenX;
+    MouseMetrics.setPreviousScreenX(event.screenX);
+    return (previousScreenX) ? event.screenX - previousScreenX : 0;
+
+  },
+  movementY: function(event) {
+    if ('movementY' in event) {
+      return event.movementY;
+    }
+
+    var previousScreenY = MouseMetrics.previousScreenY;
+    MouseMetrics.setPreviousScreenY(event.screenY);
+    return previousScreenY ? event.screenY - previousScreenY : 0;
+  },
   getModifierState: getEventModifierState,
   button: function(event) {
     // Webkit, Firefox, IE9+

src/renderers/dom/shared/utils/MouseMetrics.js

@@ -0,0 +1,30 @@
+/**
+ * Copyright 2013-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @providesModule MouseMetrics
+ */
+
+'use strict';
+
+var MouseMetrics = {
+
+  previousScreenX: null,
+
+  previousScreenY: null,
+
+  setPreviousScreenX: function(value) {
+    MouseMetrics.previousScreenX = value;
+  },
+
+  setPreviousScreenY: function(value) {
+    MouseMetrics.previousScreenY = value;
+  },
+
+};
+
+module.exports = MouseMetrics;