aura: Re-enable XInput2 events.

ui/base/x/events_x.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/base/events.h"
 
 #include <X11/Xlib.h>
 #include <X11/extensions/XInput2.h>
 
 #include "base/logging.h"
@@ skipping 230 matching lines @@
 gfx::Point EventLocationFromNative(const base::NativeEvent& native_event) {
   switch (native_event->type) {
     case ButtonPress:
     case ButtonRelease:
       return gfx::Point(native_event->xbutton.x, native_event->xbutton.y);
     case MotionNotify:
       return gfx::Point(native_event->xmotion.x, native_event->xmotion.y);
     case GenericEvent: {
       XIDeviceEvent* xievent =
           static_cast<XIDeviceEvent*>(native_event->xcookie.data);
-      return gfx::Point(static_cast<int>(xievent->event_x),
-                        static_cast<int>(xievent->event_y));
+
+      if (xievent->sourceid == xievent->deviceid) {
+        // This event is coming from a slave device. Read the position from the
+        // valuators, because the events reported for a slave device seems to be
+        // behind the master device by one event. See more on crbug.com/103981.
+        // The position in the valuators is in the global screen coordinates.
+        // But it is necessary to convert it into the window's coordinates. If
+        // the valuator is not set, that means the value hasn't changed, and so
+        // we can use the value from event_x/event_y (which are in the window's
+        // coordinates).
+        double* valuators = xievent->valuators.values;
+
+        double x = xievent->event_x;
+        if (XIMaskIsSet(xievent->valuators.mask, 0))
+          x = *valuators++ - (xievent->root_x - xievent->event_x);
+
+        double y = xievent->event_y;
+        if (XIMaskIsSet(xievent->valuators.mask, 1))
+          y = *valuators++ - (xievent->root_y - xievent->event_y);
+
+        return gfx::Point(static_cast<int>(x), static_cast<int>(y));
+      } else {
+        return gfx::Point(static_cast<int>(xievent->event_x),
+                          static_cast<int>(xievent->event_y));
+      }
     }
   }
   return gfx::Point();
 }
 
 KeyboardCode KeyboardCodeFromNative(const base::NativeEvent& native_event) {
   return KeyboardCodeFromXKeyEvent(native_event);
 }
 
 bool IsMouseEvent(const base::NativeEvent& native_event) {
@@ skipping 96 matching lines @@
   static XEvent* noop = new XEvent();
   noop->xclient.type = ClientMessage;
   noop->xclient.display = NULL;
   noop->xclient.window = None;
   noop->xclient.message_type = 0;
   noop->xclient.format = 0;
   return noop;
 }
 
 }  // namespace ui