aura: Re-enable XInput2 events.

It turns out that the position information in an event for a slave device
reported by X is always slightly behind than the actual position. However, it
turns out that the valuators do contain the correct information. So get the
event location from the valuator.

BUG=103981
TEST=manually

Review URL: http://codereview.chromium.org/8568044

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@111016 0039d316-1c4b-4281-b951-d872f2087c98

ui/aura/desktop_host_linux.cc

@@ -281,11 +281,8 @@ DesktopHostLinux::DesktopHostLinux(const gfx::Rect& bounds)
   XSelectInput(xdisplay_, xwindow_, event_mask);
   XFlush(xdisplay_);
 
-  // TODO(sadrul): reenable once 103981 is fixed.
-#if defined(TOUCH_UI)
   if (base::MessagePumpForUI::HasXInput2())
     ui::TouchFactory::GetInstance()->SetupXI2ForXWindow(xwindow_);
-#endif
 }
 
 DesktopHostLinux::~DesktopHostLinux() {

ui/base/x/events_x.cc

@@ -248,8 +248,23 @@ gfx::Point EventLocationFromNative(const base::NativeEvent& native_event) {
     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.
+        // Prepare to be revolted.
+        double x = xievent->valuators.values[0] - (xievent->root_x -
+                                                   xievent->event_x);
+        double y = xievent->valuators.values[1] - (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();