Don't synthesize mousemove events if the mouse cursor is not on the widget

ui/views/widget/widget.cc

 // Copyright (c) 2012 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/views/widget/widget.h"
 
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 151 matching lines @@
       ownership_(InitParams::NATIVE_WIDGET_OWNS_WIDGET),
       is_secondary_widget_(true),
       frame_type_(FRAME_TYPE_DEFAULT),
       disable_inactive_rendering_(false),
       widget_closed_(false),
       saved_show_state_(ui::SHOW_STATE_DEFAULT),
       focus_on_creation_(true),
       is_top_level_(false),
       native_widget_initialized_(false),
       native_widget_destroyed_(false),
+      is_mouse_on_widget_(false),
       is_mouse_button_pressed_(false),
       ignore_capture_loss_(false),
       last_mouse_event_was_move_(false),
       auto_release_capture_(true),
       root_layers_dirty_(false),
       movement_disabled_(false),
       observer_manager_(this) {
 }
 
 Widget::~Widget() {
@@ skipping 799 matching lines @@
 
 const TooltipManager* Widget::GetTooltipManager() const {
   return native_widget_->GetTooltipManager();
 }
 
 gfx::Rect Widget::GetWorkAreaBoundsInScreen() const {
   return native_widget_->GetWorkAreaBoundsInScreen();
 }
 
 void Widget::SynthesizeMouseMoveEvent() {
+  if (!is_mouse_on_widget_)
+    return;
+
   last_mouse_event_was_move_ = false;
   ui::MouseEvent mouse_event(ui::ET_MOUSE_MOVED, last_mouse_event_position_,
                              last_mouse_event_position_, ui::EventTimeForNow(),
                              ui::EF_IS_SYNTHESIZED, 0);
   root_view_->OnMouseMoved(mouse_event);
 }
 
 void Widget::OnRootViewLayout() {
   native_widget_->OnRootViewLayout();
 }
@@ skipping 222 matching lines @@
           root_view->OnMouseDragged(*event);
       } else if (!last_mouse_event_was_move_ ||
                  last_mouse_event_position_ != event->location()) {
         last_mouse_event_position_ = event->location();
         last_mouse_event_was_move_ = true;
         if (root_view)
           root_view->OnMouseMoved(*event);
       }
       return;
 
+    case ui::ET_MOUSE_ENTERED:
+      is_mouse_on_widget_ = true;
+      return;
+
     case ui::ET_MOUSE_EXITED:
+      is_mouse_on_widget_ = false;

[sky, 2015/08/20 18:03:12]

I'm worried we won't always get here. Say you click hold and drag, or we trigger
a nested message loop or other weird cases.
Here's a though, why do we cache the mouse location for
SynthesizeMouseMoveEvent. Why don't we query for the current mouse location in
SynthesizeMouseMoveEvent, that way you can detect if mouse is over widget or
not.

[oshima, 2015/08/21 01:00:15]

For drag case, the mouse location is outside of the widget, so this still should
work correctly. I think the nested message loop case won't affect this, although
I may be missing something.
This should work too, I think.

       last_mouse_event_was_move_ = false;
       if (root_view)
         root_view->OnMouseExited(*event);
       return;
 
     case ui::ET_MOUSEWHEEL:
       if (root_view && root_view->OnMouseWheel(
           static_cast<const ui::MouseWheelEvent&>(*event)))
         event->SetHandled();
       return;
@@ skipping 239 matching lines @@
 
 ////////////////////////////////////////////////////////////////////////////////
 // internal::NativeWidgetPrivate, NativeWidget implementation:
 
 internal::NativeWidgetPrivate* NativeWidgetPrivate::AsNativeWidgetPrivate() {
   return this;
 }
 
 }  // namespace internal
 }  // namespace views