X11: Avoid round-tripping to get the cursor position

ui/events/platform/x11/x11_event_source.h

 // Copyright 2014 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.
 
 #ifndef UI_EVENTS_PLATFORM_X11_X11_EVENT_SOURCE_H_
 #define UI_EVENTS_PLATFORM_X11_X11_EVENT_SOURCE_H_
 
 #include <stdint.h>
 
 #include <memory>
+#include <stack>
 
 #include "base/macros.h"
+#include "base/optional.h"
 #include "ui/events/events_export.h"
 #include "ui/gfx/x/x11_types.h"
 
 using Time = unsigned long;
 using XEvent = union _XEvent;
 using XID = unsigned long;
 using XWindow = unsigned long;
 
+namespace gfx {
+class Point;
+}
+
 namespace ui {
 
 class X11HotplugEventHandler;
 class XScopedEventSelector;
 
 // Responsible for notifying X11EventSource when new XEvents are available and
 // processing/dispatching XEvents. Implementations will likely be a
 // PlatformEventSource.
 class X11EventSourceDelegate {
  public:
@@ skipping 39 matching lines @@
 
   void BlockUntilWindowUnmapped(XID window);
 
   XDisplay* display() { return display_; }
 
   // Returns the timestamp of the event currently being dispatched.  Falls back
   // on GetCurrentServerTime() if there's no event being dispatched, or if the
   // current event does not have a timestamp.
   Time GetTimestamp();
 
+  // Returns the root pointer location only if there is an event being
+  // dispatched that contains that information.
+  base::Optional<gfx::Point> GetRootCursorLocationFromCurrentEvent() const;
+
   void StopCurrentEventStream();
   void OnDispatcherListChanged();
 
  protected:
   // Extracts cookie data from |xevent| if it's of GenericType, and dispatches
   // the event. This function also frees up the cookie data after dispatch is
   // complete.
   void ExtractCookieDataDispatchEvent(XEvent* xevent);
 
   // Handles updates after event has been dispatched.
   void PostDispatchEvent(XEvent* xevent);
 
   // Block until receiving a structure notify event of |type| on |window|.
   // Dispatch all encountered events prior to the one we're blocking on.
   void BlockOnWindowStructureEvent(XID window, int type);
 
   // Explicitly asks the X11 server for the current timestamp, and updates
   // |last_seen_server_time_| with this value.
   Time GetCurrentServerTime();
 
  private:
   static X11EventSource* instance_;
 
   X11EventSourceDelegate* delegate_;
 
   // The connection to the X11 server used to receive the events.
   XDisplay* display_;
 
-  // The timestamp of the event being dispatched.
-  Time event_timestamp_;
+  // Events currently being dispatched.  The topmost event in this stack
+  // corresponds to the deepest-nested message loop.
+  std::stack<XEvent*> dispatching_events_;
 
   // State necessary for UpdateLastSeenServerTime
   bool dummy_initialized_;
   XWindow dummy_window_;
   XAtom dummy_atom_;
   std::unique_ptr<XScopedEventSelector> dummy_window_events_;
 
   // Keeps track of whether this source should continue to dispatch all the
   // available events.
   bool continue_stream_ = true;
 
   std::unique_ptr<X11HotplugEventHandler> hotplug_event_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(X11EventSource);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_PLATFORM_X11_X11_EVENT_SOURCE_H_