ui/events/event_processor.h

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef UI_EVENTS_EVENT_PROCESSOR_H_
   6 #define UI_EVENTS_EVENT_PROCESSOR_H_
   7
   8 #include "ui/events/event_dispatcher.h"
   9 #include "ui/events/event_source.h"
  10
  11 namespace ui {
  12
  13 // EventProcessor receives an event from an EventSource and dispatches it to a
  14 // tree of EventTargets.
  15 class EVENTS_EXPORT EventProcessor : public EventDispatcherDelegate {
  16  public:
  17   ~EventProcessor() override {}
  18
  19   // Returns the root of the tree this event processor owns.
  20   virtual EventTarget* GetRootTarget() = 0;
  21
  22   // Dispatches an event received from the EventSource to the tree of
  23   // EventTargets (whose root is returned by GetRootTarget()).  The co-ordinate
  24   // space of the source must be the same as the root target, except that the
  25   // target may have a high-dpi scale applied.
  26   // TODO(tdanderson|sadrul): This is only virtual for testing purposes. It
  27   //                          should not be virtual at all.
  28   virtual EventDispatchDetails OnEventFromSource(Event* event)
  29       WARN_UNUSED_RESULT;
  30
  31  protected:
  32   // Invoked at the start of processing, before an EventTargeter is used to
  33   // find the target of the event. If processing should not take place, marks
  34   // |event| as handled. Otherwise updates |event| so that the targeter can
  35   // operate correctly (e.g., it can be used to update the location of the
  36   // event when dispatching from an EventSource in high-DPI) and updates any
  37   // members in the event processor as necessary.
  38   virtual void OnEventProcessingStarted(Event* event);
  39
  40   // Invoked when the processing of |event| has finished (i.e., when no further
  41   // dispatching of |event| will be performed by this EventProcessor). Note
  42   // that the last target to which |event| was dispatched may have been
  43   // destroyed.
  44   virtual void OnEventProcessingFinished(Event* event);
  45 };
  46
  47 }  // namespace ui
  48
  49 #endif  // UI_EVENTS_EVENT_PROCESSOR_H_