event_processor.h revision 1320f92c476a1ad9d19dba2a48c72b75566198e9 
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
11namespace ui {
12
13// EventProcessor receives an event from an EventSource and dispatches it to a
14// tree of EventTargets.
15class EVENTS_EXPORT EventProcessor : public EventDispatcherDelegate {
16 public:
17  virtual ~EventProcessor() {}
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  virtual EventDispatchDetails OnEventFromSource(Event* event)
27      WARN_UNUSED_RESULT;
28
29 protected:
30  // Prepares the event so that it can be dispatched. This is invoked before
31  // an EventTargeter is used to find the target of the event. So this can be
32  // used to update the event so that the targeter can operate correctly (e.g.
33  // it can be used to updated the location of the event when disptaching from
34  // an EventSource in high-DPI).
35  virtual void PrepareEventForDispatch(Event* event);
36
37  // Invoked when the processing of |event| has finished (i.e., when no further
38  // dispatching of |event| will be performed by this EventProcessor). Note
39  // that the last target to which |event| was dispatched may have been
40  // destroyed.
41  virtual void OnEventProcessingFinished(Event* event);
42};
43
44}  // namespace ui
45
46#endif  // UI_EVENTS_EVENT_PROCESSOR_H_
47