ui/events/event_targeter.h

   1 // Copyright (c) 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_TARGETER_H_
   6 #define UI_EVENTS_EVENT_TARGETER_H_
   7
   8 #include "base/compiler_specific.h"
   9 #include "ui/events/event.h"
  10 #include "ui/events/events_export.h"
  11
  12 namespace ui {
  13
  14 class Event;
  15 class EventTarget;
  16 class LocatedEvent;
  17
  18 class EVENTS_EXPORT EventTargeter {
  19  public:
  20   virtual ~EventTargeter();
  21
  22   // Returns the target |event| should be dispatched to. If there is no such
  23   // target, return NULL. If |event| is a located event, the location of |event|
  24   // is in the coordinate space of |root|. Furthermore, the targeter can mutate
  25   // the event (e.g., by changing the location of the event to be in the
  26   // returned target's coordinate space) so that it can be dispatched to the
  27   // target without any further modification.
  28   virtual EventTarget* FindTargetForEvent(EventTarget* root,
  29                                           Event* event);
  30
  31   // Same as FindTargetForEvent(), but used for positional events. The location
  32   // etc. of |event| are in |root|'s coordinate system. When finding the target
  33   // for the event, the targeter can mutate the |event| (e.g. change the
  34   // coordinate to be in the returned target's coordinate system) so that it can
  35   // be dispatched to the target without any further modification.
  36   // TODO(tdanderson|sadrul): This should not be in the public API of
  37   //                          EventTargeter.
  38   virtual EventTarget* FindTargetForLocatedEvent(EventTarget* root,
  39                                                  LocatedEvent* event);
  40
  41   // Returns true if |target| or one of its descendants can be a target of
  42   // |event|. This requires that |target| and its descendants are not
  43   // prohibited from accepting the event, and that the event is within an
  44   // actionable region of the target's bounds. Note that the location etc. of
  45   // |event| is in |target|'s parent's coordinate system.
  46   // TODO(tdanderson|sadrul): This function should be made non-virtual and
  47   //                          non-public.
  48   virtual bool SubtreeShouldBeExploredForEvent(EventTarget* target,
  49                                                const LocatedEvent& event);
  50
  51   // Returns the next best target for |event| as compared to |previous_target|.
  52   // |event| is in the local coordinate space of |previous_target|.
  53   // Also mutates |event| so that it can be dispatched to the returned target
  54   // (e.g., by changing |event|'s location to be in the returned target's
  55   // coordinate space).
  56   virtual EventTarget* FindNextBestTarget(EventTarget* previous_target,
  57                                           Event* event);
  58
  59  protected:
  60   // Returns false if neither |target| nor any of its descendants are allowed
  61   // to accept |event| for reasons unrelated to the event's location or the
  62   // target's bounds. For example, overrides of this function may consider
  63   // attributes such as the visibility or enabledness of |target|. Note that
  64   // the location etc. of |event| is in |target|'s parent's coordinate system.
  65   virtual bool SubtreeCanAcceptEvent(EventTarget* target,
  66                                      const LocatedEvent& event) const;
  67
  68   // Returns whether the location of the event is in an actionable region of the
  69   // target. Note that the location etc. of |event| is in the |target|'s
  70   // parent's coordinate system.
  71   virtual bool EventLocationInsideBounds(EventTarget* target,
  72                                          const LocatedEvent& event) const;
  73 };
  74
  75 }  // namespace ui
  76
  77 #endif  // UI_EVENTS_EVENT_TARGETER_H_