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, this should return NULL.
  24   virtual EventTarget* FindTargetForEvent(EventTarget* root,
  25                                           Event* event);
  26
  27   // Same as FindTargetForEvent(), but used for positional events. The location
  28   // etc. of |event| are in |root|'s coordinate system. When finding the target
  29   // for the event, the targeter can mutate the |event| (e.g. change the
  30   // coordinate to be in the returned target's coordinate system) so that it can
  31   // be dispatched to the target without any farther modification.
  32   virtual EventTarget* FindTargetForLocatedEvent(EventTarget* root,
  33                                                  LocatedEvent* event);
  34
  35   // Returns true if |target| or one of its descendants can be a target of
  36   // |event|. This requires that |target| and its descendants are not
  37   // prohibited from accepting the event, and that the event is within an
  38   // actionable region of the target's bounds. Note that the location etc. of
  39   // |event| is in |target|'s parent's coordinate system.
  40   // TODO(tdanderson|sadrul): This function should be made non-virtual and
  41   //                          non-public.
  42   virtual bool SubtreeShouldBeExploredForEvent(EventTarget* target,
  43                                                const LocatedEvent& event);
  44
  45   // Returns the next best target for |event| as compared to |previous_target|.
  46   // Also mutates |event| so that it can be dispatched to the returned target
  47   // (e.g., by changing |event|'s location to be in the returned target's
  48   // coordinate space).
  49   virtual EventTarget* FindNextBestTarget(EventTarget* previous_target,
  50                                           Event* event);
  51
  52  protected:
  53   // Returns false if neither |target| nor any of its descendants are allowed
  54   // to accept |event| for reasons unrelated to the event's location or the
  55   // target's bounds. For example, overrides of this function may consider
  56   // attributes such as the visibility or enabledness of |target|. Note that
  57   // the location etc. of |event| is in |target|'s parent's coordinate system.
  58   virtual bool SubtreeCanAcceptEvent(EventTarget* target,
  59                                      const LocatedEvent& event) const;
  60
  61   // Returns whether the location of the event is in an actionable region of the
  62   // target. Note that the location etc. of |event| is in the |target|'s
  63   // parent's coordinate system.
  64   virtual bool EventLocationInsideBounds(EventTarget* target,
  65                                          const LocatedEvent& event) const;
  66 };
  67
  68 }  // namespace ui
  69
  70 #endif  // UI_EVENTS_EVENT_TARGETER_H_