[Android] Support double-tap selection

ui/events/gesture_detection/gesture_detector.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_GESTURE_DETECTION_GESTURE_DETECTOR_H_
 #define UI_EVENTS_GESTURE_DETECTION_GESTURE_DETECTOR_H_
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "ui/events/gesture_detection/gesture_detection_export.h"
@@ skipping 51 matching lines @@
     // Whether |OnTwoFingerTap| should be called for two finger tap
     // gestures. Defaults to false.
     bool two_finger_tap_enabled;
 
     // Maximum distance between pointers for a two finger tap.
     float two_finger_tap_max_separation;
 
     // Maximum time the second pointer can be active for a two finger tap.
     base::TimeDelta two_finger_tap_timeout;
 
+    // Single tap count repetition length. Defaults to 1 (no repetition count).
+    // Note that when double-tap detection is enabled, the single tap repeat
+    // count will always be 1.
+    int single_tap_repeat_length;
+
     VelocityTracker::Strategy velocity_tracker_strategy;
   };
 
   GestureDetector(const Config& config,
                   GestureListener* listener,
                   DoubleTapListener* optional_double_tap_listener);
   ~GestureDetector();
 
   bool OnTouchEvent(const MotionEvent& ev);
 
@@ skipping 45 matching lines @@
   bool two_finger_tap_allowed_for_gesture_;
 
   scoped_ptr<MotionEvent> current_down_event_;
   scoped_ptr<MotionEvent> previous_up_event_;
   scoped_ptr<MotionEvent> secondary_pointer_down_event_;
 
   // True when the user is still touching for the second tap (down, move, and
   // up events). Can only be true if there is a double tap listener attached.
   bool is_double_tapping_;
 
+  int single_tap_count_;

[tdresser, 2015/09/23 14:10:46]

The semantics of this variable feel a bit confusing.
Would it be clearer if this was the number of taps that have already happened
during the current tap sequence, instead of the tap count of the next tap to
occur?

[jdduke (slow), 2015/09/23 19:56:04]

Yeah, though I think we'll need an auxiliary variable to indicate that the
current touch sequence is possibly a repeated one (the IsConsideredDoubleTap
check needs to happen on DOWN for several reasons).

[tdresser, 2015/09/24 12:05:00]

Thanks - I find this easier to follow.

+  int single_tap_repeat_length_;
+
   float last_focus_x_;
   float last_focus_y_;
   float down_focus_x_;
   float down_focus_y_;
 
   bool longpress_enabled_;
   bool showpress_enabled_;
   bool swipe_enabled_;
   bool two_finger_tap_enabled_;
 
   // Determines speed during touch scrolling.
   VelocityTrackerState velocity_tracker_;
 
   DISALLOW_COPY_AND_ASSIGN(GestureDetector);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_GESTURE_DETECTION_GESTURE_DETECTOR_H_