[Android] Introduce state machine in stylus text selection

content/browser/renderer_host/input/stylus_text_selector.cc

 // 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.
 
 #include "content/browser/renderer_host/input/stylus_text_selector.h"
 
 #include "ui/events/event_constants.h"
 #include "ui/events/gesture_detection/gesture_detector.h"
 #include "ui/events/gesture_detection/gesture_provider_config_helper.h"
 #include "ui/events/gesture_detection/motion_event.h"
@@ skipping 21 matching lines @@
 
   return detector;
 }
 
 }  // namespace
 
 StylusTextSelector::StylusTextSelector(StylusTextSelectorClient* client)
     : client_(client),
       text_selection_triggered_(false),
       secondary_button_pressed_(false),
-      dragging_(false),
-      dragged_(false),
+      drag_state_(NO_DRAG),
       anchor_x_(0.0f),
       anchor_y_(0.0f) {
   DCHECK(client);
 }
 
 StylusTextSelector::~StylusTextSelector() {
 }
 
 bool StylusTextSelector::OnTouchEvent(const MotionEvent& event) {
   // Only trigger selection on ACTION_DOWN to prevent partial touch or gesture
   // sequences from being forwarded.
   if (event.GetAction() == MotionEvent::ACTION_DOWN)
     text_selection_triggered_ = ShouldStartTextSelection(event);
 
   if (!text_selection_triggered_)
     return false;
 
   secondary_button_pressed_ =
       event.GetButtonState() == MotionEvent::BUTTON_SECONDARY;
 
   switch (event.GetAction()) {
     case MotionEvent::ACTION_DOWN:
-      dragging_ = false;
-      dragged_ = false;
+      drag_state_ = NO_DRAG;
       anchor_x_ = event.GetX();
       anchor_y_ = event.GetY();
       break;
 
     case MotionEvent::ACTION_MOVE:
       if (!secondary_button_pressed_) {
-        dragging_ = false;
+        drag_state_ =

[aelias_OOO_until_Jul13, 2017/05/17 20:54:23]

Clearer to write this as:

if (drag_state_ == DRAGGING_IN_PROGRESS)
  drag_state_ = WAS_DRAGGED;

[AKVT, 2017/05/18 10:12:19]

Done.

+            (drag_state_ == DRAGGING_IN_PROGRESS || drag_state_ == WAS_DRAGGED)
+                ? WAS_DRAGGED
+                : NO_DRAG;
         anchor_x_ = event.GetX();
         anchor_y_ = event.GetY();
       }
       break;
 
     case MotionEvent::ACTION_UP:
     case MotionEvent::ACTION_CANCEL:
-      if (dragged_)
+      if (drag_state_ == DRAGGING_IN_PROGRESS || drag_state_ == WAS_DRAGGED)
         client_->OnStylusSelectEnd();
-      dragged_ = false;
-      dragging_ = false;
+      drag_state_ = NO_DRAG;
       break;
 
     case MotionEvent::ACTION_POINTER_UP:
     case MotionEvent::ACTION_POINTER_DOWN:
       break;
     case MotionEvent::ACTION_NONE:
     case MotionEvent::ACTION_HOVER_ENTER:
     case MotionEvent::ACTION_HOVER_EXIT:
     case MotionEvent::ACTION_HOVER_MOVE:
     case MotionEvent::ACTION_BUTTON_PRESS:
     case MotionEvent::ACTION_BUTTON_RELEASE:
       NOTREACHED();
       break;
   }
 
   if (!gesture_detector_)
     gesture_detector_ = CreateGestureDetector(this);
 
   gesture_detector_->OnTouchEvent(event);
 
   // Always return true, even if |gesture_detector_| technically doesn't
   // consume the event. This prevents forwarding of a partial touch stream.
   return true;
 }
 
 bool StylusTextSelector::OnSingleTapUp(const MotionEvent& e, int tap_count) {
   DCHECK(text_selection_triggered_);
-  DCHECK(!dragging_);
+  DCHECK(drag_state_ == NO_DRAG);

[aelias_OOO_until_Jul13, 2017/05/17 20:54:23]

This isn't equivalent to the previous behavior, I suggest:

DCHECK_NE(DRAGGING_IN_PROGRESS, drag_state_);

[AKVT, 2017/05/18 10:12:19]

Done.

   client_->OnStylusSelectTap(e.GetEventTime(), e.GetX(), e.GetY());
   return true;
 }
 
 bool StylusTextSelector::OnScroll(const MotionEvent& e1,
                                   const MotionEvent& e2,
                                   const MotionEvent& secondary_pointer_down,
                                   float distance_x,
                                   float distance_y) {
   DCHECK(text_selection_triggered_);
 
   // Return if Stylus button is not pressed.
   if (!secondary_button_pressed_)
     return true;
 
-  if (!dragging_) {
-    dragging_ = true;
-    dragged_ = true;
+  if (drag_state_ == NO_DRAG || drag_state_ == WAS_DRAGGED) {
+    drag_state_ = DRAGGING_IN_PROGRESS;
     client_->OnStylusSelectBegin(anchor_x_, anchor_y_, e2.GetX(), e2.GetY());
   } else {
     client_->OnStylusSelectUpdate(e2.GetX(), e2.GetY());
   }
 
   return true;
 }
 
 // static
 bool StylusTextSelector::ShouldStartTextSelection(const MotionEvent& event) {
   DCHECK_GT(event.GetPointerCount(), 0u);
   // Currently we are supporting stylus-only cases.
   const bool is_stylus = event.GetToolType(0) == MotionEvent::TOOL_TYPE_STYLUS;
   const bool is_only_secondary_button_pressed =
       event.GetButtonState() == MotionEvent::BUTTON_SECONDARY;
   return is_stylus && is_only_secondary_button_pressed;
 }
 
 }  // namespace content