Simplify HomeCardGestureManager::UpdateScrollState()

athena/home/home_card_gesture_manager.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 ATHENA_HOME_HOME_CARD_GESTURE_MANAGER_H_
 #define ATHENA_HOME_HOME_CARD_GESTURE_MANAGER_H_
 
 #include "athena/home/public/home_card.h"
 #include "athena/athena_export.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace ui {
 class GestureEvent;
 }
 
 namespace athena {
 
 // Handles the touch gestures over the home card.
 class ATHENA_EXPORT HomeCardGestureManager {
  public:
   class Delegate {
    public:
     // Called when the gesture has ended. The state of the home card will
     // end up with |final_state|.
     virtual void OnGestureEnded(HomeCard::State final_state) = 0;
 
-    // Called when the gesture position is updated so that |delegate| should
-    // update the visual. The arguments represent the state of the current
-    // gesture position is switching from |from_state| to |to_state|, and
-    // the level of the progress is at |progress|, which is 0 to 1.
-    // |from_state| and |to_state| could be same. For example, if the user moves
-    // the finger down to the bottom of the screen, both states are MINIMIZED.
-    // In that case |progress| is 0.
+    // Called when the gesture position is updated so that |delegate| updates
+    // the visual. The arguments indicate that the gesture is switching from
+    // |from_state| to |to_state|, and that the level of progress is at
+    // |progress|, which is 0 to 1.
+    // |from_state| may be equal to |to_state| but only if

[Jun Mukai, 2014/09/02 03:51:42]

I think from_state could be equal to to_state and CENTERED when the user drag-up
from CENTERED state.

[pkotwicz, 2014/09/02 04:41:32]

With the current implementation of UpdateScrollState(), it does not seem
possible for both |from_state| and |to_state| to be CENTERED. Note line 97 in
home_card_gesture_manager.cc
VISIBLE_MINIMIZED > VISIBLE_BOTTOM > VISIBLE_CENTERED > HIDDEN

+    // |from_state| == VISIBLE_MINIMIZED. This occurs if the user moves their
+    // finger to the bottom of the screen.
     virtual void OnGestureProgressed(
         HomeCard::State from_state,
         HomeCard::State to_state,
         float progress) = 0;
   };
 
   HomeCardGestureManager(Delegate* delegate,
                          const gfx::Rect& screen_bounds);
   ~HomeCardGestureManager();
 
@@ skipping 18 matching lines @@
 
   // The bounds of the screen to compute the home card bounds.
   gfx::Rect screen_bounds_;
 
   DISALLOW_COPY_AND_ASSIGN(HomeCardGestureManager);
 };
 
 }  // namespace athena
 
 #endif  // ATHENA_HOME_HOME_CARD_GESTURE_MANAGER_H_