Overlay scrollbars expand only when mouse is near thumb

cc/input/scrollbar_animation_controller.h

 // Copyright 2012 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 CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_
 #define CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_
 
 #include "base/cancelable_callback.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
@@ skipping 64 matching lines @@
   // DidResize expects to be called when clip layer size changed or scroll layer
   // size changed.
   void DidResize();
 
   void DidScrollBegin();
   void DidScrollEnd();
 
   void DidMouseDown();
   void DidMouseUp();
   void DidMouseLeave();
-  void DidMouseMoveNear(ScrollbarOrientation, float);
+  void DidMouseMove(const gfx::PointF& device_viewport_point);
 
   // Called when Blink wants to show the scrollbars (via
   // ScrollableArea::showOverlayScrollbars).
   void DidRequestShowFromMainThread();
 
-  bool MouseIsOverScrollbar(ScrollbarOrientation orientation) const;
+  bool MouseIsOverScrollbarThumb(ScrollbarOrientation orientation) const;
+  bool MouseIsNearScrollbarThumb(ScrollbarOrientation orientation) const;
   bool MouseIsNearScrollbar(ScrollbarOrientation orientation) const;
   bool MouseIsNearAnyScrollbar() const;
 
   static constexpr float kMouseMoveDistanceToTriggerFadeIn = 30.0f;
 
  private:
   // Describes whether the current animation should FadeIn or FadeOut.
   enum AnimationChange { NONE, FADE_IN, FADE_OUT };
 
   ScrollbarAnimationController(ElementId scroll_element_id,
                                ScrollbarAnimationControllerClient* client,
                                base::TimeDelta fade_delay,
                                base::TimeDelta fade_out_resize_delay,
                                base::TimeDelta fade_duration);
 
   ScrollbarAnimationController(ElementId scroll_element_id,
                                ScrollbarAnimationControllerClient* client,
                                base::TimeDelta fade_delay,
                                base::TimeDelta fade_out_resize_delay,
                                base::TimeDelta fade_duration,
                                base::TimeDelta thinning_duration);
 
   ScrollbarSet Scrollbars() const;
+  ScrollbarLayerImplBase* GetScrollbar(ScrollbarOrientation orientation) const;
   SingleScrollbarAnimationControllerThinning& GetScrollbarAnimationController(
       ScrollbarOrientation) const;
 
   // Returns how far through the animation we are as a progress value from
   // 0 to 1.
   float AnimationProgressAtTime(base::TimeTicks now);
   void RunAnimationFrame(float progress);
 
   void StartAnimation();
   void StopAnimation();
 
   void Show();
 
   void PostDelayedAnimation(AnimationChange animation_change, bool on_resize);
 
   bool Captured() const;
 
-  bool CalcNeedTriggerScrollbarShow(ScrollbarOrientation orientation,
-                                    float distance) const;
-
   void ApplyOpacityToScrollbars(float opacity);
 
   ScrollbarAnimationControllerClient* client_;
 
   base::TimeTicks last_awaken_time_;
 
   base::TimeDelta fade_delay_;
   base::TimeDelta fade_out_resize_delay_;
 
   base::TimeDelta fade_duration_;
 
-  bool need_trigger_scrollbar_show_;
+  bool need_trigger_scrollbar_fade_in_;
 
   bool is_animating_;
   AnimationChange animation_change_;
 
   const ElementId scroll_element_id_;
   bool currently_scrolling_;
   bool show_in_fast_scroll_;
 
   base::CancelableClosure delayed_scrollbar_animation_;
 
   float opacity_;
 
   const bool show_scrollbars_on_scroll_gesture_;
   const bool need_thinning_animation_;
+
   std::unique_ptr<SingleScrollbarAnimationControllerThinning>
-      vertical_controller_;
-  std::unique_ptr<SingleScrollbarAnimationControllerThinning>
-      horizontal_controller_;
+      scrollbar_controllers_[2];

[bokan, 2017/04/28 14:15:17]

Please keep these as vertical_controller_ and horizontal_controller_. IMO,
having `for` loops to do something for both controllers ends up being less
readable and, in most cases, doesn't save us from any code copying. For cases
where you want to do something based on ScrollbarOrientation, you can keep the
helper return the correct controller.

+
+  bool mouse_is_near_scrollbar_[2];

[bokan, 2017/04/28 14:15:17]

Lets move this into the thinning controller, pass the actual point in
DidMoveMouse, and calculate "is near/over track/thumb" inside the individual
controller. Then this class can just ask the Thinning controllers for the
current mouse<->scrollbar state.

The "Thinning" controller should really be an "IndividualScrollbar" controller,
but we can rename later. The point being that ThinningController manages state
for each individual scrollbar. That way the code becomes more natural as you
don't have to duplicate the Vertical/Horizontal split in this class more than
once.

 
   base::WeakPtrFactory<ScrollbarAnimationController> weak_factory_;
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_