cros: Laser pointer fades out on release, do not cover palette.

ash/laser/laser_pointer_points.h

 // Copyright 2016 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 ASH_LASER_LASER_POINTER_POINTS_H_
 #define ASH_LASER_LASER_POINTER_POINTS_H_
 
 #include <deque>
 #include <memory>
 
 #include "ash/ash_export.h"
 #include "base/time/time.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace ash {
 
 // LaserPointerPoints is a helper class used for displaying the palette tool
 // laser pointer. It keeps track of the points needed to render the laser
 // pointer and its tail.
 class ASH_EXPORT LaserPointerPoints {
  public:
   // Struct to describe each point.
   struct LaserPoint {
     gfx::Point location;
     base::Time creation_time;

[jdufault, 2016/10/04 22:04:13]

Why does the point store its creation_time? age can be computed relative to
collection_latest_time_.

[sammiequon, 2016/10/05 17:42:23]

Done.

+    // age is a value between [0,1] where 0 means the point was just added and 1
+    // means that the point is just about to be removed.
+    double age;
   };
 
   // Constructor with a parameter to choose the fade out time of the points in
   // the collection.
   explicit LaserPointerPoints(base::TimeDelta life_duration);
   ~LaserPointerPoints();
 
   // Adds a point. Automatically clears points that are too old.
   void AddPoint(const gfx::Point& point);
+  // Updates the collection latest time. Automatically clears points that are
+  // too old.
+  void MoveForwardToCurrentTime();
+  void MoveForwardToTime(const base::Time& new_latest_time);
   // Removes all points.
   void Clear();
   // Gets the bounding box of the points.
   gfx::Rect GetBoundingBox();
   // Returns the oldest point in the collection.
   LaserPoint GetOldest() const;
   // Returns the newest point in the collection.
   LaserPoint GetNewest() const;
   // Returns the number of points in the collection.
   int GetNumberOfPoints() const;
   // Whether there are any points or not.
   bool IsEmpty() const;
   // Expose the collection so callers can work with the points.
   const std::deque<LaserPoint>& laser_points();
 
  private:
   friend class LaserPointerPointsTestApi;
 
   void ClearOldPoints();
+  void UpdateAges();
 
   base::TimeDelta life_duration_;
   std::deque<LaserPoint> points_;
+  // The latest time of the collection of points. This gets updated when new
+  // points are added or when MoveForwardInTime is called.
+  base::Time collection_latest_time_;
 
   DISALLOW_COPY_AND_ASSIGN(LaserPointerPoints);
 };
 
 }  // namespace ash
 
 #endif  // ASH_LASER_LASER_POINTER_POINTS_H_