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

ash/laser/laser_pointer_points.cc

 // 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.
 
 #include "ash/laser/laser_pointer_points.h"
 
 #include <algorithm>
 #include <limits>
 
 namespace ash {
+namespace {
+
+double NormalizedValue(double initial_value,
+                       double final_value,
+                       double current_value) {
+  double computed =
+      (current_value - initial_value) / (final_value - initial_value);
+  return std::min(1.0, std::max(computed, 0.0));
+}
+}
 
 LaserPointerPoints::LaserPointerPoints(base::TimeDelta life_duration)
     : life_duration_(life_duration) {}
 
 LaserPointerPoints::~LaserPointerPoints() {}
 
 void LaserPointerPoints::AddPoint(const gfx::Point& point) {
+  base::Time current_time = base::Time::Now();
   LaserPoint new_point;
   new_point.location = point;
-  new_point.creation_time = base::Time::Now();
+  new_point.creation_time = current_time;
+  new_point.age = 0.0;
   points_.push_back(new_point);
+  MoveForwardToTime(current_time);
+}
+
+void LaserPointerPoints::MoveForwardToCurrentTime() {
+  MoveForwardToTime(base::Time::Now());
+}
+
+void LaserPointerPoints::MoveForwardToTime(const base::Time& new_latest_time) {
+  collection_latest_time_ = new_latest_time;
   ClearOldPoints();
+  UpdateAges();

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

What about doing something like this?

  auto delta = new_latest_time - collection_latest_time_;
  float lifespan_change = delta / life_duration_;
  for (auto& point : points_)
    point.age -= lifespan_change;

  ClearOldPoints();

ClearOldPoints can also be simplified to check if the age <= 0.

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

Done.

 }
 
 void LaserPointerPoints::Clear() {
   points_.clear();
 }
 
 gfx::Rect LaserPointerPoints::GetBoundingBox() {
   if (IsEmpty())
     return gfx::Rect();
 
@@ skipping 23 matching lines @@
 int LaserPointerPoints::GetNumberOfPoints() const {
   return points_.size();
 }
 
 const std::deque<LaserPointerPoints::LaserPoint>&
 LaserPointerPoints::laser_points() {
   return points_;
 }
 
 void LaserPointerPoints::ClearOldPoints() {
-  DCHECK(!IsEmpty());
   auto first_alive_point =
       std::find_if(points_.begin(), points_.end(), [this](LaserPoint& p) {
-        return GetNewest().creation_time - p.creation_time < life_duration_;
+        return collection_latest_time_ - p.creation_time < life_duration_;
       });
   points_.erase(points_.begin(), first_alive_point);
 }
 
+void LaserPointerPoints::UpdateAges() {
+  std::for_each(points_.begin(), points_.end(), [this](LaserPoint& p) {
+    p.age = 1.0f - NormalizedValue(
+                       (collection_latest_time_ - life_duration_).ToJsTime(),
+                       collection_latest_time_.ToJsTime(),
+                       p.creation_time.ToJsTime());
+  });
+}
 }  // namespace ash