[CRD iOS] Viewport fling animation

remoting/client/fling_animation.cc

+// Copyright 2017 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 "remoting/client/fling_animation.h"
+
+namespace remoting {
+
+FlingAnimation::FlingAnimation(float time_constant,

[nicholss, 2017/05/10 19:34:05]

It seems like FlingTracker could be just a core class inside of FlingAnimation,
what is the value of having them separate?

[Yuwei, 2017/05/10 23:28:24]

TBH I'm not sure :)
I'm just slightly against putting together modules that are not so dependent
with each other. By separating them, we will be able to swap for another
FlingTracker or unittest them independently, although we are not doing either or
them now...

+                               const FlingCallback& fling_callback)
+    : fling_tracker_(time_constant), fling_callback_(fling_callback) {}

[nicholss, 2017/05/10 19:34:05]

I am not sure this would compile, how is a float assigned to a fling_tracker?

RE: fling_tracker_(time_constant)

[Yuwei, 2017/05/10 23:28:24]

This is essentially calling the FlingTracker(time_constant) constructor.

However you did remind me that I forgot to mark the constructor as `explicit` :P
Without `explicit` I can do conversion like:

FlingTracker tracker_ = 100.f;

Which doesn't make sense :)

+
+FlingAnimation::~FlingAnimation() {}
+
+void FlingAnimation::Reset(float velocity_x, float velocity_y) {
+  previous_position_x_ = 0.f;
+  previous_position_y_ = 0.f;
+  fling_tracker_.StartFling(velocity_x, velocity_y);
+}
+
+bool FlingAnimation::IsAnimationInProgress() const {
+  return fling_tracker_.IsFlingInProgress();
+}
+
+void FlingAnimation::Tick() {
+  float x, y;
+  bool in_progress =
+      fling_tracker_.TrackPositions(base::TimeTicks::Now(), &x, &y);

[nicholss, 2017/05/10 19:34:05]

If this returned deltas you would not need to know about the previous position. 

[Yuwei, 2017/05/10 23:28:24]

Done.

+  if (in_progress) {
+    fling_callback_.Run(x - previous_position_x_, y - previous_position_y_);
+    previous_position_x_ = x;
+    previous_position_y_ = y;
+  }
+}
+
+void FlingAnimation::Abort() {
+  fling_tracker_.StopFling();
+}
+
+}  // namespace remoting