Add support for calculating the position of the top controls in the cc layer.

cc/top_controls_animation.cc

+// 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.
+
+#include "cc/top_controls_animation.h"
+
+#include "base/logging.h"
+#include "cc/timing_function.h"
+
+using base::TimeDelta;
+using base::TimeTicks;
+
+namespace cc {
+
+scoped_ptr<TopControlsAnimation> TopControlsAnimation::create(
+    float startScrollOffset,
+    float topControlsHeight,
+    TimeTicks startTime,
+    TimeDelta maxDuration) {
+  return make_scoped_ptr(new TopControlsAnimation(
+      startScrollOffset, topControlsHeight, startTime, maxDuration));
+}
+
+TopControlsAnimation::TopControlsAnimation(float startScrollOffset,
+                                           float topControlsHeight,
+                                           TimeTicks startTime,
+                                           TimeDelta maxDuration)
+    : start_scroll_offset_(startScrollOffset),
+      top_controls_height_(topControlsHeight),
+      direction_(1),
+      start_time_(startTime),
+      max_duration_(maxDuration) {
+  timing_function_ = EaseTimingFunction::create();
+}
+
+TopControlsAnimation::~TopControlsAnimation() {
+}
+
+void TopControlsAnimation::setDirection(bool showing) {
+  direction_ = showing ? 1 : -1;
+}
+
+float TopControlsAnimation::scrollOffsetAtTime(TimeTicks time) const {
+  TimeDelta elapsed_time = time - start_time_;
+  float offsetDelta = timing_function_->getValue(
+      elapsed_time.InSecondsF() / max_duration_.InSecondsF())
+          * direction_ * top_controls_height_;
+  return start_scroll_offset_ + offsetDelta;
+}
+
+bool TopControlsAnimation::isAnimationCompleteAtTime(TimeTicks time) const {
+  float scrollOffset = scrollOffsetAtTime(time);
+  if (direction_ == 1)
+    return scrollOffset >= 0;
+  else
+    return scrollOffset <= -top_controls_height_;

[aelias_OOO_until_Jul13, 2012/12/19 08:31:18]

It would be simpler to just compare max_duration_ to time here.

[Ted C, 2012/12/19 21:34:17]

I'd prefer to keep it comparing against expected height as it will terminate
earlier.  The max_duration is often longer than the animation will run as the
max duration is how long the animation could take if it needed to height or show
the full height, which it is often not doing.

+}
+
+}  // namespace cc