Suppress scrollbar animation if the scroll gesture does not scroll

cc/animation/scrollbar_animation_controller_linear_fade.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/animation/scrollbar_animation_controller_linear_fade.h"
 
 #include "base/time/time.h"
 #include "cc/layers/layer_impl.h"
 
 namespace cc {
 
 scoped_ptr<ScrollbarAnimationControllerLinearFade>
 ScrollbarAnimationControllerLinearFade::Create(LayerImpl* scroll_layer,
                                                base::TimeDelta fadeout_delay,
                                                base::TimeDelta fadeout_length) {
   return make_scoped_ptr(new ScrollbarAnimationControllerLinearFade(
       scroll_layer, fadeout_delay, fadeout_length));
 }
 
 ScrollbarAnimationControllerLinearFade::ScrollbarAnimationControllerLinearFade(
     LayerImpl* scroll_layer,
     base::TimeDelta fadeout_delay,
     base::TimeDelta fadeout_length)
     : ScrollbarAnimationController(),
       scroll_layer_(scroll_layer),
       scroll_gesture_in_progress_(false),
+      scroll_gesture_has_scrolled_(false),
       fadeout_delay_(fadeout_delay),
       fadeout_length_(fadeout_length) {}
 
 ScrollbarAnimationControllerLinearFade::
     ~ScrollbarAnimationControllerLinearFade() {}
 
-bool ScrollbarAnimationControllerLinearFade::IsScrollGestureInProgress() const {
-  return scroll_gesture_in_progress_;
-}
-
 bool ScrollbarAnimationControllerLinearFade::IsAnimating() const {
   return !last_awaken_time_.is_null();
 }
 
 base::TimeDelta ScrollbarAnimationControllerLinearFade::DelayBeforeStart(
     base::TimeTicks now) const {
   if (now > last_awaken_time_ + fadeout_delay_)
     return base::TimeDelta();
   return fadeout_delay_ - (now - last_awaken_time_);
 }
 
 bool ScrollbarAnimationControllerLinearFade::Animate(base::TimeTicks now) {
   float opacity = OpacityAtTime(now);
   scroll_layer_->SetScrollbarOpacity(opacity);
   if (!opacity)
     last_awaken_time_ = base::TimeTicks();
   return IsAnimating() && DelayBeforeStart(now) == base::TimeDelta();
 }
 
 void ScrollbarAnimationControllerLinearFade::DidScrollGestureBegin() {
-  scroll_layer_->SetScrollbarOpacity(1.0f);
   scroll_gesture_in_progress_ = true;
-  last_awaken_time_ = base::TimeTicks();
+  scroll_gesture_has_scrolled_ = false;
 }
 
 void ScrollbarAnimationControllerLinearFade::DidScrollGestureEnd(
     base::TimeTicks now) {
+  // The animation should not be triggered if no scrolling has occurred.
+  if (scroll_gesture_has_scrolled_)
+    last_awaken_time_ = now;
+  scroll_gesture_has_scrolled_ = false;
   scroll_gesture_in_progress_ = false;
-  last_awaken_time_ = now;
 }
 
-void ScrollbarAnimationControllerLinearFade::DidProgrammaticallyUpdateScroll(
+void ScrollbarAnimationControllerLinearFade::DidScrollUpdate(
     base::TimeTicks now) {
-  // Don't set scroll_gesture_in_progress_ as this scroll is not from a gesture
-  // and we won't receive ScrollEnd.
   scroll_layer_->SetScrollbarOpacity(1.0f);
-  last_awaken_time_ = now;
+  // The animation should only be activated if the scroll updated occurred
+  // programatically, outside the scope of a scroll gesture.
+  if (scroll_gesture_in_progress_) {
+    last_awaken_time_ = base::TimeTicks();
+    scroll_gesture_has_scrolled_ = true;
+  } else {
+    last_awaken_time_ = now;
+  }
 }
 
 float ScrollbarAnimationControllerLinearFade::OpacityAtTime(
     base::TimeTicks now) {
-  if (scroll_gesture_in_progress_)
+  if (scroll_gesture_has_scrolled_)
     return 1.0f;
 
   if (last_awaken_time_.is_null())
     return 0.0f;
 
   base::TimeDelta delta = now - last_awaken_time_;
 
   if (delta <= fadeout_delay_)
     return 1.0f;
   if (delta < fadeout_delay_ + fadeout_length_) {
     return (fadeout_delay_ + fadeout_length_ - delta).InSecondsF() /
            fadeout_length_.InSecondsF();
   }
   return 0.0f;
 }
 
 }  // namespace cc