Aura Overlay Scrollbars appear when mouse hovers over scroller edge

cc/input/scrollbar_animation_controller.cc

 // Copyright 2014 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/input/scrollbar_animation_controller.h"
 
 #include <algorithm>
 
 #include "base/time/time.h"
 #include "cc/trees/layer_tree_impl.h"
 
+namespace {
+constexpr float kMouseMoveDistanceToTriggerFadeInAnimation = 50.0f;
+}
+
 namespace cc {
 
 std::unique_ptr<ScrollbarAnimationController>
 ScrollbarAnimationController::CreateScrollbarAnimationControllerAndroid(
     int scroll_layer_id,
     ScrollbarAnimationControllerClient* client,
-    base::TimeDelta delay_before_starting,
-    base::TimeDelta resize_delay_before_starting,
-    base::TimeDelta fade_duration) {
+    base::TimeDelta fade_out_delay,
+    base::TimeDelta fade_out_resize_delay,
+    base::TimeDelta fade_out_duration) {
   return base::WrapUnique(new ScrollbarAnimationController(
-      scroll_layer_id, client, delay_before_starting,
-      resize_delay_before_starting, fade_duration));
+      scroll_layer_id, client, fade_out_delay, fade_out_resize_delay,
+      fade_out_duration));
 }
 
 std::unique_ptr<ScrollbarAnimationController>
 ScrollbarAnimationController::CreateScrollbarAnimationControllerAuraOverlay(
     int scroll_layer_id,
     ScrollbarAnimationControllerClient* client,
-    base::TimeDelta delay_before_starting,
-    base::TimeDelta resize_delay_before_starting,
-    base::TimeDelta fade_duration,
+    base::TimeDelta fade_in_delay,
+    base::TimeDelta fade_out_delay,
+    base::TimeDelta fade_out_resize_delay,
+    base::TimeDelta fade_out_duration,
     base::TimeDelta thinning_duration) {
   return base::WrapUnique(new ScrollbarAnimationController(
-      scroll_layer_id, client, delay_before_starting,
-      resize_delay_before_starting, fade_duration, thinning_duration));
+      scroll_layer_id, client, fade_in_delay, fade_out_delay,
+      fade_out_resize_delay, fade_out_duration, thinning_duration));
 }
 
 ScrollbarAnimationController::ScrollbarAnimationController(
     int scroll_layer_id,
     ScrollbarAnimationControllerClient* client,
-    base::TimeDelta delay_before_starting,
-    base::TimeDelta resize_delay_before_starting,
-    base::TimeDelta fade_duration)
+    base::TimeDelta fade_out_delay,
+    base::TimeDelta fade_out_resize_delay,
+    base::TimeDelta fade_out_duration)
     : client_(client),
-      delay_before_starting_(delay_before_starting),
-      resize_delay_before_starting_(resize_delay_before_starting),
+      fade_out_delay_(fade_out_delay),
+      fade_out_resize_delay_(fade_out_resize_delay),
+      need_trigger_scrollbar_fade_in_(false),
       is_animating_(false),
       scroll_layer_id_(scroll_layer_id),
       currently_scrolling_(false),
       scroll_gesture_has_scrolled_(false),
       opacity_(0.0f),
-      fade_duration_(fade_duration),
+      fade_out_duration_(fade_out_duration),
       need_thinning_animation_(false),
       weak_factory_(this) {
   ApplyOpacityToScrollbars(0.0f);
 }
 
 ScrollbarAnimationController::ScrollbarAnimationController(
     int scroll_layer_id,
     ScrollbarAnimationControllerClient* client,
-    base::TimeDelta delay_before_starting,
-    base::TimeDelta resize_delay_before_starting,
-    base::TimeDelta fade_duration,
+    base::TimeDelta fade_in_delay,
+    base::TimeDelta fade_out_delay,
+    base::TimeDelta fade_out_resize_delay,
+    base::TimeDelta fade_out_duration,
     base::TimeDelta thinning_duration)
     : client_(client),
-      delay_before_starting_(delay_before_starting),
-      resize_delay_before_starting_(resize_delay_before_starting),
+      fade_in_delay_(fade_in_delay),
+      fade_out_delay_(fade_out_delay),
+      fade_out_resize_delay_(fade_out_resize_delay),
+      need_trigger_scrollbar_fade_in_(false),
       is_animating_(false),
       scroll_layer_id_(scroll_layer_id),
       currently_scrolling_(false),
       scroll_gesture_has_scrolled_(false),
       opacity_(0.0f),
-      fade_duration_(fade_duration),
+      fade_out_duration_(fade_out_duration),
       need_thinning_animation_(true),
       weak_factory_(this) {
   vertical_controller_ = SingleScrollbarAnimationControllerThinning::Create(
       scroll_layer_id, ScrollbarOrientation::VERTICAL, client,
       thinning_duration);
   horizontal_controller_ = SingleScrollbarAnimationControllerThinning::Create(
       scroll_layer_id, ScrollbarOrientation::HORIZONTAL, client,
       thinning_duration);
   ApplyOpacityToScrollbars(0.0f);
 }
 
 ScrollbarAnimationController::~ScrollbarAnimationController() {}
 
 ScrollbarSet ScrollbarAnimationController::Scrollbars() const {
   return client_->ScrollbarsFor(scroll_layer_id_);
 }
 
 SingleScrollbarAnimationControllerThinning&
 ScrollbarAnimationController::GetScrollbarAnimationController(
     ScrollbarOrientation orientation) const {
   DCHECK(need_thinning_animation_);
   if (orientation == ScrollbarOrientation::VERTICAL)
     return *(vertical_controller_.get());
   else
     return *(horizontal_controller_.get());
 }
 
 void ScrollbarAnimationController::StartAnimation() {
-  delayed_scrollbar_fade_.Cancel();
+  delayed_scrollbar_fade_in_.Cancel();
+  delayed_scrollbar_fade_out_.Cancel();
   is_animating_ = true;
   last_awaken_time_ = base::TimeTicks();
   client_->SetNeedsAnimateForScrollbarAnimation();
 }
 
 void ScrollbarAnimationController::StopAnimation() {
-  delayed_scrollbar_fade_.Cancel();
+  delayed_scrollbar_fade_in_.Cancel();
+  delayed_scrollbar_fade_out_.Cancel();
   is_animating_ = false;
 }
 
-void ScrollbarAnimationController::PostDelayedAnimationTask(bool on_resize) {
-  base::TimeDelta delay =
-      on_resize ? resize_delay_before_starting_ : delay_before_starting_;
-  delayed_scrollbar_fade_.Reset(
+void ScrollbarAnimationController::PostDelayedFadeIn() {
+  DCHECK(delayed_scrollbar_fade_in_.IsCancelled());

[bokan, 2017/02/28 14:04:49]

It could also be null, right? I don't really care about the fade in task since
we reset it here. My comment was more about ensuring that if we're posting a
fade in, we don't already have a fade out posted.

[chaopeng, 2017/02/28 15:57:20]

CancelableClosure doesnot have is_null(), and its IsCanceled is checking
is_null.
https://cs.chromium.org/chromium/src/base/cancelable_callback.h?dr=CSs&l=91

[bokan, 2017/02/28 17:12:30]

Ok, that's fine, but I was still saying we should be ensuring we don't have both
fade in and out tasks posted at the same time.

+  delayed_scrollbar_fade_in_.Reset(base::Bind(
+      &ScrollbarAnimationController::FadeIn, weak_factory_.GetWeakPtr()));
+  client_->PostDelayedScrollbarAnimationTask(
+      delayed_scrollbar_fade_in_.callback(), fade_in_delay_);
+}
+
+void ScrollbarAnimationController::PostDelayedFadeOut(bool on_resize) {
+  base::TimeDelta delay = on_resize ? fade_out_resize_delay_ : fade_out_delay_;
+  delayed_scrollbar_fade_out_.Reset(
       base::Bind(&ScrollbarAnimationController::StartAnimation,
                  weak_factory_.GetWeakPtr()));
-  client_->PostDelayedScrollbarAnimationTask(delayed_scrollbar_fade_.callback(),
-                                             delay);
+  client_->PostDelayedScrollbarAnimationTask(
+      delayed_scrollbar_fade_out_.callback(), delay);
 }
 
 bool ScrollbarAnimationController::Animate(base::TimeTicks now) {
   bool animated = false;
 
   if (is_animating_) {
     if (last_awaken_time_.is_null())
       last_awaken_time_ = now;
 
     float progress = AnimationProgressAtTime(now);
     RunAnimationFrame(progress);
 
     if (is_animating_)
       client_->SetNeedsAnimateForScrollbarAnimation();
     animated = true;
   }
 
   if (need_thinning_animation_) {
     animated |= vertical_controller_->Animate(now);
     animated |= horizontal_controller_->Animate(now);
   }
 
   return animated;
 }
 
 float ScrollbarAnimationController::AnimationProgressAtTime(
     base::TimeTicks now) {
   base::TimeDelta delta = now - last_awaken_time_;
-  float progress = delta.InSecondsF() / fade_duration_.InSecondsF();
+  float progress = delta.InSecondsF() / fade_out_duration_.InSecondsF();
   return std::max(std::min(progress, 1.f), 0.f);
 }
 
 void ScrollbarAnimationController::DidScrollBegin() {
   currently_scrolling_ = true;
 }
 
 void ScrollbarAnimationController::RunAnimationFrame(float progress) {
   ApplyOpacityToScrollbars(1.f - progress);
   client_->SetNeedsRedrawForScrollbarAnimation();
   if (progress == 1.f)
     StopAnimation();
 }
 
 void ScrollbarAnimationController::DidScrollUpdate(bool on_resize) {
   if (need_thinning_animation_ && Captured())
     return;
 
   StopAnimation();
 
   // As an optimization, we avoid spamming fade delay tasks during active fast
   // scrolls.  But if we're not within one, we need to post every scroll update.
   if (!currently_scrolling_) {
     // We don't fade out scrollbar if they need thinning animation and mouse is
     // near.
     if (!need_thinning_animation_ || !mouse_is_near_any_scrollbar())
-      PostDelayedAnimationTask(on_resize);
+      PostDelayedFadeOut(on_resize);
   } else {
     scroll_gesture_has_scrolled_ = true;
   }
 
-  ApplyOpacityToScrollbars(1);
+  FadeIn();
 
   if (need_thinning_animation_) {
     vertical_controller_->UpdateThumbThicknessScale();
     horizontal_controller_->UpdateThumbThicknessScale();
   }
 }
 
 void ScrollbarAnimationController::DidScrollEnd() {
   bool has_scrolled = scroll_gesture_has_scrolled_;
   scroll_gesture_has_scrolled_ = false;
 
   currently_scrolling_ = false;
 
   // We don't fade out scrollbar if they need thinning animation and mouse is
   // near.
   if (need_thinning_animation_ && mouse_is_near_any_scrollbar())
     return;
 
   if (has_scrolled)
-    PostDelayedAnimationTask(false);
+    PostDelayedFadeOut(false);
 }
 
 void ScrollbarAnimationController::DidMouseDown() {
   if (!need_thinning_animation_ || ScrollbarsHidden())
     return;
 
   vertical_controller_->DidMouseDown();
   horizontal_controller_->DidMouseDown();
 }
 
 void ScrollbarAnimationController::DidMouseUp() {
   if (!need_thinning_animation_)
     return;
 
   vertical_controller_->DidMouseUp();
   horizontal_controller_->DidMouseUp();
 
   if (!mouse_is_near_any_scrollbar())
-    PostDelayedAnimationTask(false);
+    PostDelayedFadeOut(false);
 }
 
 void ScrollbarAnimationController::DidMouseLeave() {
   if (!need_thinning_animation_)
     return;
 
   vertical_controller_->DidMouseLeave();
   horizontal_controller_->DidMouseLeave();
 
   if (ScrollbarsHidden() || Captured())
     return;
 
-  PostDelayedAnimationTask(false);
+  PostDelayedFadeOut(false);
 }
 
 void ScrollbarAnimationController::DidMouseMoveNear(
     ScrollbarOrientation orientation,
     float distance) {
   if (!need_thinning_animation_)
     return;
 
+  bool need_trigger_scrollbar_fade_in_before = need_trigger_scrollbar_fade_in_;
+
   GetScrollbarAnimationController(orientation).DidMouseMoveNear(distance);
 
-  if (ScrollbarsHidden() || Captured())
+  need_trigger_scrollbar_fade_in_ =
+      CalcNeedTriggerScrollbarFadeIn(orientation, distance);
+
+  if (Captured())
     return;
 
-  if (mouse_is_near_any_scrollbar()) {
-    ApplyOpacityToScrollbars(1);
-    StopAnimation();
-  } else if (!is_animating_) {
-    PostDelayedAnimationTask(false);
+  if (ScrollbarsHidden()) {
+    if (need_trigger_scrollbar_fade_in_before !=
+        need_trigger_scrollbar_fade_in_) {
+      if (need_trigger_scrollbar_fade_in_) {
+        PostDelayedFadeIn();
+      } else {
+        delayed_scrollbar_fade_in_.Cancel();
+      }
+    }
+  } else {
+    if (mouse_is_near_any_scrollbar()) {
+      FadeIn();
+      StopAnimation();
+    } else if (!is_animating_) {
+      PostDelayedFadeOut(false);
+    }
   }
 }
 
+bool ScrollbarAnimationController::CalcNeedTriggerScrollbarFadeIn(
+    ScrollbarOrientation orientation,
+    float distance) const {
+  DCHECK(need_thinning_animation_);
+
+  if (vertical_controller_->mouse_is_over_scrollbar() ||
+      horizontal_controller_->mouse_is_over_scrollbar())
+    return true;
+
+  for (ScrollbarLayerImplBase* scrollbar : Scrollbars()) {
+    if (scrollbar->orientation() != orientation)
+      continue;
+
+    if (scrollbar->ThumbThickness() + distance <

[bokan, 2017/02/28 14:04:49]

Nit: I think this would be clearer as |distance < kMouseMoveDistance -
ThumbThickness|

+        kMouseMoveDistanceToTriggerFadeInAnimation)
+      return true;
+  }
+
+  return false;
+}
+
 bool ScrollbarAnimationController::mouse_is_over_scrollbar(
     ScrollbarOrientation orientation) const {
   DCHECK(need_thinning_animation_);
   return GetScrollbarAnimationController(orientation).mouse_is_over_scrollbar();
 }
 
 bool ScrollbarAnimationController::mouse_is_near_scrollbar(
     ScrollbarOrientation orientation) const {
   DCHECK(need_thinning_animation_);
   return GetScrollbarAnimationController(orientation).mouse_is_near_scrollbar();
 }
 
 bool ScrollbarAnimationController::mouse_is_near_any_scrollbar() const {
   DCHECK(need_thinning_animation_);
   return vertical_controller_->mouse_is_near_scrollbar() ||
          horizontal_controller_->mouse_is_near_scrollbar();
 }
 
 bool ScrollbarAnimationController::ScrollbarsHidden() const {
   return opacity_ == 0.0f;
 }
 
 bool ScrollbarAnimationController::Captured() const {
   DCHECK(need_thinning_animation_);
   return vertical_controller_->captured() || horizontal_controller_->captured();
 }
 
+void ScrollbarAnimationController::FadeIn() {
+  ApplyOpacityToScrollbars(1.0f);
+}
+
 void ScrollbarAnimationController::ApplyOpacityToScrollbars(float opacity) {
   for (ScrollbarLayerImplBase* scrollbar : Scrollbars()) {
     if (!scrollbar->is_overlay_scrollbar())
       continue;
     float effective_opacity = scrollbar->CanScrollOrientation() ? opacity : 0;
     PropertyTrees* property_trees =
         scrollbar->layer_tree_impl()->property_trees();
     // If this method is called during LayerImpl::PushPropertiesTo, we may not
     // yet have valid layer_id_to_effect_node_index entries as property trees
     // are pushed after layers during activation. We can skip updating opacity
@@ skipping 11 matching lines @@
   bool previouslyVisible = opacity_ > 0.0f;
   bool currentlyVisible = opacity > 0.0f;
 
   opacity_ = opacity;
 
   if (previouslyVisible != currentlyVisible)
     client_->DidChangeScrollbarVisibility();
 }
 
 }  // namespace cc