Prevent overlay scrollbars expand or hover together

cc/input/single_scrollbar_animation_controller_thinning.cc

Index: cc/input/single_scrollbar_animation_controller_thinning.cc
diff --git a/cc/input/single_scrollbar_animation_controller_thinning.cc b/cc/input/single_scrollbar_animation_controller_thinning.cc
new file mode 100644
index 0000000000000000000000000000000000000000..d2ba28b197fdec3b5567292453321518f1efbb84
--- /dev/null
+++ b/cc/input/single_scrollbar_animation_controller_thinning.cc
@@ -0,0 +1,204 @@
+// Copyright 2013 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/single_scrollbar_animation_controller_thinning.h"
+
+#include <algorithm>
+
+#include "base/memory/ptr_util.h"
+#include "base/time/time.h"
+#include "cc/input/scrollbar_animation_controller.h"
+#include "cc/layers/layer_impl.h"
+#include "cc/layers/scrollbar_layer_impl_base.h"
+#include "cc/trees/layer_tree_impl.h"
+
+namespace {
+const float kIdleThicknessScale = 0.4f;
+const float kDefaultMouseMoveDistanceToTriggerAnimation = 25.f;
+}
+
+namespace cc {
+
+std::unique_ptr<SingleScrollbarAnimationControllerThinning>
+SingleScrollbarAnimationControllerThinning::Create(
+    int scroll_layer_id,
+    ScrollbarOrientation orientation,
+    ScrollbarAnimationControllerClient* client,
+    base::TimeDelta thinning_duration) {
+  return base::WrapUnique(new SingleScrollbarAnimationControllerThinning(
+      scroll_layer_id, orientation, client, thinning_duration));
+}
+
+SingleScrollbarAnimationControllerThinning::
+    SingleScrollbarAnimationControllerThinning(
+        int scroll_layer_id,
+        ScrollbarOrientation orientation,
+        ScrollbarAnimationControllerClient* client,
+        base::TimeDelta thinning_duration)
+    : client_(client),
+      is_animating_(false),
+      scroll_layer_id_(scroll_layer_id),
+      orientation_(orientation),
+      captured_(false),
+      mouse_is_over_scrollbar_(false),
+      mouse_is_near_scrollbar_(false),
+      thickness_change_(NONE),
+      mouse_move_distance_to_trigger_animation_(
+          kDefaultMouseMoveDistanceToTriggerAnimation),
+      thinning_duration_(thinning_duration) {
+  ApplyThumbThicknessScale(kIdleThicknessScale);
+}
+
+bool SingleScrollbarAnimationControllerThinning::Animate(base::TimeTicks now) {
+  if (!is_animating_)
+    return false;
+
+  if (last_awaken_time_.is_null())
+    last_awaken_time_ = now;
+
+  float progress = AnimationProgressAtTime(now);
+  RunAnimationFrame(progress);
+
+  return true;
+}
+
+float SingleScrollbarAnimationControllerThinning::AnimationProgressAtTime(
+    base::TimeTicks now) {
+  base::TimeDelta delta = now - last_awaken_time_;
+  float progress = delta.InSecondsF() / Duration().InSecondsF();
+  return std::max(std::min(progress, 1.f), 0.f);
+}
+
+const base::TimeDelta& SingleScrollbarAnimationControllerThinning::Duration() {
+  return thinning_duration_;
+}
+
+void SingleScrollbarAnimationControllerThinning::RunAnimationFrame(
+    float progress) {
+  if (captured_)
+    return;
+
+  ApplyThumbThicknessScale(ThumbThicknessScaleAt(progress));
+
+  client_->SetNeedsRedrawForScrollbarAnimation();
+  if (progress == 1.f) {
+    StopAnimation();
+    thickness_change_ = NONE;
+  }
+}
+
+void SingleScrollbarAnimationControllerThinning::StartAnimation() {
+  is_animating_ = true;
+  last_awaken_time_ = base::TimeTicks();
+  client_->SetNeedsAnimateForScrollbarAnimation();
+}
+
+void SingleScrollbarAnimationControllerThinning::StopAnimation() {
+  is_animating_ = false;
+}
+
+void SingleScrollbarAnimationControllerThinning::DidMouseDown() {
+  if (!mouse_is_over_scrollbar_)
+    return;
+
+  StopAnimation();
+  captured_ = true;
+  ApplyThumbThicknessScale(1.f);
+}
+
+void SingleScrollbarAnimationControllerThinning::DidMouseUp() {
+  if (!captured_)
+    return;
+
+  captured_ = false;
+  StopAnimation();
+
+  if (!mouse_is_near_scrollbar_) {
+    thickness_change_ = DECREASE;
+    StartAnimation();
+  } else {
+    thickness_change_ = NONE;
+  }
+}
+
+void SingleScrollbarAnimationControllerThinning::DidMouseLeave() {
+  if (!mouse_is_over_scrollbar_ && !mouse_is_near_scrollbar_)
+    return;
+
+  mouse_is_over_scrollbar_ = false;
+  mouse_is_near_scrollbar_ = false;
+
+  if (captured_)
+    return;
+
+  thickness_change_ = DECREASE;
+  StartAnimation();
+}
+
+void SingleScrollbarAnimationControllerThinning::DidMouseMoveNear(
+    float distance) {
+  bool mouse_is_over_scrollbar = distance == 0.0f;
+  bool mouse_is_near_scrollbar =
+      distance < mouse_move_distance_to_trigger_animation_;
+
+  if (!captured_ && mouse_is_near_scrollbar != mouse_is_near_scrollbar_) {
+    thickness_change_ = mouse_is_near_scrollbar ? INCREASE : DECREASE;
+    StartAnimation();
+  }
+  mouse_is_near_scrollbar_ = mouse_is_near_scrollbar;
+  mouse_is_over_scrollbar_ = mouse_is_over_scrollbar;
+}
+
+float SingleScrollbarAnimationControllerThinning::ThumbThicknessScaleAt(
+    float progress) {
+  if (thickness_change_ == NONE)
+    return mouse_is_near_scrollbar_ ? 1.f : kIdleThicknessScale;
+  float factor = thickness_change_ == INCREASE ? progress : (1.f - progress);
+  return ((1.f - kIdleThicknessScale) * factor) + kIdleThicknessScale;
+}
+
+float SingleScrollbarAnimationControllerThinning::AdjustScale(
+    float new_value,
+    float current_value,
+    AnimationChange animation_change,
+    float min_value,
+    float max_value) {
+  float result;
+  if (animation_change == INCREASE && current_value > new_value)
+    result = current_value;
+  else if (animation_change == DECREASE && current_value < new_value)
+    result = current_value;
+  else
+    result = new_value;
+  if (result > max_value)
+    return max_value;
+  if (result < min_value)
+    return min_value;
+  return result;
+}
+
+void SingleScrollbarAnimationControllerThinning::UpdateThumbThicknessScale() {
+  StopAnimation();
+  ApplyThumbThicknessScale(mouse_is_near_scrollbar_ ? 1.f
+                                                    : kIdleThicknessScale);
+}
+
+void SingleScrollbarAnimationControllerThinning::ApplyThumbThicknessScale(
+    float thumb_thickness_scale) {
+  for (ScrollbarLayerImplBase* scrollbar :
+       client_->ScrollbarsFor(scroll_layer_id_)) {
+    if (scrollbar->orientation() != orientation_)
+      continue;
+    if (!scrollbar->is_overlay_scrollbar())
+      continue;
+
+    float scale = AdjustScale(thumb_thickness_scale,
+                              scrollbar->thumb_thickness_scale_factor(),
+                              thickness_change_, kIdleThicknessScale, 1);
+
+    scrollbar->SetThumbThicknessScaleFactor(scale);
+  }
+}
+
+}  // namespace cc