Added material design mouse hover feedback support.

ui/views/animation/ink_drop_hover.cc

+// Copyright 2015 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 "ui/views/animation/ink_drop_hover.h"
+
+#include "third_party/skia/include/core/SkColor.h"
+#include "ui/compositor/callback_layer_animation_observer.h"
+#include "ui/compositor/layer.h"
+#include "ui/compositor/layer_animation_sequence.h"
+#include "ui/compositor/scoped_layer_animation_settings.h"
+#include "ui/views/animation/ink_drop_painted_layer_delegates.h"
+
+namespace views {
+
+namespace {
+
+// The opacity of the hover when it is visible.
+const float kHoverVisibleOpacity = 0.08f;
+
+// The opacity of the hover when it is not visible.
+const float kHiddenOpacity = 0.0f;
+
+// The hover color.
+const SkColor kHoverColor = SK_ColorBLACK;
+
+}  // namespace
+
+InkDropHover::InkDropHover(const gfx::Size& size, int corner_radius)
+    : layer_delegate_(
+          new RoundedRectangleLayerDelegate(kHoverColor, size, corner_radius)),
+      layer_(new ui::Layer()) {
+  layer_->SetBounds(gfx::Rect(size));
+  layer_->SetFillsBoundsOpaquely(false);
+  layer_->set_delegate(layer_delegate_.get());
+  layer_->SetVisible(false);
+  layer_->SetOpacity(kHoverVisibleOpacity);
+  layer_->SetMasksToBounds(false);
+  layer_->set_name("InkDropHover:layer");
+  SetCenterPoint(gfx::Rect(size).CenterPoint());
+}
+
+InkDropHover::~InkDropHover() {}
+
+bool InkDropHover::IsVisible() const {
+  return layer_->visible();
+}
+
+void InkDropHover::FadeIn(const base::TimeDelta& duration) {
+  layer_->SetOpacity(kHiddenOpacity);
+  layer_->SetVisible(true);
+  AnimateFade(FADE_IN, duration);
+}
+
+void InkDropHover::FadeOut(const base::TimeDelta& duration) {
+  AnimateFade(FADE_OUT, duration);
+}
+
+void InkDropHover::AnimateFade(HoverAnimationType animation_type,
+                               const base::TimeDelta& duration) {
+  // The |animation_observer| will be destroyed when the
+  // AnimationStartedCallback() returns true.
+  ui::CallbackLayerAnimationObserver* animation_observer =
+      new ui::CallbackLayerAnimationObserver(
+          base::Bind(&InkDropHover::AnimationEndedCallback,
+                     base::Unretained(this), animation_type));
+
+  ui::LayerAnimator* animator = layer_->GetAnimator();
+  ui::ScopedLayerAnimationSettings animation(animator);
+  animation.SetPreemptionStrategy(
+      ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
+  ui::LayerAnimationElement* animation_element =
+      ui::LayerAnimationElement::CreateOpacityElement(
+          animation_type == FADE_IN ? kHoverVisibleOpacity : kHiddenOpacity,
+          duration);
+  ui::LayerAnimationSequence* animation_sequence =
+      new ui::LayerAnimationSequence(animation_element);
+  animation_sequence->AddObserver(animation_observer);
+
+  animator->StartAnimation(animation_sequence);
+
+  animation_observer->SetActive();
+}
+
+void InkDropHover::SetCenterPoint(const gfx::Point& center_point) {
+  gfx::Transform transform;
+  transform.Translate(center_point.x() - layer_->bounds().CenterPoint().x(),
+                      center_point.y() - layer_->bounds().CenterPoint().y());
+  layer_->SetTransform(transform);
+}
+
+bool InkDropHover::AnimationEndedCallback(
+    HoverAnimationType animation_type,
+    const ui::CallbackLayerAnimationObserver& observer) {
+  switch (animation_type) {
+    case FADE_IN:
+      break;
+    case FADE_OUT:

[varkha, 2016/01/22 15:45:32]

Not sure if this could be an if(FADE_OUT).

[bruthig, 2016/01/25 22:39:17]

Done.

+      layer_->SetVisible(false);
+      break;
+  }
+  return true;
+}
+
+}  // namespace views