Adding ripple effect for clicks on MD slider

ui/views/controls/md_slider.cc

 // Copyright 2016 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/controls/md_slider.h"
 
 #include "third_party/skia/include/core/SkColor.h"
 #include "third_party/skia/include/core/SkPaint.h"
+#include "ui/gfx/animation/slide_animation.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/views/controls/slider.h"
 
 namespace views {
 
 // Color of slider at the active and the disabled state, respectively.
 const SkColor kActiveColor = SkColorSetARGB(0xFF, 0x42, 0x85, 0xF4);
 const SkColor kDisabledColor = SkColorSetARGB(0x42, 0x00, 0x00, 0x00);
+const uint8_t kHighlightColorAlpha = 0x4D;
 
 // The thickness of the slider.
 const int kLineThickness = 2;
 
-// The radius of the thumb of the slider.
-const int kThumbRadius = 6;
+// The radius of the thumb and the highlighted thumb of the slider,
+// respectively.
+const float kThumbRadius = 6.f;
+const float kThumbHighlightRadius = 10.f;
 
 // The stroke of the thumb when the slider is disabled.
 const int kThumbStroke = 2;
 
+// Duration of the thumb highlight growing effect animation.
+const int kSlideHighlightChangeDurationMs = 150;
+
 MdSlider::MdSlider(SliderListener* listener)
-    : Slider(listener), is_active_(true) {
+    : Slider(listener), is_active_(true), thumb_highlight_radius_(0.f) {
   SchedulePaint();
 }
 
 MdSlider::~MdSlider() {}
 
 void MdSlider::OnPaint(gfx::Canvas* canvas) {
   Slider::OnPaint(canvas);
 
   // Paint the slider.
-  const int thumb_size = kThumbRadius * 2;
   const gfx::Rect content = GetContentsBounds();
-  const int width = content.width() - thumb_size;
+  const int width = content.width() - kThumbRadius * 2;
   const int full = GetAnimatingValue() * width;
   const int empty = width - full;
   const int y = content.height() / 2 - kLineThickness / 2;
+  const int x = content.x() + full + kThumbRadius;
+  const SkColor current_thumb_color =
+      is_active_ ? kActiveColor : kDisabledColor;
   canvas->FillRect(gfx::Rect(content.x(), y, full, kLineThickness),
-                   is_active_ ? kActiveColor : kDisabledColor);
-  canvas->FillRect(
-      gfx::Rect(content.x() + full + thumb_size, y, empty, kLineThickness),
-      kDisabledColor);
+                   current_thumb_color);
+  canvas->FillRect(gfx::Rect(x + kThumbRadius, y, empty, kLineThickness),
+                   kDisabledColor);
+
+  gfx::Point thumb_center(x, content.height() / 2);
+
+  // Paint the thumb highlight if it exists.
+  if (is_active_ && thumb_highlight_radius_ > kThumbRadius) {
+    SkPaint highlight;
+    SkColor kHighlightColor = SkColorSetA(kActiveColor, kHighlightColorAlpha);
+    highlight.setColor(kHighlightColor);
+    highlight.setFlags(SkPaint::kAntiAlias_Flag);
+    canvas->DrawCircle(thumb_center, thumb_highlight_radius_, highlight);
+  }
 
   // Paint the thumb of the slider.
   SkPaint paint;
-  paint.setColor(is_active_ ? kActiveColor : kDisabledColor);
+  paint.setColor(current_thumb_color);
   paint.setFlags(SkPaint::kAntiAlias_Flag);
 
   if (!is_active_) {
     paint.setStrokeWidth(kThumbStroke);
     paint.setStyle(SkPaint::kStroke_Style);
   }
   canvas->DrawCircle(
-      gfx::Point(content.x() + full + kThumbRadius, content.height() / 2),
+      thumb_center,
       is_active_ ? kThumbRadius : (kThumbRadius - kThumbStroke / 2), paint);
 }
 
 const char* MdSlider::GetClassName() const {
   return "MdSlider";
 }
 
 void MdSlider::UpdateState(bool control_on) {
   is_active_ = control_on;
   SchedulePaint();
 }
 
 int MdSlider::GetThumbWidth() {
   return kThumbRadius * 2;
 }
+
+void MdSlider::SetHighlighted(bool is_highlighted) {
+  if (!highlight_animation_) {
+    if (!is_highlighted)
+      return;
+
+    highlight_animation_.reset(new gfx::SlideAnimation(this));
+    highlight_animation_->SetSlideDuration(kSlideHighlightChangeDurationMs);
+  }
+  if (is_highlighted)
+    highlight_animation_->Show();
+  else
+    highlight_animation_->Hide();
+}
+
+void MdSlider::AnimationProgressed(const gfx::Animation* animation) {
+  if (animation != highlight_animation_.get()) {
+    Slider::AnimationProgressed(animation);
+    return;
+  }
+  thumb_highlight_radius_ =
+      animation->CurrentValueBetween(kThumbRadius, kThumbHighlightRadius);
+  SchedulePaint();
+}
+
+void MdSlider::AnimationEnded(const gfx::Animation* animation) {
+  if (animation != highlight_animation_.get()) {
+    Slider::AnimationEnded(animation);
+    return;
+  }
+  if (animation == highlight_animation_.get() &&
+      !highlight_animation_->IsShowing()) {
+    highlight_animation_.reset();
+  }
+}
+
 }  // namespace views