MacViews: Overlay Scrollbars with Show/Hide Animations

ui/views/controls/scrollbar/cocoa_scroll_bar.mm

+// 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.
+
+#import "ui/views/controls/scrollbar/cocoa_scroll_bar.h"
+
+#import "base/mac/sdk_forward_declarations.h"
+#include "third_party/skia/include/core/SkColor.h"
+#include "third_party/skia/include/effects/SkGradientShader.h"
+#include "ui/compositor/layer.h"
+#include "ui/compositor/layer_animator.h"
+#include "ui/compositor/scoped_layer_animation_settings.h"
+#include "ui/gfx/canvas.h"
+#include "ui/views/controls/scrollbar/base_scroll_bar_thumb.h"
+
+namespace views {
+
+namespace {
+
+// The length of the fade animation.
+const int kFadeDurationMs = 240;
+
+// How long we should wait before hiding the scrollbar.
+const int kScrollbarHideTimeoutMs = 500;
+
+// The width of the scrollbar.
+const int kScrollbarWidth = 15;
+
+// The width of the scrollbar thumb.
+const int kScrollbarThumbWidth = 10;
+
+// The width of the scroller track border.
+const int kScrollerTrackBorderWidth = 1;
+
+// The amount the thumb is inset from both the ends and the sides of the track.
+const int kScrollbarThumbInset = 3;
+
+// Scrollbar thumb colors.
+const SkColor kScrollerDefaultThumbColor = SkColorSetARGB(0x38, 0, 0, 0);
+const SkColor kScrollerHoverThumbColor = SkColorSetARGB(0x80, 0, 0, 0);
+
+// Scroller track colors.
+// TODO(spqchan): Add an alpha channel for the overlay-style scroll track.
+const SkColor kScrollerTrackGradientColors[] = {
+    SkColorSetRGB(0xEF, 0xEF, 0xEF), SkColorSetRGB(0xF9, 0xF9, 0xF9),
+    SkColorSetRGB(0xFD, 0xFD, 0xFD), SkColorSetRGB(0xF6, 0xF6, 0xF6)};
+const SkColor kScrollerTrackInnerBorderColor = SkColorSetRGB(0xE4, 0xE4, 0xE4);
+const SkColor kScrollerTrackOuterBorderColor = SkColorSetRGB(0xEF, 0xEF, 0xEF);
+
+//////////////////////////////////////////////////////////////////
+// CocoaScrollBarThumb
+
+class CocoaScrollBarThumb : public BaseScrollBarThumb {
+ public:
+  explicit CocoaScrollBarThumb(CocoaScrollBar* scroll_bar);
+  ~CocoaScrollBarThumb() override;
+
+  // Returns true if the thumb is in hover or pressed state.
+  bool IsStateHoverOrPressed();
+
+ protected:
+  // View:
+  gfx::Size GetPreferredSize() const override;
+  void OnPaint(gfx::Canvas* canvas) override;
+  void OnMouseEntered(const ui::MouseEvent& event) override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(CocoaScrollBarThumb);
+};
+
+CocoaScrollBarThumb::CocoaScrollBarThumb(CocoaScrollBar* scroll_bar)
+    : BaseScrollBarThumb(scroll_bar) {
+  DCHECK(scroll_bar);
+
+  // This is necessary, otherwise the thumb will be rendered below the views if
+  // those views paint to their own layers.
+  SetPaintToLayer(true);
+  SetFillsBoundsOpaquely(false);
+}
+
+CocoaScrollBarThumb::~CocoaScrollBarThumb() {}
+
+bool CocoaScrollBarThumb::IsStateHoverOrPressed() {
+  CustomButton::ButtonState state = GetState();
+  return state == CustomButton::STATE_HOVERED ||
+         state == CustomButton::STATE_PRESSED;
+}
+
+gfx::Size CocoaScrollBarThumb::GetPreferredSize() const {
+  return gfx::Size(kScrollbarThumbWidth, kScrollbarThumbWidth);
+}
+
+void CocoaScrollBarThumb::OnPaint(gfx::Canvas* canvas) {
+  CocoaScrollBar* scrollbar = static_cast<CocoaScrollBar*>(scroll_bar());
+  DCHECK(scrollbar);
+
+  SkColor thumb_color = kScrollerDefaultThumbColor;
+  if (scrollbar->GetScrollerStyle() == NSScrollerStyleOverlay ||
+      IsStateHoverOrPressed()) {
+    thumb_color = kScrollerHoverThumbColor;
+  }
+
+  gfx::Rect local_bounds(GetLocalBounds());
+  SkPaint paint;
+  paint.setAntiAlias(true);
+  paint.setStyle(SkPaint::kFill_Style);
+  paint.setColor(thumb_color);
+  const SkScalar radius = std::min(local_bounds.width(), local_bounds.height());
+  canvas->DrawRoundRect(local_bounds, radius, paint);
+}
+
+void CocoaScrollBarThumb::OnMouseEntered(const ui::MouseEvent& event) {
+  BaseScrollBarThumb::OnMouseEntered(event);
+  CocoaScrollBar* scrollbar = static_cast<CocoaScrollBar*>(scroll_bar());
+  scrollbar->OnMouseEnteredScrollbarThumb(event);
+}
+
+}  // namespace
+
+//////////////////////////////////////////////////////////////////
+// CocoaScrollBar class
+
+CocoaScrollBar::CocoaScrollBar(bool horizontal)
+    : BaseScrollBar(horizontal, new CocoaScrollBarThumb(this)),
+      hide_scrollbar_timer_(
+          FROM_HERE,
+          base::TimeDelta::FromMilliseconds(kScrollbarHideTimeoutMs),
+          base::Bind(&CocoaScrollBar::HideScrollbar, base::Unretained(this)),
+          false) {
+  bridge_.reset([[ViewsScrollbarBridge alloc] initWithDelegate:this]);
+
+  scroller_style_ = [ViewsScrollbarBridge getPreferredScrollerStyle];
+
+  SetPaintToLayer(true);
+  has_scrolltrack_ = scroller_style_ == NSScrollerStyleLegacy;
+  layer()->SetOpacity(scroller_style_ == NSScrollerStyleOverlay ? 0.0 : 1.0);
+}
+
+CocoaScrollBar::~CocoaScrollBar() {
+  [bridge_ clearDelegate];
+}
+
+//////////////////////////////////////////////////////////////////
+// CocoaScrollBar, BaseScrollBar:
+
+gfx::Rect CocoaScrollBar::GetTrackBounds() const {
+  gfx::Rect local_bounds(GetLocalBounds());
+  local_bounds.Inset(kScrollbarThumbInset, kScrollbarThumbInset);
+
+  gfx::Size track_size = local_bounds.size();
+  track_size.SetToMax(GetThumb()->size());
+  local_bounds.set_size(track_size);
+  return local_bounds;
+}
+
+//////////////////////////////////////////////////////////////////
+// CocoaScrollBar, ScrollBar:
+
+int CocoaScrollBar::GetLayoutSize() const {
+  return scroller_style_ == NSScrollerStyleOverlay ? 0 : kScrollbarWidth;
+}
+
+int CocoaScrollBar::GetContentOverlapSize() const {
+  return scroller_style_ == NSScrollerStyleLegacy ? 0 : kScrollbarWidth;
+}
+
+//////////////////////////////////////////////////////////////////
+// CocoaScrollBar::Views:
+
+void CocoaScrollBar::Layout() {
+  GetThumb()->SetBoundsRect(GetTrackBounds());
+}
+
+gfx::Size CocoaScrollBar::GetPreferredSize() const {
+  return gfx::Size();
+}
+
+void CocoaScrollBar::OnPaint(gfx::Canvas* canvas) {
+  if (!has_scrolltrack_)
+    return;
+
+  // Paint the scrollbar track background.
+  gfx::Rect track_rect = GetLocalBounds();
+
+  SkPoint gradient_bounds[2];
+  if (IsHorizontal()) {
+    gradient_bounds[0].set(track_rect.x(), track_rect.y());
+    gradient_bounds[1].set(track_rect.x(), track_rect.bottom());
+  } else {
+    gradient_bounds[0].set(track_rect.x(), track_rect.y());
+    gradient_bounds[1].set(track_rect.right(), track_rect.y());
+  }
+  skia::RefPtr<SkShader> shader = skia::AdoptRef(SkGradientShader::CreateLinear(
+      gradient_bounds, kScrollerTrackGradientColors, nullptr,
+      arraysize(kScrollerTrackGradientColors), SkShader::kClamp_TileMode));
+  SkPaint gradient;
+  gradient.setShader(shader.get());
+  canvas->DrawRect(track_rect, gradient);
+
+  // Draw the inner border: top if horizontal, left if vertical.
+  SkPaint paint;
+  paint.setColor(kScrollerTrackInnerBorderColor);
+  gfx::Rect inner_border(track_rect);
+  if (IsHorizontal())
+    inner_border.set_height(kScrollerTrackBorderWidth);
+  else
+    inner_border.set_width(kScrollerTrackBorderWidth);
+  canvas->DrawRect(inner_border, paint);
+
+  // Draw the outer border: bottom if horizontal, right if veritcal.
+  paint.setColor(kScrollerTrackOuterBorderColor);
+  gfx::Rect outer_border(inner_border);
+  if (IsHorizontal())
+    outer_border.set_y(track_rect.bottom());
+  else
+    outer_border.set_x(track_rect.right());
+  canvas->DrawRect(outer_border, paint);
+}
+
+void CocoaScrollBar::OnMouseEnteredScrollbarThumb(const ui::MouseEvent& event) {
+  if (scroller_style_ != NSScrollerStyleOverlay)
+    return;
+
+  // If the scrollbar thumb has not compeletely faded away, then reshow it when
+  // the mouse enters the scrollbar thumb.
+  if (layer()->opacity())
+    ShowScrollbar();
+
+  hide_scrollbar_timer_.Reset();
+}
+
+//////////////////////////////////////////////////////////////////
+// CocoaScrollBar::ScrollDelegate:
+
+bool CocoaScrollBar::OnScroll(float dx, float dy) {
+  bool did_scroll = BaseScrollBar::OnScroll(dx, dy);
+  if (did_scroll && scroller_style_ == NSScrollerStyleOverlay) {
+    ShowScrollbar();
+    hide_scrollbar_timer_.Reset();
+  }
+  return did_scroll;
+}
+
+//////////////////////////////////////////////////////////////////
+// CocoaScrollBar::ViewsScrollbarBridge:
+
+void CocoaScrollBar::OnScrollerStyleChanged() {
+  NSScrollerStyle scroller_style =
+      [ViewsScrollbarBridge getPreferredScrollerStyle];
+  if (scroller_style_ == scroller_style)
+    return;
+
+  scroller_style_ = scroller_style;
+
+  // Ensure that the ScrollView updates the scrollbar's layout.
+  if (parent())
+    parent()->Layout();
+
+  if (scroller_style_ == NSScrollerStyleOverlay)
+    // Hide the scrollbar, but don't fade out.

[tapted, 2016/02/22 23:41:56]

nit: comments count towards the needs-curlies rule, so the `if` and the `else`
should get curlies (I like the clearer comment :)).

[spqchan, 2016/02/23 17:56:27]

Done.

+    layer()->SetOpacity(0.0);
+  else
+    ShowScrollbar();
+}
+
+//////////////////////////////////////////////////////////////////
+// CocoaScrollBar, private:
+
+void CocoaScrollBar::HideScrollbar() {
+  DCHECK_EQ(scroller_style_, NSScrollerStyleOverlay);
+
+  // If the thumb is in a hover or pressed state, we don't want the scrollbar
+  // to disappear. As such, we should reset the timer.
+  CocoaScrollBarThumb* thumb = static_cast<CocoaScrollBarThumb*>(GetThumb());
+  if (thumb->IsStateHoverOrPressed()) {
+    hide_scrollbar_timer_.Reset();
+    return;
+  }
+
+  ui::ScopedLayerAnimationSettings animation(layer()->GetAnimator());
+  animation.SetTransitionDuration(
+      base::TimeDelta::FromMilliseconds(kFadeDurationMs));
+  layer()->SetOpacity(0.0);
+}
+
+void CocoaScrollBar::ShowScrollbar() {
+  // Updates the scrolltrack and repaint it, if necessary.
+  CocoaScrollBarThumb* thumb = static_cast<CocoaScrollBarThumb*>(GetThumb());
+  bool has_scrolltrack = scroller_style_ == NSScrollerStyleLegacy ||
+                         thumb->IsStateHoverOrPressed();
+  if (has_scrolltrack_ != has_scrolltrack) {
+    has_scrolltrack_ = has_scrolltrack;
+    SchedulePaint();
+  }
+
+  layer()->SetOpacity(1.0);
+  hide_scrollbar_timer_.Stop();
+}
+
+}  // namespace views