MacViews: Overlay Scrollbars with Show/Hide Animations

ui/views/controls/scrollbar/cocoa_scroll_bar.h

+// 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.
+
+#ifndef UI_VIEWS_CONTROLS_SCROLLBAR_COCOA_SCROLL_BAR_H_
+#define UI_VIEWS_CONTROLS_SCROLLBAR_COCOA_SCROLL_BAR_H_
+
+#include "base/macros.h"
+#import "base/mac/scoped_nsobject.h"
+#import "ui/views/cocoa/views_scrollbar_bridge.h"
+#include "ui/views/controls/scrollbar/base_scroll_bar.h"
+#include "ui/views/views_export.h"
+
+namespace views {
+
+// The transparent scrollbar for Mac which overlays its contents.
+class VIEWS_EXPORT CocoaScrollBar : public BaseScrollBar,
+                                    public ViewsScrollbarBridgeDelegate {
+ public:
+  explicit CocoaScrollBar(bool horizontal);
+  ~CocoaScrollBar() override;
+
+  // Called by CocoaScrollBarThumb when the mouse enters or exits the view.
+  void OnMouseEnteredScrollbarThumb(const ui::MouseEvent& event);
+  void OnMouseExitedScrollbarThumb(const ui::MouseEvent& event);
+
+  // ScrollDelegate:
+  bool OnScroll(float dx, float dy) override;
+
+  // ViewsScrollbarBridgeDelegate:
+  void OnScrollerStyleChanged() override;
+
+ protected:
+  // BaseScrollBar:
+  gfx::Rect GetTrackBounds() const override;
+
+  // ScrollBar:
+  int GetLayoutSize() const override;
+  int GetContentOverlapSize() const override;
+
+  // View:
+  gfx::Size GetPreferredSize() const override;
+  void OnPaint(gfx::Canvas* canvas) override;
+
+ private:
+  // Methods to change the visibility of the scrollbar.
+  void ShowScrollbar();
+  void HideScrollbar();
+
+  // Resets hide_scrollbar_timer_ if the timer is running. Otherwise, this
+  // method will just start the timer.
+  void ResetTimer();
+
+  // Scroller style the scrollbar is using.
+  NSScrollerStyle scroller_style_;
+
+  // Timer that will start the scrollbar's hiding animation when it reaches 0.
+  base::OneShotTimer hide_scrollbar_timer_;

[tapted, 2016/02/17 08:46:20]

I think it might be nicer just to use a base::Timer directly, and initialize it
in the constructor with all the arguments to Start(..)

Then we don't need ResetTimer() -- simply calling hide_scrollbar_timer_.Reset()
seems to be enough. But I might not have groked the timer documentation entirely
correctly.

[spqchan, 2016/02/19 00:14:02]

Done

+
+  // True when the scrolltrack should be drawn.
+  bool has_scrolltrack_;
+
+  // True if the scrollbar is in its hover state.
+  bool is_hovering_;
+
+  // The bridge for NSScroller.
+  base::scoped_nsobject<ViewsScrollbarBridge> bridge_;
+
+  DISALLOW_COPY_AND_ASSIGN(CocoaScrollBar);
+};
+
+}  // namespace views
+
+#endif  // UI_VIEWS_CONTROLS_SCROLLBAR_COCOA_SCROLL_BAR_H_