MacViews: Overlay Scrollbars with Show/Hide Animations

ui/views/controls/scrollbar/native_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.
+
+#include "ui/views/controls/scrollbar/native_cocoa_scroll_bar.h"
+
+#include "ui/gfx/animation/tween.h"
+#include "ui/views/controls/button/custom_button.h"
+#include "ui/views/controls/scrollbar/native_scroll_bar_wrapper.h"
+
+namespace views {
+
+namespace {
+// How long we should wait before hiding the scrollbar.

[tapted, 2016/02/08 00:31:15]

nit: blank line before

[spqchan, 2016/02/09 21:21:26]

Done.

+const int kScrollbarHideTimeoutMs = 300;
+
+// How many frames per second to target.
+const int kFadeFrameRateHz = 60;
+
+// How long animations should take by default.
+const int kFadeDurationMs = 120;
+}

[tapted, 2016/02/08 00:31:15]

nit: }  // namespace

(also, blank line before)

[spqchan, 2016/02/09 21:21:26]

Done.

+
+////////////////////////////////
+// NativeCocoaScrollBar
+////////////////////////////////
+
+NativeCocoaScrollBar::NativeCocoaScrollBar(bool horizontal)
+    : NativeScrollBar(horizontal) {}
+
+NativeCocoaScrollBar::~NativeCocoaScrollBar() {}
+
+NativeScrollBarWrapper* NativeCocoaScrollBar::CreateWrapper() {
+  return new NativeCocoaScrollBarViews(this);
+}
+
+////////////////////////////////
+// NativeCocoaScrollBarViews
+////////////////////////////////
+
+NativeCocoaScrollBarViews::NativeCocoaScrollBarViews(
+    NativeScrollBar* native_scroll_bar)
+    : NativeScrollBarViews(native_scroll_bar),
+      animation_(kFadeDurationMs, kFadeFrameRateHz, this) {
+  bridge_.reset([[ViewsScrollbarBridge alloc] initWithDelegate:this]);
+  UpdateScrollStyle();

[tapted, 2016/02/08 00:31:15]

So I think we can simplify things a bit and get a much smoother animation by
using a ui::Layer.

Here, you would call

SetPaintsToLayer(true);

(invoking the method on views::View).

Then

GetLayer()->SetAnimator()->(
    new ui::LayerAnimator(base::TimeDelta::FromMilliseconds(kFadeDurationMs));


(the gfx::LinearAnimation shouldn't be needed)

Then, see other comments.


However, there is a tricky part, and that's what to do with the gutter with
legacy scrollbars -- it shouldn't fade out, but the thumb should (partially).  I
think the best way to do it would be to add the scrollbar thumb as a subview
with its own layer.

[spqchan, 2016/02/09 21:21:26]

Done.

+}
+
+NativeCocoaScrollBarViews::~NativeCocoaScrollBarViews() {}
+
+void NativeCocoaScrollBarViews::AnimationProgressed(
+    const gfx::Animation* animation) {
+  scroller_opacity_ = 1 - animation->GetCurrentValue();
+  SchedulePaint();
+}
+
+void NativeCocoaScrollBarViews::OnScrollerStyleChanged() {
+  UpdateScrollStyle();
+}
+
+void NativeCocoaScrollBarViews::UpdateScrollStyle() {
+  NSScrollerStyle scroller_style = [bridge_ getPreferredScrollerStyle];
+  if (scroller_style_ == scroller_style && init_)
+    return;
+  init_ = true;
+  scroller_style_ = scroller_style;
+  if (scroller_style_)
+    HideScrollbar();
+  else
+    ShowScrollbar();
+}
+
+ui::NativeTheme::OverlayParams NativeCocoaScrollBarViews::GetOverlayParams() {
+  ui::NativeTheme::OverlayParams params;
+  params.is_overlay = true;
+  params.alpha = scroller_opacity_;
+  return params;
+}
+
+bool NativeCocoaScrollBarViews::OnScroll(float dx, float dy) {
+  bool didScroll = BaseScrollBar::OnScroll(dx, dy);
+
+  // If we're using the overlay style, then we should fire the timer
+  if (didScroll && scroller_style_ == NSScrollerStyleOverlay) {
+    ShowScrollbar();
+    if (hide_scrollbar_timer_.IsRunning()) {
+      hide_scrollbar_timer_.Reset();
+    } else {
+      hide_scrollbar_timer_.Start(
+          FROM_HERE,
+          base::TimeDelta::FromMilliseconds(kScrollbarHideTimeoutMs),
+          this,
+          &NativeCocoaScrollBarViews::HideScrollbar);
+    }
+  }
+  return didScroll;
+}
+
+void NativeCocoaScrollBarViews::HideScrollbar() {
+  animation_.Start();

[tapted, 2016/02/08 00:31:15]

Then here, you would just call

GetLayer()->GetAnimator()->SetOpacity(0.0);

You shouldn't need the SchedulePaint call

[spqchan, 2016/02/09 21:21:26]

Done.

+  SchedulePaint();
+}
+
+void NativeCocoaScrollBarViews::ShowScrollbar() {
+  animation_.Stop();

[tapted, 2016/02/08 00:31:15]

And here, 
GetLayer()->SetOpacity(1.0);

[spqchan, 2016/02/09 21:21:26]

Done.

+  scroller_opacity_ = 1.0;
+  SchedulePaint();
+}
+
+}  // end of views namespace