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/compositor/layer.h"
+#include "ui/compositor/layer_animator.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.
+const int kScrollbarHideTimeoutMs = 300;
+
+// How long animations should take by default.
+const int kFadeDurationMs = 120;
+}

[tapted, 2016/02/11 08:46:18]

nit: blank line before

[spqchan, 2016/02/13 01:39:23]

Done.

+
+////////////////////////////////
+// NativeCocoaScrollBar
+////////////////////////////////

[tapted, 2016/02/11 08:46:17]

The convention in views seems to be more commonly like

////////////////////////////////////////////////////////////////////////////////
// NativeCocoaScrollBar

for these. See e.g native_scroll_bar_views.cc and widget.cc

[spqchan, 2016/02/13 01:39:23]

Done.

+
+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) {
+  bridge_.reset([[ViewsScrollbarBridge alloc] init]);
+  [bridge_ setDelegate:this];
+
+  scroller_style_ = [bridge_ getPreferredScrollerStyle];
+
+  SetPaintToLayer(true);
+  layer()->SetOpacity(scroller_style_ == NSScrollerStyleOverlay ? 0.0 : 1.0);
+  layer()->SetAnimator(new ui::LayerAnimator(
+      base::TimeDelta::FromMilliseconds(kFadeDurationMs)));
+}
+
+NativeCocoaScrollBarViews::~NativeCocoaScrollBarViews() {
+  [bridge_ setDelegate:nullptr];
+}
+
+void NativeCocoaScrollBarViews::OnScrollerStyleChanged() {
+  NSScrollerStyle scroller_style = [bridge_ getPreferredScrollerStyle];
+  if (scroller_style_ == scroller_style)
+    return;
+
+  scroller_style_ = scroller_style;
+  if (scroller_style_)
+    HideScrollbar();
+  else
+    ShowScrollbar();
+}
+
+bool NativeCocoaScrollBarViews::OnScroll(float dx, float dy) {

[tapted, 2016/02/11 08:46:17]

we also need to prevent the scroller fading out while it's being dragged.. 
(more ideas to borrow from OverlayScrollBar)

[spqchan, 2016/02/13 01:39:23]

OverlayScrollBar is a bit different since it shows the scroller when the mouse
is inside the scrollview.
I played around for a bit and got it to work using MouseEnter and MouseExit
handlers on the scrollbar thumb.

I'm considering on setting OnThumbStateChanged in BaseScrollBar to virtual and
then overriding instead though, since doing so might give us something a bit
cleaner.

+  bool didScroll = BaseScrollBar::OnScroll(dx, dy);

[tapted, 2016/02/11 08:46:18]

didScroll -> did_scroll

[spqchan, 2016/02/13 01:39:23]

Done.

+
+  // 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() {
+  layer()->GetAnimator()->SetOpacity(0.0);

[tapted, 2016/02/11 08:46:18]

confusingly, I discovered that  layer()->SetOpacity always goes through the
animator, so the GetAnimator() bit here is redundant. Unfortunately it also
means that when we *show* the scrollbar it's also using an animator. So I think
we need to do (in both Hide and Show)

layer()->GetAnimator()->SetTransitionDuration(base::TimeDelta() or
base::TimeDelta::FromMilliseconds(kScrollbarHideTimeoutMs));

it also means the layer()->SetAnimator call in the constructor is obsolete,
since the first call to GetAnimator creates one with a zero-duration
automatically

[spqchan, 2016/02/13 01:39:23]

Heads up, SetTransitionDuration was private so I had to expose it.
I considered setting the animator each time Show/Hide gets called, but it
doesn't seem efficient

+}
+
+void NativeCocoaScrollBarViews::ShowScrollbar() {
+  layer()->SetOpacity(1.0);
+}
+
+}  // namespace views