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<title>[198444] trunk/Source/WebCore</title>
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<dl class="meta">
<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/198444">198444</a></dd>
<dt>Author</dt> <dd>mmaxfield@apple.com</dd>
<dt>Date</dt> <dd>2016-03-18 14:14:41 -0700 (Fri, 18 Mar 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>[OS X] Scrollbars are sometimes erroneously reported as overlay
https://bugs.webkit.org/show_bug.cgi?id=155630
Reviewed by Darin Adler.
When AppKit boots up, if the system preference is set to determine at runtime whether
scrollbars should be overlay or always-on, AppKit must do some processing to determine
this scrollbar state. We listen for the results by using NSScrollerImpPairDelegate's
scrollerImpPair:updateScrollerStyleForNewRecommendedScrollerStyle: method.
However, our NSScrollerImpPairDelegates are owned by the FrameView, and when loading
a page, there is a short amount of time when no FrameViews are alive. This means that
there is a point in time when we don't have any NSScrollerImpPairs alive. Unfortunately,
the processesing that AppKit does to determine the scrollbar state is done
asynchronously, and the results may be reported within this short window. In this case,
we don't receive the notification that the scrollbar should be non-overlay, and our
internal state (gUsesOverlayScrollbars in ScrollbarThemeMac) becomes stale.
The solution is to simply always check what the scrollbar state is upon creation of a
NSScrollerImpPair. That way, as soon as the second FrameView is created, the scrollbar
state will be correctly updated immediately.
An alternative, similar, approach would be for ScrollbarThemeMac to listen to the
NSPreferredScrollerStyleDidChangeNotification. This patch doesn't use this approach
in order to align with the current division of responsibilities between ScrollAnimator
and ScrollbarTheme.
Covered by existing (RTL Scrollbar) tests.
* platform/mac/ScrollAnimatorMac.mm:
(WebCore::ScrollAnimatorMac::ScrollAnimatorMac):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>
<li><a href="#trunkSourceWebCoreplatformmacScrollAnimatorMacmm">trunk/Source/WebCore/platform/mac/ScrollAnimatorMac.mm</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (198443 => 198444)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/ChangeLog 2016-03-18 20:54:50 UTC (rev 198443)
+++ trunk/Source/WebCore/ChangeLog 2016-03-18 21:14:41 UTC (rev 198444)
</span><span class="lines">@@ -1,3 +1,37 @@
</span><ins>+2016-03-18 Myles C. Maxfield <mmaxfield@apple.com>
+
+ [OS X] Scrollbars are sometimes erroneously reported as overlay
+ https://bugs.webkit.org/show_bug.cgi?id=155630
+
+ Reviewed by Darin Adler.
+
+ When AppKit boots up, if the system preference is set to determine at runtime whether
+ scrollbars should be overlay or always-on, AppKit must do some processing to determine
+ this scrollbar state. We listen for the results by using NSScrollerImpPairDelegate's
+ scrollerImpPair:updateScrollerStyleForNewRecommendedScrollerStyle: method.
+
+ However, our NSScrollerImpPairDelegates are owned by the FrameView, and when loading
+ a page, there is a short amount of time when no FrameViews are alive. This means that
+ there is a point in time when we don't have any NSScrollerImpPairs alive. Unfortunately,
+ the processesing that AppKit does to determine the scrollbar state is done
+ asynchronously, and the results may be reported within this short window. In this case,
+ we don't receive the notification that the scrollbar should be non-overlay, and our
+ internal state (gUsesOverlayScrollbars in ScrollbarThemeMac) becomes stale.
+
+ The solution is to simply always check what the scrollbar state is upon creation of a
+ NSScrollerImpPair. That way, as soon as the second FrameView is created, the scrollbar
+ state will be correctly updated immediately.
+
+ An alternative, similar, approach would be for ScrollbarThemeMac to listen to the
+ NSPreferredScrollerStyleDidChangeNotification. This patch doesn't use this approach
+ in order to align with the current division of responsibilities between ScrollAnimator
+ and ScrollbarTheme.
+
+ Covered by existing (RTL Scrollbar) tests.
+
+ * platform/mac/ScrollAnimatorMac.mm:
+ (WebCore::ScrollAnimatorMac::ScrollAnimatorMac):
+
</ins><span class="cx"> 2016-03-18 Jer Noble <jer.noble@apple.com>
</span><span class="cx">
</span><span class="cx"> CRASH in WebCore::MediaResourceLoader::requestResource + 698
</span></span></pre></div>
<a id="trunkSourceWebCoreplatformmacScrollAnimatorMacmm"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/platform/mac/ScrollAnimatorMac.mm (198443 => 198444)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/platform/mac/ScrollAnimatorMac.mm 2016-03-18 20:54:50 UTC (rev 198443)
+++ trunk/Source/WebCore/platform/mac/ScrollAnimatorMac.mm 2016-03-18 21:14:41 UTC (rev 198444)
</span><span class="lines">@@ -630,6 +630,9 @@
</span><span class="cx"> m_scrollbarPainterController = adoptNS([[NSScrollerImpPair alloc] init]);
</span><span class="cx"> [m_scrollbarPainterController setDelegate:m_scrollbarPainterControllerDelegate.get()];
</span><span class="cx"> [m_scrollbarPainterController setScrollerStyle:recommendedScrollerStyle()];
</span><ins>+
+ if (auto* theme = macScrollbarTheme())
+ theme->usesOverlayScrollbarsChanged();
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> ScrollAnimatorMac::~ScrollAnimatorMac()
</span></span></pre>
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