Bug 114825 - Garbage at the top of http://www.technologyreview.com after scrolling
Summary: Garbage at the top of http://www.technologyreview.com after scrolling
Alias: None
Product: WebKit
Classification: Unclassified
Component: Layout and Rendering (show other bugs)
Version: 528+ (Nightly build)
Hardware: Unspecified Unspecified
: P2 Normal
Assignee: Simon Fraser (smfr)
URL: http://www.technologyreview.com
Keywords: InRadar
Depends on:
Reported: 2013-04-18 13:16 PDT by Simon Fraser (smfr)
Modified: 2013-04-24 18:26 PDT (History)
7 users (show)

See Also:

Patch (5.39 KB, patch)
2013-04-24 18:18 PDT, Simon Fraser (smfr)
thorton: review+
Details | Formatted Diff | Diff

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Description Simon Fraser (smfr) 2013-04-18 13:16:28 PDT
http://www.technologyreview.com shows garbage at the top on Mac if you scroll down then back up. Regression from r146531
Comment 1 Simon Fraser (smfr) 2013-04-18 13:16:52 PDT
Comment 2 Simon Fraser (smfr) 2013-04-24 17:55:07 PDT
The element showing the garbage pixels has visibility:hidden, which is not considered by RenderLayer::backgroundIsKnownToBeOpaqueInRect().

Another change I notice that affects this is https://bugs.webkit.org/show_bug.cgi?id=108118. Before that revision, we'd compute that the fixed position element is a simple container layer (yellow border). After that change, it became something that draws content.

I haven't been able to make a useful reduction. Most of the time, visibility:hidden just causes us to not parent the compositing layer.
Comment 3 Simon Fraser (smfr) 2013-04-24 18:18:27 PDT
Created attachment 199573 [details]
Comment 4 Tim Horton 2013-04-24 18:22:39 PDT
Comment on attachment 199573 [details]

View in context: https://bugs.webkit.org/attachment.cgi?id=199573&action=review

> LayoutTests/compositing/contents-opaque/visibility-hidden.html:49
> +    	<nav> 
> +			<ul>
> +				<li>Some text here</li>
> +			</ul>
> +    	</nav> 

Comment 5 Simon Fraser (smfr) 2013-04-24 18:26:50 PDT