RESOLVED CONFIGURATION CHANGED206024
Thin line sometimes shown above heading on twitter.com 
https://bugs.webkit.org/show_bug.cgi?id=206024
Summary Thin line sometimes shown above heading on twitter.com
Kenneth Kufluk
Reported 2020-01-09 12:23:30 PST
Created attachment 387254 [details] Screenshot of Twitter on my iPad showing the line at the top of the site. Hi. I'm a web engineer on twitter.com. I have found an infrequent rendering bug when using iPhone or iPad with mobile.twitter.com. I use dark mode on the OS and on twitter. I scroll my home timeline. When scrolling stops, I sometimes see one pixel of rendering from the timeline under the top header, appearing above the header. This is most apparent when there is a bright image in the timeline. This bug either does not appear, or is much less apparent, when the phone is not in dark mode. I suspect it is less apparent. I have made a reduced test case here: https://clumsy-biplane.glitch.me (make sure your phone is in dark mode) The bug appears far less frequently in the reduced test case. Perhaps 20-30 scrolls up and down might be needed. I find the line only appears after the scroll moment has finished. By comparing screenshots, I believe the line is an additional line, because I measured an extra 1px between the top of the screen and the text in the header.
Attachments
Screenshot of Twitter on my iPad showing the line at the top of the site. (1010.35 KB, image/png)
2020-01-09 12:23 PST, Kenneth Kufluk 		no flags
Details
View All Add attachment proposed patch, testcase, etc.
Simon Fraser (smfr)
Comment 1 2020-01-09 12:41:57 PST
Probably a rounding error in the positioning of the position:fixed header. Does the patch have a meta viewport that gives it unit scale (width=device-width)?
Kenneth Kufluk
Comment 2 2020-01-09 13:04:00 PST
Yes, reduced test case has <meta name="viewport" content="width=device-width, initial-scale=1"> Site has <meta name="viewport" content="width=device-width,initial-scale=1,maximum-scale=1,user-scalable=0,viewport-fit=cover" />
Radar WebKit Bug Importer
Comment 3 2020-01-09 23:38:34 PST
<rdar://problem/58471889>
Karl Dubost
Comment 4 2024-05-02 01:32:41 PDT
@Kenneth, Spring Cleaning. I don't seem to be able to reproduce this issue.
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