RESOLVED FIXED 100957
[WK1] Fixed-position elements jiggle up and down slightly during scrolling on a Retina display 
https://bugs.webkit.org/show_bug.cgi?id=100957
Summary [WK1] Fixed-position elements jiggle up and down slightly during scrolling on...
Adam Roben (:aroben)
Reported 2012-11-01 07:15:42 PDT
Created attachment 171842 [details] testcase To reproduce: 1. Set your display to a Retina resolution 2. Load the attached test case in WebKit1 3. Scroll up and down a bit The fixed div jiggles up and down slightly while scrolling. This does not happen in WebKit2.
Attachments
testcase (396 bytes, text/html)
2012-11-01 07:15 PDT, Adam Roben (:aroben) 		no flags
Details
Patch (1.92 KB, patch)
2012-11-01 11:25 PDT, Adam Roben (:aroben) 		no flags
DetailsFormatted DiffDiff
Patch (2.77 KB, patch)
2012-11-01 12:02 PDT, Adam Roben (:aroben) 		no flags
DetailsFormatted DiffDiff
Show Obsolete (1) View All Add attachment proposed patch, testcase, etc.
Adam Roben (:aroben)
Comment 1 2012-11-01 07:34:42 PDT
This even happens waaaaaay back in the r37376 nightly build.
Adam Roben (:aroben)
Comment 2 2012-11-01 07:41:14 PDT
The bug gets worse if the fixed-position element has -webkit-transform:translate3d(0,0,0) applied to it. Then it jiggles by two device pixels instead of one.
Beth Dakin
Comment 3 2012-11-01 10:18:00 PDT
Adam Roben!! I could have sworn we fixed this. Simon, did we fix this?
Adam Roben (:aroben)
Comment 4 2012-11-01 10:38:54 PDT
Turning off Settings::setFixedPositionCreatesStackingContext does not fix this.
Adam Roben (:aroben)
Comment 5 2012-11-01 10:51:29 PDT
Simon helped us realize that WebKit2 only scrolls by full pixels, even in Retina mode, while AppKit will scroll by half-pixels in Retina mode. WebCore can only represent full pixels at the moment, so this is probably the source of the bug.
Beth Dakin
Comment 6 2012-11-01 11:07:04 PDT
Ah yes, this is in Radar as <rdar://problem/11244706>
Adam Roben (:aroben)
Comment 7 2012-11-01 11:25:11 PDT
Created attachment 171899 [details] Patch
Simon Fraser (smfr)
Comment 8 2012-11-01 11:27:54 PDT
Comment on attachment 171899 [details] Patch It seems unfortunate to impact the scrolling behavior of every app using WK1, whether or not they have fixed position elements. Maybe this should be opt-in somehow?
Adam Roben (:aroben)
Comment 9 2012-11-01 12:02:31 PDT
Created attachment 171904 [details] Patch
Adam Roben (:aroben)
Comment 10 2012-11-01 12:03:10 PDT
OK, added a new patch that only affects pages with position:fixed or position:sticky elements. It is not currently opt-in. Simon, were you imagining a new preference key? Or some other opt-in mechanism?
WebKit Review Bot
Comment 11 2012-11-01 13:58:09 PDT
Comment on attachment 171904 [details] Patch Clearing flags on attachment: 171904 Committed r133225: <http://trac.webkit.org/changeset/133225>
WebKit Review Bot
Comment 12 2012-11-01 13:58:12 PDT
All reviewed patches have been landed. Closing bug.
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