Bug 100957

Summary:

[WK1] Fixed-position elements jiggle up and down slightly during scrolling on a Retina display

Product:

WebKit

Reporter:

Adam Roben (:aroben) <aroben>

Component:

Layout and Rendering

Assignee:

Adam Roben (:aroben) <aroben>

Status:

RESOLVED FIXED

Severity:

Normal

CC:

andersca, bdakin, dbates, simon.fraser, webkit.review.bot

Priority:

Keywords:

InRadar

Version:

528+ (Nightly build)

Hardware:

Mac (Intel)

OS:

OS X 10.8

Attachments:

Description	Flags
testcase	none
Patch	none
Patch	none

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	Details Formatted Diff Diff
Patch (2.77 KB, patch) 2012-11-01 12:02 PDT, Adam Roben (:aroben)	no flags	Details Formatted Diff Diff
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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