[Webkit-unassigned] [Bug 86896] background elements render poorly below foreground content

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=86896





--- Comment #2 from Mike Sierra <mike.sierra at nokia.com>  2012-05-22 09:51:00 PST ---
I spawned a few simplified pages, the various "_render" pages posted
here:

  http://letmespellitoutforyou.com/t/

Again, in all these cases, the bottom-most displaying element is the
gray list that contains the song titles.

When trimming the number of list items, I noticed a relevant variable.
All of these pages DO NOT display the rendering bug when the browser
screen is large and there's plenty of clearance on the bottom. The
relevant pages DO display the bug when you first do the following:

1. Resize the window so that the bottom-right corner roughly aligns
   with the bottom-right of the last list item ("Hot Cakes")

2. Scroll to the bottom of the page

3. If necessary, reload.

These pages tried to isolate various page-redraw scenarios, built as
follows:

_render1: CSS places background-image directly in bottom margin gutter

_render2: initial CSS places same img above screen; load handler
applies alternate CSS class that places img in bottom margin gutter
using background-position CSS

_render3: same as #2, but 2-second timeout before alternate CSS
applies

_render4: same as #3, but additional CSS transition

_render5: same as #4, but NO timeout delay, and YES animated
transition

Nightly build displays rendering artifacts for cases #3-#5, all of
which involve some combination of delays before image's final position
renders.

The animating examples display additional rendering artifacts
when you scroll during the transition's progress.

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