[Webkit-unassigned] [Bug 142783] RenderLayerCompositor: only create backing for visible and non-empty layers

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Wed Mar 18 11:28:52 PDT 2015


--- Comment #6 from Simon Fraser (smfr) <simon.fraser at apple.com> ---
(In reply to comment #4)
> Created attachment 248943 [details]
> Example of positionned divs
> In the attached exmaple, all the divs become composited (creates a backing),
> because of the video tag.

Not on Mac. I get one big layer for the rootmost view and none inside of it.

> If the video tag is added after all the divs or in a zindex different than 0
> then all the divs do not become composited.

Odd that there's an ordering difference.

> So is it really an expected behaviour  for neasted divs to all become
> composited this way ?

No. Are you testing webkit TOT?

> About stacking context the following doc is very helpful:
> "When no z-index property is specified, elements are rendered on the default
> rendering layer 0 (zero)." , but if I put 0 manually the divs do not become
> composited (if I put auto they become composited)
> "A stacking context is formed, anywhere in the document, by any element
> which is positioned (absolutely or relatively) with a z-index value other
> than "auto" "
> It seems to behave the opposite as said juste before.

z-index:0 create stacking context, but has z-index 0 in its parent stacking context. z-index: auto does not create stacking context.

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