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

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=142783

--- Comment #4 from Julien Isorce <j.isorce at samsung.com> ---
Created attachment 248943
  --> https://bugs.webkit.org/attachment.cgi?id=248943&action=review
Example of positionned divs

In the attached exmaple, all the divs become composited (creates a backing), because of the video tag.

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.

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

You can use the attached patched to print info on composited layers.

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.

https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Understanding_z_index/The_stacking_context
https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Understanding_z_index/Stacking_without_z-index

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