647494 - z-index changes behaviour with CSS tranform

Status: RESOLVED WORKSFORME

(Core :: General, defect)

Description

[Zéfling]

User-Agent:       Mozilla/5.0 (Windows NT 5.2; WOW64; rv:2.2a1pre) Gecko/20110402 Firefox/4.2a1pre
Build Identifier: 

I presume that the ancient behaviour was okay. See following test:

Reproducible: Always

Comment 1

[Zéfling]

Attachment: z-index with transform

Comment 2

[Zéfling]

Attachment: z-index without transform

Comment 3

[Boris Zbarsky [:bzbarsky]]

http://www.w3.org/TR/css3-2d-transforms/#introduction says:

  Any value other than ‘none’ for the transform results in the creation of both a
  stacking context and a containing block.

so the behavior you see is correct as far as I can tell.

Comment 4

[Boris Zbarsky [:bzbarsky]]

Er, wrong resolution.

Comment 5

[Zéfling]

Okay, the behavior of Presto is similar, but Gecko 1.9.x et Webkit are a behavior different.
It is strange to see like that with floating ojects.

Comment 6

[Zéfling]

Oups, sorry, it's only with Webkit.

Comment 7

[Boris Zbarsky [:bzbarsky]]

I filed https://bugs.webkit.org/show_bug.cgi?id=57730

Comment 8

[Robert O'Callahan (:roc) (email my personal email if necessary)]

I think that creating a stacking context is not enough for z-index to apply. For example, z-index does not apply to an element with opacity:0.5 but position:static.

Comment 9

[Boris Zbarsky [:bzbarsky]]

OK.  Note that Opera, IE9, and we all apply z-index to transformed content (presumably because the spec says it needs to act like position:relative).

I guess we should see where the discussion on www-style ends up.

Comment 10

[Zéfling]

The problem is no longer present.