1158666 - absolutely positioned elements with fragmented containing blocks are positioned relative to the first fragment instead of a coordinate system spanning all fragments

Status: UNCONFIRMED

(Core :: Layout, defect)

Description

[Lea Verou]

See [css3-break] for an explanation of why this is a bug. IE/Blink/WebKit all render this correctly. Gecko seems to use the first fragment regardless of where the positioned element is.

[css3-break]: http://www.w3.org/TR/css3-break/#transforms

Comment 1

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Clearer description of bug (since it took me a bit to figure out what you were talking about):

Steps to reproduce:
 Look at dark grey bars in http://result.dabblet.com/gist/36d645b3dec44fcbf6f0

Expected results:  Dark gray bars are at the start and end of each green box, including when the green box is split across columns.

Actual results: Dark grey bars are at the start and end of the first fragment of each green box.



My comments:

What css-break says here is this:
=====
 Absolute positioning affects layout and thus interacts with fragmentation. Both the coordinate system and absolutely-positioned boxes belonging to a containing block will fragment across pages in the same fragmentation flow as the containing block.

 UAs are not required to correctly position boxes that span a fragmentation break and whose before edge position depends on where the box's content fragments. UAs with memory constraints that prevent them from manipulating an entire document in memory are not required to correctly position absolutely-positioned elements that end up on a previously-rendered page.
=====

I thought we had an existing bug on this, but I can't find it.  It's probably hard to do.

Comment 2

[Lea Verou]

Thanks David, sorry for being too lazy/tired myself to make a proper bug report!

Comment 3

[Lea Verou]

Btw “Expected results” should be: Dark gray bars are at the start and end of the green box (fragment) that contains the corresponding element (i.e. not every green box, that’s not what the other UAs do!)

Comment 4

[Boris Zbarsky [:bzbarsky]]

We have a bug for this for inlines broken across lines: bug 489100

I'm not aware of an existing bug for columnsets...