268111 - [FIX]position: fixed elements are positioned relative to the page rather than the viewport

Status: RESOLVED FIXED

(Core :: Layout: Positioned, defect, P5)

Description

[James Ross]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.7.5) Gecko/20041106 Firefox/1.0
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.7.5) Gecko/20041106 Firefox/1.0

When loading a page with a position: fixed element on it (see the URL), the
element is positioned against the page itself, rather than the viewport - even
though it is anchored to the viewport when you scroll.

Reproducible: Always
Steps to Reproduce:
1. Load the URL.
2. Scroll down.
3. Reload (not shift-reload, as that resets the scorll-position). You can also
just resize the window for this step.

Actual Results:  
The position: fixed header vanishes.

Expected Results:  
The position: fixed header should still be anchored to the top-left of the viewport.

It appears to be positioning the fixed element against the page, so if you only
scroll down 1 line and then resize/reload the position: fixed element is then
locked partially off the top of the viewport.

Each time a reflow occurs (reload or resize window) the element is re-anchored
based on the scroll position of the page.

This bug is currently causing ChatZilla to not have any header boxes, as they
use position: fixed (that's how I found it :) ).

Comment 1

[James Ross]

This regression is pretty recent, I believe, as I have only noticed it the past
couple of days - it happens on my 2004110603 build, and CTho's 20041104 build,
but (for reference) not Firefox 1.0 branch. I'm going to try to get some nightly
builds now, but my initial guess is that it's regressed in the past week or two
at most.

Comment 2

[James Ross]

2004-11-01-06 is OK.
2004-11-03-07 is OK.
2004-11-04-07 is broken.

(Windows zip builds from ftp.mozilla.org)

http://bonsai.mozilla.org/cvsquery.cgi?treeid=default&module=all&branch=HEAD&branchtype=match&dir=&file=&filetype=match&who=&whotype=match&sortby=Date&hours=2&date=explicit&mindate=2004-11-03+05%3A00&maxdate=2004-11-04+07%3A00&cvsroot=%2Fcvsroot

The check-in for bug 266968, at 2004-11-03 08:16, would seem a likely place to
start looking.

Comment 3

[James Ross]

CCing bz since his bug looks related.

Comment 4

[Boris Zbarsky [:bzbarsky]]

The problem is that the CSS specification is somewhat self-contradictory here.

1)  The fixed-position div should not move when we scroll.
2)  Since it has auto top and bottom, its position depends on where it would
    show up if it were statically positioned.
3)  Where it would show up if statically positioned depends on the scroll
    position.

Note that before the checkin for bug 266968 we mishandled scrolling when
calculating static positions.  So the testcase in this bug rendered
consistently, but absolutely positioned divs wouldn't render right if things got
scrolled.  Now we account for the scroll position correctly, and this bug results.

I've sent mail to [e-mail] regarding this inconsistancy... let's see
what they say.  Taking, I guess.

As for Chatzilla, I recommend specifying some offsets.  You might want to file a
separate bug on that.

Comment 5

[Boris Zbarsky [:bzbarsky]]

The mail I sent is at
http://lists.w3.org/Archives/Public/www-style/2004Nov/0031.html

Note that my proposed changes to the spec to remove the contradiction will
probably leave chatzilla broken if implemented.

Comment 6

[Hixie (not reading bugmail)]

Replied: http://lists.w3.org/Archives/Public/www-style/2004Nov/0032.html

Comment 7

[James Ross]

Ah, it turns out it was only my custom output window that lacked a top property
for the header in ChatZilla - the built-in one does specify top: 0px and is thus
not affected by this change in behaviour.

Comment 8

[Frank Wein [:mcsmurf]]

*** Bug 273177 has been marked as a duplicate of this bug. ***

Comment 9

[Boris Zbarsky [:bzbarsky]]

*** Bug 276154 has been marked as a duplicate of this bug. ***

Comment 10

[Boris Zbarsky [:bzbarsky]]

Attachment: Fix

This restores the old behavior of using the static position with all scrollable
things scrolled to default position.... I suspect we do want to keep backwards
compat here, unfortunately.  :(

Comment 11

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

Comment on attachment 170755 [details] [diff] [review]
Fix

r+sr=dbaron (assuming you're restoring old code, didn't really look)

Comment 12

[Christian :Biesinger (don't email me, ping me on IRC)]

Attachment: testcase

attaching testcase from URL here so it won't get lost

Comment 13

[Boris Zbarsky [:bzbarsky]]

Yes, this is restoring the old code.  Checked in for 1.8b.

Comment 14

[James Ross]

This bug is back again on trunk (not in FF 1.5). Reopen or new bug?

New testcase: http://silver.warwickcompsoc.co.uk/temp/pos_fixed_jump.html

Comment 15

[Boris Zbarsky [:bzbarsky]]

New bug, and please cc me.  But that URL gives me a 503; please attach a testcase to the bug you file?

Comment 16

[James Ross]

Filed bug 331729 and broke the knee-caps of the guy admining the server. ;)