155371 - Form elements may cause transparent PNG to disappear

Status: RESOLVED WORKSFORME

(Core :: Layout, defect, P4)

Description

[Adrian Ulrich]

1) Open Mozilla and open two tabs (the problem also appears without tabs, but
it's easy to reproduce with tabs..)

2) In tab 1, load:
http://www.blinkenlights.ch/cgi-bin/medi/gif.pl?action=fc
Switch to tab 2 and back to 1.. page looks still okay

3) in tab 1 load:
http://www.blinkenlights.ch/cgi-bin/medi/gif.pl
Switch to tab 2 and back to 1.. still okay..

4) in tab 1 load:
http://www.blinkenlights.ch/cgi-bin/medi/png.pl?action=fc
To tab 2 and back.. everything is okay (The red bar is now a transparent blue png..)

Now:
5) in tab 1 load
http://www.blinkenlights.ch/cgi-bin/medi/png.pl

-> The blue bar doesn't appear
Switching to tab 2 and back to 1 may display the image..
..Marking text (Super Medipage) may display some parts of the image..

The only difference between 'png.pl' and 'png.pl?action=fc' is, that the
'png.pl' has a form element..

Build 2002063023 on PPC Linux
Seems to work well on Mac os X

(This isn't an imglib bug, is it?)

Comment 1

[Ben Tobin]

I've noticed this problem as well if a <div style="position: fixed"> with a
transparent PNG gets collides with a form element when scrolling the page.  The
transparent PNG will disappear temporarily as it passes over the form element,
then reappears.  

I've only noticed this behavior in Linux.  I haven't seen it in any of the
versions I use in windows.  

I can't give an example url right now since the only place I've seen this bug is
on one of my site's password-protected maintainance pages.  I can make a static
copy and supply a link if necessary.  Let me know.

Comment 2

[Jonas Koch Bentzen]

I can confirm the problem (tested in Mozilla 1.2b on Linux): If you have a fixed
element with a background which is a transparent/semi-transparent PNG image and
you scroll past certain form elements, the fixed element disappears. The problem
seems to apply to select boxes and buttons (submit, reset, button) only - i.e.,
text input fields, radio buttons, checkboxes, and textareas don't have that
problem. See the attached HTML page for an example.

Comment 3

[Jonas Koch Bentzen]

Attachment: HTML test page (also download the PNG)

Comment 4

[Jonas Koch Bentzen]

Attachment: PNG image

Comment 5

[Boris Zbarsky [:bzbarsky]]

Attachment: testcase that you can just load

Comment 6

[Boris Zbarsky [:bzbarsky]]

This worksforme in a current Linux trunk build; a lot of the code involved has
changed since this bug was filed.... If this _is_ still a problem, please reopen
and post a testcase.