224572 - Very slow scrolling on website with large background image

Status: RESOLVED DUPLICATE of bug 90198

(SeaMonkey :: General, defect)

Description

[MORA]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.6a) Gecko/20031102 Firebird/0.7+ (aebrahim)
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.6a) Gecko/20031102 Firebird/0.7+ (aebrahim)

When viewing the page http://www.goddamn.co.uk/tobyink/ with the 'Matrix' page style (select with the stylesheet switcher or via the website's 'site style' menu), scrolling is very slow and jagged. 

Reproducible: Always

Steps to Reproduce:
1. Go to http://www.goddamn.co.uk/tobyink/
2. Activate the Matrix style in the 'site style' menu or via the style switcher
3. Scroll up and down the page

Actual Results:  
Scrolling was smooth and jagged. 

Expected Results:  
Scrolling speed should have been normal and scrolling should have been smooth

I have observed this problem in the latest unofficial build by aebrahim, and confirmed this with the 0.7 milestone release. However, the old 0.6 milestone release for Windows works as expected!

Note: I haven't verified the problem in Mozilla 1.x.

Comment 1

[Paul Shuttle]

There doesn't seem to be any Matrix style on the site you linked to, but this
sounds very similar to http://bugzilla.mozilla.org/show_bug.cgi?id=124150

Comment 2

[MORA]

Apparantly the site owner has taken away the theme (maybe it created bandwidth 
issues; the background image was very large). 

I don't know if the error is really identical to bug 124150, but the symptoms 
surely are. However, it seems like bug 124150 has something to do with the menu's 
on the left (scrolling is better at the end of that page), whereas the 
Matrix-theme problem seems to have been caused by the large background image. 
Notice that the other themes on that site don't yield any problems. 

Very unfortunate that this theme has disappeared before the problem could be 
investigated properly. :(

Comment 3

[MORA]

OK, the Matrix style is back up again. However, the scrolling problem is less 
pronounced this time; it still isn't as smooth as it could be, though. Here's a 
list of changes on the website since my initial report, as reported by the 
website author:

- previously the print style sheet path was hardcoded into the site, 
  now it gets the URL from a database
- the order of how the stylesheets are linked has been rearranged to 
  to get around a nasty Konqueror bug
- a "handheld" media style sheet has been added. 

According to the author, the slowdown was caused by the combination of the huge 
file size, the fixed background and the translucent black layer behind the text;
apparantly Opera suffers from the same problem. 

I hope this additional information can shed some more light on the problem. 

Comment 4

[Wayne Woods]

I can confirm this problem on the Mac version, 20031104 Firebird/0.7+, so
hardware/software could be set to "All".

The scrolling is fine in Safari, so I agree it's most likely a browser bug and
not a bad web page.

However the problem also exists in the standard Mozilla (Seamonkey) browser, so
I wonder if it's just a dupe of bug 90198 (unless the layout code involved has
forked with Firebird?). That bug deals with poor scrolling when the page has a
fixed background image.

Comment 5

[MORA]

In a related thread on MozillaZine
(http://forums.mozillazine.org/viewtopic.php?t=32886), 'Athropos' wrote:

I found what causes this: there is an image called 'semiopaque.png' that is used
as background for DIVs in front of the 'real' background image.

I made a small page to test this: 
http://perso.club-internet.fr/fingelrest/img_forums/SlowTest/SlowTest.html
I used the same 'semiopaque.png'.

I think he is correct; scrolling in his test page is also quite slow.

Comment 6

[Jon Henry]

This is possibly a dupe of bug 90198, or at least it's a contributing factor.
Also potentially related is bug 182102.

Either way, this bug appears in SeaMonkey as well as Firebird, so I'm moving it
to the Browser product.

Comment 7

[Jon Henry]

Attachment: Background for testcase (See below)

Comment 8

[Jon Henry]

Attachment: Semi-opaque image for testcase (see below)

Comment 9

[Jon Henry]

Attachment: Reduced test case

This is more or less a copy of the website mentioned above (minus some
advertising code his ISP tacked on it looks like), in case it goes down for any
reason. As you can see, scrolling is choppy.

Comment 10

[MORA]

Here's another page that suffers from slow scrolling: 
http://weblogs.mozillazine.org/djst/archives/004300.html

The root-page: http://weblogs.mozillazine.org/djst/ works fine though; the slow
scrolling is noticeable only on the 'comments' pages in this weblog (the page in
question contains a nice example, as the comments there have lead to a flame war :).

I have verified this with Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US;
rv:1.6b) Gecko/20031117 Firebird/0.7+ (aebrahim), and K-Meleon 0.8, so I guess
this is actually a Gecko bug, not a Firebird bug. Scrolling is smooth in Opera
7.22, so it is not a coding problem of the webpage.

Comment 11

[TGOS]

For me 
http://weblogs.mozillazine.org/djst/archives/004300.html
and The root-page:
http://weblogs.mozillazine.org/djst/
are almost equally fast. I mean, the second page is very large (much more
content on the page), so of course it's supposed to be slower.

However, the Matrix Style page makes me wonder. Using Matrix Style on this page:
http://www.goddamn.co.uk/tobyink/
makes scrolling indeed a lot slower and causes 100% CPU load. No matter if
smooth scrolling is enabled or not. Comparing that to IE 6.0, IE 6.0 does a much
better job (even though smooth scrolling looks ugly with Matrix Style,
performance is not so much worse compared to the default style).

I've seen poor scrolling on many other pages. I have an example on my HD where
Mozilla/Firebird and the other ones scroll horribly slow (it takes almost 10
seconds to scroll down one page, once you clicked on the scroll bar... onn a 1
GHz machine!!!) and where IE scrolls lightning fast, but I don't know if I can
present it to the public (it's part of an online game, that is totally browser
based). 

If you scroll the map there, which has no large background image (195 x 195) and
also no larger image in the foreground, Mozilla gets awfully slow. And not just
scrolling gets slow, switching from the tab to another one and switching from
another one to that one causes 90% CPU load and causes Mozilla to stop reacting
for 2 seconds. I found out, however, that altering the backround image from
"fixed" to a scrollable one decreases the effect dramatically (even though
Mozilla is *still* slow afterwards) and the Matrix Style also has a fixed
background image, so this may cause the problem here.

Comment 12

[Jon Henry]

I'm confident enough that this is a dupe of bug 90198. If someone disagrees, or
that bug gets fixed and this page remains painfully slow, feel free to reopen or
discuss it here.

*** This bug has been marked as a duplicate of 90198 ***