38033 - High CPU usage for malformed animated gifs in the left column cause Mozilla to use too much CPU [in 2000 this is 20-30%, in 98/linux it seems to be much worse]

Status: VERIFIED DUPLICATE of bug 36785

(Core :: Graphics: ImageLib, defect, P3)

Description

[timeless]

2000050215 win32-talkback on windows2000
also described on win98 and linux

Loading this page [and leaving it open] results i cpu usage well above the 
normal 0% [windows2000], opening it in the mozilla composer (and closing the 
browser view) and then deleting the left images (in composer) will restore 
normal cpu usage, deleting some of the images and scrolling the window 
offscreen also seems to work (not as well).

while the images are present the caret blinks VERY fast.
In composer, the images draw strangely [especially Selecting some of these 
images in composer results in strange drawing.

The images involved are poorly designed and have two frames, the first frame is 
the complete image, the second is a smaller overlay of the text w/ a 
transparency [white].

I'm guessing that the second [and final] frame of a smaller size is triggering 
reflow.  

explicitly declared image dimensions do not improve the situation.

This also occurs on Netscape 4.72, but not on IE5.5 [which loads the page w/o 
any cpu usage penalty].

The gifs appear to have been generated by the gimp.

Comment 1

[timeless]

Images are set to repeat forever and advanced frame every 100ms.

Comment 2

[Hervé Renault]

i've made some backtraces in gdb (on linux) after stopping mozilla when the CPU
usage was 100%. see the following attachment.

Comment 3

[Hervé Renault]

Attachment: some backtraces in gdb. i stopped mozilla when CPU usage was at 100%

Comment 4

[Hervé Renault]

Attachment: local of the page showing the problem, in case it becomes unavailable.

Comment 5

[pnunn]

Thanks much for the backtraces.
The problem is most severe on unix and a few engineers
are looking into it. The most current theory is that 
nsImage is reused for subsequent frames in the animations
rather than creating new ones. For a short animation loop,
it may be more useful to create a new nsImage for each frame
and keep them around while the animation is running.

There are some bugs that are related to this issue. I may group
them in to one large bug.

and thanks for helping track down this problem.
-P

Comment 6

[Hervé Renault]

Attachment: local copy of the suspect animated GIF (in case it becomes unavailable)

Comment 7

[Hervé Renault]

better : here's a complete copy of the original page (with all the images) at
http://altern.org/mozillazine/bugs/38033/www.sucs.swan.ac.uk_staff_elect.html

Comment 8

[neeti]

moving to m18

Comment 9

[Gagan]

Hmmm... Pam is this a dup of bug 36785?

Comment 10

[timeless]

I'm not sure if it is a dupe, but as I can't see where on that bug I would go 
to reproduce, I would suggest that bug 36785 be marked a dupe of this one if 
someone decides there is duplication.

bug 47212 might be related too.

Comment 11

[Hervé Renault]

altern.org has been shut down.

the new url for the copy of the site is now :

http://mozillazine-fr.org/bugs/38033/www.sucs.swan.ac.uk_staff_elect.html

Comment 12

[Gagan]

*** This bug has been marked as a duplicate of 36785 ***

Comment 13

[Sitsofe Wheeler]

If this bug is going to be duped on bug 36785, please make sure that the 
platforms and OSes are set to all...

Comment 14

[Paul Wyskoczka]

Verified