159893 - IFRAMEs containing PNG images flash black when scrolling

Status: RESOLVED DUPLICATE of bug 163577

(Core Graveyard :: Image: Painting, defect)

Description

[Stuart Wigley]

From Bugzilla Helper:
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.1b) Gecko/20020721
BuildID:    2002072104

I first spotted this problem on the supplied URL, and I have reduced the source
of this page into the attached test case. 

The scenario is that you have a webpage which has an IFRAME containing a PNG
image. The webpage also has a fixed-position, no-repeat CSS background image.
When scrolling this page, the PNG image in the IFRAME
takes a while to redraw, and the result is that the background of the IFRAME
flashes black.

Remove the background image, and scrolling seems to be OK again.

Reproducible: Always
Steps to Reproduce:
1. Open Test Case HTML file (and image)
2. Resize browser window so that scrolling is necessary (optional)
3. Scroll up and down

Actual Results:  Each IFRAME flashes black during scrolling

Expected Results:  Scrolling should be smooth.

Comment 1

[Stuart Wigley]

Attachment: Test Case

Comment 2

[Kai Lahmann (is there, where MNG is)]

worksforme (on Linux), so it's either a ghost or windows only.

Comment 3

[Stuart Wigley]

Yep, I just retested and the same build is fine on Linux. Maybe just Windows?

Comment 4

[Moiz Dohadwala]

build: 2002072908, win2k, sp2. The problem is quite severe for me. It could also
be due to the fact that the IFRAMES have a scroll bar (the png is larger than
the IFRAME?)

-Moiz

Comment 5

[Michael Lefevre]

confirming (1.1beta and 2002072804, both win2k).

dunno if this is the iframes or the images, but I'm guessing the images...

Comment 6

[Thamer Mahmoud]

Attachment: IFrames with fixed backgrounds

Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.1) Gecko/20020824

It's not PNG related. I'm using Windows XP and I'm seeing redraw effects on
*every* IFrame.

It's ugly on fixed backgrounds but it also flickers "less" on other pages. The
flickery rate seems also dependant on how large an IFrame is. It's really
annoying on websites that use IFrames for ads, headers and footers...etc  

I'm including a better test case (two of them, actually) one shows IFrames with
fixed backgrounds and another showing IFrames that flicker around the edges
while scrolling. Use your mouse and scroll bar for scrolling. 

I reported Bug #163577 (a possible DUPL) before finding this one. So Could
someone please change the description/Component because It's not PNG related.

Comment 7

[Thamer Mahmoud]

Attachment: IFrames with flicker around their edges (while scrolling)

Comment 8

[Thamer Mahmoud]

Attachment: IFrames with fixed backgrounds

Comment 9

[David W. Jeske]

I agree with #6 from Thamer. This flickering happens anytime an IFRAME is
resized/refreshed on MS Windows. PNGs probably slow down the scrolling related
refresh enough to cause it to happen during scrolling. However, the problem does
not seem to appear at all on Mozilla/UNIX.

Here is another test case which is much better at reproducing the problem:

http://mozart.chat.net/~jeske/Projects/Mozilla/bugs/4.html

Comment 10

[David W. Jeske]

BTW: when using Thamer's test cases such as "Iframes flicker around their edges
(while scrolling)" it is much easier to see the problem if you turn on "resize
window contents while dragging" and just resize the window. (Again, this only
happens on MS Windows).

Comment 11

[Thamer Mahmoud]

*** This bug has been marked as a duplicate of 163577 ***