146202 - PNG transparency displayed as black after scrolling

Status: RESOLVED WORKSFORME

(Core Graveyard :: Image: Painting, defect)

Description

[Basil Fritts]

From Bugzilla Helper:
User-Agent: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.0rc3) Gecko/20020520
BuildID:    2002052006-1.0-branch

When the page is first loaded, the PNG transparency displays correctly. After
scrolling down the page, and then scrolling back up, the transparency (the alpha
channel?) is displayed as black.

Reproducible: Always
Steps to Reproduce:
1.load the URL
2.scroll a bit

Actual Results:  Transparency appears black.

Expected Results:  Transparency is transparent.

This PNG was generated using GIMP. the transparency also has some issues in IE
5.5. It is nested in a div that is being absolutely positioned.

This seems really eccentric, and I'm not seeing it elsewhere. I will continue
testing to see what else might be causing the problem.

Comment 1

[Basil Fritts]

Attachment: A screenshot of what I'm seeing.

Comment 2

[Basil Fritts]

This may be related to a similar issue seen in GIFs, logged in bug 96803.

Comment 3

[KS]

I see a bug using build 2002052913, with SVG and MathML on Windows 98SE. Caveat:
I have a page with multiple PNGs with some form of transparency; some work fine,
some don't. What the difference is, I don't know. I created the ones that do
work with batik-1.1.1 from SVG files. (Someday I won't have to; that's another bug.)

The buggy redraw depends on what part of the image was offscreen, and how it is
scrolled to. For example, if the bottom part of the image is visible at the top
of the screen and I scroll back, either jumping a screenful or gradually, I get
black instead of transparency. But if none of the image is visible and I jump
back, I get transparency. However if I scroll back gradually with a drag, I get
black. If the image is below the bottom of the screen and I drag down to it, the
parts that are revealed show black; if I jump, they show transparency.

Comment 4

[Basil Fritts]

KS -- Reporter here:

It has been suggested that this issue may be related to video driver. What
driver are you using for your video card?

Comment 5

[KS]

This appears to overlap with Bug 142395, comment 14.

Machine is a Compaq with Trident Blade 3D/MVP4 (63) OEM card, driver software
version latest from Compaq (Softpaq SP15767), 6.50.5495-69.63icd, of 6-29-2000.
Also checked Trident site, found no driver more recent.

So, if Mozilla doesn't like the driver seems it's up to Mozilla to get over it.

Comment 6

[Nathan Smith]

I have onboard ATI Rage PRO card with the newest drivers and I have this problem
as well.  I have noted the exact same circumstances.  At first I thought I was
seeing things...

Comment 7

[KS]

Using Mozilla 1.1a, build 2002061104, behavior in comment #3 persists.

I still don't know why some PNGs win, some lose, both with transparency.

Comment 8

[Glenn Randers-Pehrson]

This seems to be a dupe of bug 75558.  PNG transparency goes black when
the PNG is being scaled and is OK when the image is unscaled.  The reference
URL has been changed so I can't tell if the PNG was being scaled.  The problem
still exists in Mozilla 1.1b.

Glenn

Comment 9

[Alfred Kayser]

Retest, as it worksforme, 20030408080, W2K.
Can probably be closed.

Comment 10

[pachollini]

It seems this problem was solved in 1.4 but re-appeared in 1.5 RC1 (20030924):
see http://www.webmapy.cz/app/prague-online/app/app.php - you can click and drag
in the map window and a semi-transparent rectangle should be displayed. This
works fine in 1.4 and Firebird 0.6, but not in 1.5RC1.

Comment 11

[Steve VanSlyck]

Some discussion at http://homepage.ntlworld.com/bobosola/pngtest.htm