489564 - Regression: GIF image contents tiled right within image transparent area

Status: RESOLVED DUPLICATE of bug 488685

(Core :: Graphics: ImageLib, defect)

Description

[Helder "Lthere" Magalhães]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.0.9) Gecko/2009040821 Firefox/3.0.9 (.NET CLR 3.5.30729)
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2a1pre) Gecko/20090421 Minefield/3.6a1pre

For some GIF images containing a (large enough) surrounding portion of transparent space, image contents appear (unexpectedly) tiled on the right. It's not yet certain which are the GIF generation conditions which trigger the behavior...

Reproducible: Always

Steps to Reproduce:
1. Open a GIF (static: bug's URL [1]; animated: [2]) containing a transparent area on the right;
Actual Results:  
Image content (non-transparent image area) is tiled on the right.

Expected Results:  
Image contents would float over the transparent area, without the artificial time (i.e., displayed previous Firefox version and/or as seen in other browsers and/or image editors).

This erratic behavior can be related with bug 485727 and (regarding the regression scope) bug 411627 also.

Without checking, from memory I'd say the regression range is about a couple of weeks (at least, this was about the first time I noticed). Also, I haven't checked if this is affecting 1.9.1 branch (Firefox 3.5betaX) nor if this is platform-dependent, so feedback would be welcome!


Workaround:
Although somehow off-topic, a possible workaround is using PNG transparency instead: even though old (IE6-) IE versions don't properly support it, 8 bit PNG (256 color palette, more or less equivalent to GIF) seems [3] to do the trick and is a (neat) graceful degradation alternative. ;-)


[1] http://demo.qooxdoo.org/0.7.4/demobrowser/resource/demobrowser/image/method_public18.gif
[2] http://home.att.net/~kidradd/rpower.gif
[3] http://www.sitepoint.com/blogs/2007/09/18/png8-the-clear-winner/

Comment 1

[Helder "Lthere" Magalhães]

Attachment: Screenshot for [1] (comment 0)

Comment 2

[Helder "Lthere" Magalhães]

Attachment: Screenshot for [2] (comment 0)

Comment 3

[Helder "Lthere" Magalhães]

Attachment: Test case created using GIMP

I was able to fabricate a test case using GIMP (2.6.6). The trick seems to be:
1. Create an image with an initial canvas size and transparent background;
2. Draw something within the canvas;
3. Enlarge the canvas (menu "Image", option "Canvas Size...";
4. Save as GIF.

While trying to export to PNG to check for an identical PNG regression, GIMP displayed an interesting message: "PNG plug-in can't handle layer offsets, size or opacity". This has good and (potentially) bad news:
 * Good: hints towards potential underlying issues (likely layer offset;
 * Bad: mean that PNG may be affected also (the GIMP plug-in wasn't able to export these features, doesn't mean that PNG itself doesn't support them).

(Note that I wasn't able to create any test case using Paint .NET (3.36).)

Comment 4

[John P Baker]

This is extremely likely to be bug 488685 - please check again on today's nightly.

WFM on
Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.9.1b4pre) Gecko/20090422 Shiretoko/3.5b4pre ID:20090422042031

Comment 5

[Helder "Lthere" Magalhães]

(In reply to comment #4)
> This is extremely likely to be bug 488685 - please check again on today's
> nightly.

Great, thanks for the hint! ;-)

I did have a look into that issue but didn't though it was much related to this behavior. Assuming you are right and marking as a dup. The testcase can be of use, though (for a potential inclusion in bug 411627). :-)

Verified to be working (again) in:
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2a1pre) Gecko/20090422 Minefield/3.6a1pre