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Date: Sun, 28 Jun 2009 08:44:23 -0400
From: Charles Wilson <cygwin AT cwilson DOT fastmail DOT fm>
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To: cygwin AT cygwin DOT com
Subject: Re: [RFC] jpeg library
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Yaakov (Cygwin/X) wrote:
> On 28/06/2009 01:17, Charles Wilson wrote:
>> Nope. Upstream development is DEAD.  There was some flurry of activity
>> about two years ago, but it never went anywhere.   If IJG's libjpeg
>> wasn't so widespread and widely used, I'd want to look at some other
>> library that supports the format...
> 
> Actually, are you sure about that?  http://www.ijg.org/ lists a version
> 7, released yesterday, as the current version.

WTH?  You're kidding me...I'm floored.  There's a private mailing list
(with no online archives, natch) for the IJG project, but my
subscription is with an different email account, so I haven't checked it
in a while...nope, no activity on THAT list recently.  Maybe there's a
new list?

Anyway, wow.  OK, this changes things...

From the (competing?) libjpeg on sourceforge, there was a conversation
earlier this week, involving Guido Vollbeding (current IJG jpeg
maintainer), Tom Lane (previous IJG jpeg maintainer), and Bob
Friesenhahn (sourceforge libjpeg maintainer, GraphicsMagick).  Guido said:

> I have taken great care that v6b can be replaced seamlessly with v7,
> and even v8 will remain API compatible while introducing essential
> novelties.

BUT...they went ahead and changed the library version number anyway. In
the sourceforge code (on which cygwin's current jpeg is based), it was
-version-info=62.  In the new jpeg-v7 code, it is -version-info=7:0

In effect, this represents a change from "cygjpeg-62.dll" to
"cygjpeg-7.dll".  Given the speed of jpeg development, I doubt any of us
will be alive when the new DLL number series gets up to 61 (at over 10
years per major number...it'll be 2549 A.D. before we get there).

In that same conversation, there is a lot of mention of the use of
symbol versioning as the panacea for all possible version conflicts.
Nobody has seemed to point out that it works only on ELF systems.

Looks like jpeg-7 incorporates a number of the Debian patches, and many
of the patches from jpegclub.org, so that's good (Hmmm. Actually, the
jpegclub.org website has been updated and now claims
"JPEGclub.org...maintains the Independent JPEG Group's (IJG) software.".
I guess this isn't surprising, as jpegclub.org has always been Guido
Vollbeding's site; now that he's taken over from Tom Lane officially,
this only makes sense).

So, to sum up: ORDINARILY, the new jpeg library should be binary
compatible (and definitely API compatible) with the old one.  It has
lots of new functionality, but in a backwards-compatible way.  However,
they changed the SONAME anyway, which gives us the perfect opportunity
we're looking for.

OK...new plan:  jpeg-v7 will be released for cygwin-1.7 only, using
gcc4/dw2/shared-libgcc only, and will have the name "cygjpeg-7.dll".  It
will NOT have lossless jpeg support.

I'll do this soon.

--
Chuck


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