[Pan-users] Re: Previews gone screwy

[Greg Lee]

On Sat, 20 Oct 2007 17:07:14 +0000, walt wrote:

> On Fri, 19 Oct 2007 23:39:25 -0400, Dave Chand wrote:
> 
>> On Oct 6, 2007, at 6:58 PM, Greg Lee wrote:
>> 
>>> I looked at some other 1 part images in this same newsgroup and found
>>> that all those with byte size <= 369052 displayed correctly, but all
>>> those with byte size >= 369361 displayed incorrectly...
> 
>> I have been experimenting with gdk-pixbuf. What I find is the
>> following: in the file gtk+2.12.x/gdk-pixbuf/io-jpeg.c there is the
>> statement #define JPEG_PROG_BUF_SIZE 65536
>> if you change its value to something significantly higher, such as
>> #JPEG_PROG_BUF_SIZE 500000
>> then it seems the decoding problems go away.
> 
> I just sent this question to Matthias Clasen, who increased that number
> from 4096 back in 2002.  It seems that a pixbuf sets an arbitrary size
> limit on how much data can be loaded in a single chunk.  The real
> question is whether that limit is intentional or merely a bug.
> 
> Meanwhile, Brian Downing posted a patch to the pan bugreport:
> http://bugzilla.gnome.org/attachment.cgi?id=96917&action=view
> 
> His patch explicitly limits the amount of data Pan sends in one chunk,
> and this is the correct fix at least until we know if this size problem
> is a gdk bug or not.

I tried viewing an 8.5M jpeg using Dave's gtk+ patch
and it did not display correctly.  Also, I increased
JPEG_PROG_BUF_SIZE further to 1000000, but it still
didn't work right.  Then I tried Brian Downing's patch
on the SVN 324 version of pan2, and that worked fine for
the large jpeg.

I don't think this is going to surprise anyone, but I
thought you might like confirmation.

-- 
Greg