Problem with libpng on mac OSX.6

[Arnaud BOEGLIN]

> Hi,
>
> I work on a project which uses libpng. I always worked with the  
> version
> 1.2.39. I recently installed mac OS X.6. So I recompiled libpng, I  
> modified
> my project's configuration, but I've got an error while loading the  
> png
> file. The function which crashes is : png_get_IHDR. The output is :  
> "libpng
> error: Invalid image width".
>
> I tried with a lot of different images, it's the same for all.
>
> If you came light me ..
>
> Regards,
> Arnaud BOEGLIN.

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[John Bowler-3]

From: Arnaud BOEGLIN [mailto:a.boeglin67@...]
>The function which crashes is : png_get_IHDR. The output is :  
> "libpng error: Invalid image width".

I think that means 'width' is 0, because the other case (width > 0x7fffffff)
has already been excluded.

There are two possibilities, one, by far the most likely, is that something
in your code is overwriting the "info_ptr" memory to zero out the width
field, or maybe much of the structure (but not bit_depth).  Zeroing most
fields will produce values that pass the initial checks in png_get_IDHR but
fail at 'width'.

Look at the value of width in a debugger (or add a printf to libpng) - is it
0?  If not, what is it (and how did it get that way ;-)  If it is zero take
a look at the other fields, like color_type - is that 0 too.  Should it be?
(Try with an image where it shouldn't be zero.)

The second possibility, really unlikely, is that you have compiled with
PNG_READ_BIG_ENDIAN_SUPPORTED on a platform that doesn't support it and this
has resulted in the info_ptr->width field ending up '0' even though the
bytes in the header didn't say 0.

This will happen if you set that option on a big-endian ARM system (for
example) where the unaligned data access exception handling has been
switched off (the default, IRC.)

BTW, "PNG_READ_BIG_ENDIAN_SUPPORTED" should *never* be switched on for ARM -
ARM support for unaligned data access is *much* slower than the byte-by-byte
code in libpng.

John Bowler <jbowler@...>



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[Glenn Randers-Pehrson]

On Wed, Sep 23, 2009 at 7:39 PM, Arnaud BOEGLIN <a.boeglin67@...> wrote:

>> Hi,
>>
>> I work on a project which uses libpng. I always worked with the
>> version
>> 1.2.39. I recently installed mac OS X.6. So I recompiled libpng, I
>> modified
>> my project's configuration, but I've got an error while loading the
>> png
>> file. The function which crashes is : png_get_IHDR. The output is :
>> "libpng
>> error: Invalid image width".
>>
>> I tried with a lot of different images, it's the same for all.

Please try building your application with libpng-1.4.0beta82 and
see if the error reporting is more useful.

Glenn

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