Re: [Libexif-devel] Need some help with adding support for extra canon makernotes

[Jan P. <pa...@pi...>]

Jef,

I inspected
http://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/Canon.html#FocalLength
and here is what I have found out:
1) MNOTE_CANON_TAG_FOCAL_LENGTH data is expected to be of the
EXIF_FORMAT_SHORT format and to have 4 items
2) the 1st value is FocalType, and not size of any kind.

Thus the correct sanity checks & code are:
   CF (entry->format, EXIF_FORMAT_SHORT, val, maxlen);
   CC (entry->components, 4, val, maxlen);
   if (t >= 4) return NULL;
   vs = exif_get_short (entry->data + t * 2, entry->order);

Kind regards,
           Jan Patera

> Marcus Meissner wrote:
>> On Wed, Sep 06, 2006 at 03:39:30PM +0200, Jef Driesen wrote:
>>> Jan Patera wrote:
>>>>> case MNOTE_CANON_TAG_FOCAL_LENGTH:
>>>>>     CF (entry->format, EXIF_FORMAT_SHORT, val, maxlen);
>>>>>     n = exif_get_short (data, entry->order) / 2;
>>>>>     if (t >= n) return NULL;
>>>>>     CC (entry->components, n, val, maxlen);
>>>>>     vs = exif_get_short (entry->data + 2 + t * 2, entry->order);
>>>>> snprintf (buf, sizeof (buf), "0x%04x", vs);
>>>>>     strncpy (val, buf, maxlen - strlen (val));
>>>>>     break;
>>>>>
>>>>> But when I run the exif commandline utility, an error is reported
>>>>> for the new tag:
>>>>>
>>>>> Focal type          |Invalid number of components (4, expected 1).
>>>>>
>>>>> What am I doing wrong here?
>>>>
>>>> this message is printed by the CC macro. It checks whether
>>>> 1st & 2nd arguments are equal. apparently entry->components is 4,
>>>> but n is only 1.
>>> I knew it was reported by the CC macro, but I don't understand why it
>>> is happening. It is exactly the same code as is used for
>>> MNOTE_CANON_TAG_SETTINGS_1 (which also has multiple components), but
>>> no error there! Probably I forgot to add some code somewhere else,
>>> but I don't see it.
>>
>> Just a wild guess:
>> Did you adjust mnote_canon_entry_count_values() too?
>
> I added an extra 'case MNOTE_CANON_TAG_FOCAL_LENGTH:' between the
> others.