[Koha-bugs] [Bug 14107] Patron cards: Make barcode width and height scaling editable

[bugzilla-daemon at bugs.koha-community.org]

http://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=14107

--- Comment #14 from Heinrich Hartl <Heinrich.Hartl at email.de> ---
I have done a little bit black box analysis: how does the bar code behave under
different sized labels/cards. The analysis is done with 3.18.5, hence without
this patch or any other modification.

1. The bar code position defines the position of the lower left corner of the
bar code string (as designed). The bar code includes a little bit of white lead
space, approximately half a code character.Therefore the first black bar of the
bar code is found that amount to the right of the defined start position.
2.The length of the bar code string including white lead and trailing space is
approximately 75% of the label width. if this observed length is associated
with a value 0.8 some extra space is included in the calculation. 
3. The lower left position defined is the baseline of the human readable
string. If that string is not printed the height reserved for the human
readable string is left blank.
4. the height of human readable string + the bar code is about 27% of the
label/card height. The bar code alone is 20% of the label/card height. If these
values are associated with an internal scale 0.01 I do not know to which basis
this scale is chosen. 14 digits + start char + stop char were measured 49 mm
long 7mm high on a template with label/cards 70*36mm close to credit card size
85*54mm. Aspect ratio of bar code letters h/w hence was 7/3 w~0.5*h.

Unfortunately the bar code is the only element of the layout that reacts to the
size of the label/card. All text and pictures remain same size and position
(with respect to lower left corner) with disregard to the size of the
label/card
I think it is desirable to have a consistent and foreseeable behaviour.

May I suggest to think about giving the barcode a height in chosen units and
define its (estimated) length from the number of characters in string *
character width (derived from height * aspect factor 0,5). It is then the users
responsibility to choose a barcode height in the layout which results an
acceptable string length not exceeding the available space on the label/card.

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