User Guide

FontLab 4
68
Character and Glyph Identification
To simpl ify acc es s to th e c ha ra c te rs in the font ea ch c h ar ac ter h as an
identifier — an inte ge r numbe r or a tex t name. Al l font for ma ts a l l ow you to
q uick ly loca te a ch a ra cte r wh os e ide ntifier is k nown. A pr inting or
pre viewing pr og ra m tha t wants to output tex t c onver ts c h ar ac ter c od e s to
c ha ra cte r id e ntifie r s in th e font. Th is proc es s is us ua l ly pe rfor me d u sing a
s pe cial inde x t a b l e , c a l l e d t h e e n c o d i n g t a b le , which d e fine s the r e la tions hip
b et we en ch ar a cter c ode s and ide ntifie rs .
Note th a t th e ter m character cove rs all pos sibl e a ppe ar ance s of the
c ha r a cter in all fonts . All th es e “pictur e s” :
ar e th e
s ame ch a ra cte r ‘A ’ — the firs t lette r of th e E ng l is h a l p h a b e t . “ I n s t a n c e s ” o f
c ha ra cte rs th at h ave a u niq ue d e s i g n a r e c a l l e d glyphs. B ut note th at the
s ame pic tu re ‘A ’ m a y m e a n d i f f e r e n t c h a r a c t e r s – t h e f i r s t l e t t e r o f t h e
E ng lish al p h a b e t , t h e f i r s t l e t t e r o f t h e R u s s i a n a l p h a b e t a n d t h e f i r s t l e t t e r o f
the G re e k al pha be t can b e the s a me g l yph, b u t ar e not th e sa m e c h a r a c t e r .
Pre cise ch ar a cter id entific ation meth od s a r e r e a l ly nec e s s ar y.
The re is a d iffer enc e be twe en c h ar ac ter a nd gl yph ide ntifica tion. W h en we
nee d to id entify a cha ra c t e r i t m e a n s t h a t w e a r e i d e n t i f y i n g a l l g l y p h s t h a t
may b e use d to re pr e s e n t t h a t c h a r a c t e r . I f w e a r e i d e n t i f y i n g a g l y p h , i t i s
u niqu e.
Cha ra cte rs a r e id entifie d b y integ er nu mb er . To support ex ch a ng e of
infor ma tion this nu mbe r mus t be as sig ne d ac c or ding to s ome s tanda rd . I n
F ontL ab al l c h a r a c t e r s a r e i d e n t i f i e d a c c o r d i n g t o t h e U n i c o d e s t a n d a r d .
A g lyph is id entifie d by its na me or by its inde x – its se qu e ntia l numbe r in
the c ol l ec tion of g l yphs in the font. Since th e ind ex ma y va r y ( f o r i n s t a n c e , i f
we re move th e g lyph with inde x 5 th e ind ex es of a ll gl yph s th at ha v e l a r g e r
numbe rs , s ta r ting fr om 6 , wil l cha ng e ) it is not ve ry c onvenient, s o in mos t
c as es g l yphs a r e i d e n t i f ied b y names .
I t is ve ry important to und er sta nd th at the r e is no one -to-one re la tion
b et we en ch ar a cter s and g l yphs . It is poss ib l e t o h a v e s e v e r a l c h a r a c t e r s ( a n d
c ha ra cte r id e ntifie r s) r e fe r to a singl e na med g l yph. O n the othe r hand, some
g lyph s in th e font may not be c h ar ac ter s and may not ha ve a cha ra cte r
ide ntifier .