Re: improvement of font selection

[Kenichi Handa <handa m17n org>]

In article <Pine LNX 4 58 0603150132040 9204 epoch cs>, Behdad Esfahbod <behdad cs toronto edu> writes:

>> Another reason for the change request is that we are now
>> developping a multilingual library m17n-lib
>> (http://www.m17n.org/m17n-lib), and it contains CTL (complex
>> text layout) rendering facility.  We can provide a pango
>> module using this library (single module can render many
>> scripts), but in that case also, the same problem happens.

> I know that library for a few years now, but never really looked
> into it in detail.  Any reason it has a separate CTL facility
> than Pango in the first place?

There are several reasons, but the biggest technical
difference with Pango is that it performs CTL not by
hard-coded program but by external database files which are
easily fixed/tuned/augmented.  Actually, even
non-C-programer can work on it.  For example, the attached
is for Arabic CTL.

---
Kenichi Handa
handa m17n org

;; ARAB-OTF.flt -- Font Layout Table for Arabic OpenType font
;; Copyright (C) 2004
;;   National Institute of Advanced Industrial Science and Technology (AIST)
;;   Registration Number H15PRO112

;; This file is part of the m17n database; a sub-part of the m17n
;; library.

;; The m17n library is free software; you can redistribute it and/or
;; modify it under the terms of the GNU Lesser General Public License
;; as published by the Free Software Foundation; either version 2.1 of
;; the License, or (at your option) any later version.

;; The m17n library is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
;; Lesser General Public License for more details.

;; You should have received a copy of the GNU Lesser General Public
;; License along with the m17n library; if not, write to the Free
;; Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
;; 02111-1307, USA.

;;; <li> ARAB-OTF.flt
;;;
;;; For Arabic OpenType fonts to draw the Arabic script.


;; Step 0: Move Kazakh high hamza.

(category
 ;; p: high hamza carrier (p for positive)
 ;; n: high hamza suppressor (n for negative)
 ;; x: don't care
 (0x0600 0x06FF		?x)
 (0x0674 0x0678		?p)
 (0x0643		?n)
 (0x06AF		?n)
 (0x06D5		?n)
 (0x200C		?x)
 (0x200D		?x)
 (0x25CC		?x)
 (0xFB50 0xFDFF		?X)		; Arabic Presentation Froms-A
 (0xFE70 0xFEFC		?X)		; Arabic Presentation Froms-B
 )

(generator
 (0
  (cond
   ;; If a presentation from is found, draw the whole sequence as is.
   (".*X.*" = *)

   (".*p.*"				; If a high hamza is found,
    (cond
     (".*n.*"				;   and a suppressor exists,
      rmhamza *)			;   then remove the high hamza.
     (0					;   Otherwise, move the high
      0x674 rmhamza *)))		;   hamza to the beginning.
   (0 = *)))				; If no high hamza, do nothing.

 (rmhamza
  (cond
   ((0x0674)		)
   ((0x0675)		0x0627)
   ((0x0676)		0x0648)
   ((0x0677)		0x06C7)
   ((0x0678)		0x0649)
   ("."			=))))

;; Step 1: ccmp

(category
 ;; D: Dual-joining (beh, teh, etc. & zwj)
 ;; R: Right-joining (alef, dal, thal, reh, zain)
 ;; U: Non-joining (Hamza, etc. & zwnj)
 ;; T: Transparent (combining marks)
 (0x060C 0x060F		?U)
 (0x0610 0x0615		?T)
 (0x061B		?U)
 (0x061F		?U)
 (0x0621		?U)
 (0x0622 0x0623		?R)
 (0x0624		?R)
 (0x0625		?R)
 (0x0626		?D)
 (0x0627		?R)
 (0x0628		?D)
 (0x0629		?R)
 (0x062A 0x062E		?D)
 (0x062F 0x0632		?R)
 (0x0633 0x0647		?D)
 (0x0648		?R)
 (0x0649 0x064A		?D)
 (0x064B 0x0658		?T)
 (0x0660 0x066D		?U)
 (0x066E 0x066F		?D)
 (0x0670		?T)
 (0x0671 0x0673		?R)
 (0x0674 0x0678		?U)
 (0x0679 0x0687		?D)
 (0x0688 0x0699		?R)
 (0x069A 0x06C3		?D)
 (0x06C4 0x06CB		?R)
 (0x06CC 0x06CE		?D)
 (0x06CF		?R)
 (0x06D0 0x06D3		?D)
 (0x06D4		?U)
 (0x06D5		?R)
 (0x06D6 0x06E4		?T)
 (0x06E5 0x06E6		?U)
 (0x06E7 0x06E8		?T)
 (0x06E9		?U)
 (0x06EA 0x06ED		?T)
 (0x06EE 0x06EF		?R)
 (0x06F0 0x06F9		?U)
 (0x06FA 0x06FC		?D)
 (0x06FD 0x06FE		?U)
 (0x06FF		?D)
 (0x200C		?U)
 (0x200D		?D)
 (0x25CC		?U)
 (0xFB50 0xFDFF		?X)		; Arabic Presentation Froms-A
 (0xFE70 0xFEFC		?X)		; Arabic Presentation Froms-B
 )

;; (generator
;;  (0
;;   otf:arab=ccmp))

;; Step 2: Initial, medial, or final.

(generator
 (0
  (cond
   (".*X.*" (cond ("[DRUX]T*" < = * >) ("." =)) *)

   ("D.*"
    (cond
     ("(.)(T*)([DR].*)"
      <
      (1 otf:arab=init)
      (2 = *)
      >
      (3 join))
     ("(.)(T*)(.*)"			; == (D)(T*)(U.*)
      <
      (1 otf:arab=isol)
      (2 = *)
      >
      (3 disjoin))))

   ("([RU])(T*)(.*)"
    <
    (1 otf:arab=isol)
    (2 = *)
    >
    (3 disjoin))

   ("(T+)(.*)"
    (1 = *)
    (2 disjoin))))

 (join
  (cond
   ("D.*"
    (cond
     ("(.)(T*)([DR].*)"
      <
      (1 otf:arab=medi)
      (2 = *)
      >
      (3 join))
     ("(.)(T*)(.*)"			; == (D)(T*)(U.*)
      <
      (1 otf:arab=fina)
      (2 = *)
      >
      (3 disjoin))))

   ("(.)(T*)(.*)"
    <
    (1 otf:arab=fina)
    (2 = *)
    >
    (3 disjoin))))

 (disjoin
  (cond
   ("D.*"
    (cond
     ("(.)(T*)([DR].*)"
      <
      (1 otf:arab=init)
      (2 = *)
      >
      (3 join))
     ("(.)(T*)(.*)"			; == (D)(T*)(U.*)
      <
      (1 otf:arab=isol)
      (2 = *)
      >
      (3 disjoin))))

   ("(.)(T*)(.*)"			; == ([RU])(T*)(.*)
    <
    (1 otf:arab=isol)
    (2 = *)
    >
    (3 disjoin)))))

;; Step 3: Other GSUB features (ligatures, etc.)

(generator
 (0
  otf:arab=rlig,calt,liga,dlig,cswh,mset))

;; Step 4: GPOS features.

(generator
 (0
  otf:arab=))

;; Local Variables:
;; mode: lisp
;; End: