--- /dev/null
+;; BEN-OTF.flt -- Font Layout Table for Bengali 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> BEN-OTF.flt
+;;;
+;;; For Bengali OpenType fonts to draw Bengali script. Tested with
+;;; MuktiNarrow.ttf LikhanNormal.ttf. Both fonts are distributed by
+;;; the Free Bangla Fonts Project.
+;;; <http://www.nongnu.org/freebangfont/index.html>
+
+(category
+ ;; C: consonant (excluding B, Y and R)
+ ;; B: consonant BA (below)
+ ;; Y: consonant YA (post)
+ ;; R: consonant RA (reph, below)
+ ;; n: NUKTA
+ ;; H: HALANT
+ ;; m: MATRA (pre)
+ ;; b: MATRA (below)
+ ;; p: MATRA (post)
+ ;; o: MATRA (two-part O)
+ ;; u: MATRA (two-part AU)
+ ;; U: AU LENGTH MARK
+ ;; A: vowel modifier (above)
+ ;; a: vowel modifier (post)
+ ;; V: independent vowel
+ ;; N: ZWNJ (ZERO WIDTH NON-JOINER)
+ ;; J: ZWJ (ZERO WIDTH JOINER)
+ ;; E: ELSE
+ ;;
+ (0x200C ?N) ; ZWNJ
+ (0x200D ?J) ; ZWJ
+ (0x0964 0x0965 ?E) ; DANDA, DOUBLE DANDA
+ (0x0980 0x09FF ?E) ; ELSE
+ (0x0981 ?A) ; SIGN CANDRABINDU (above)
+ (0x0982 0x0983 ?a) ; SIGN ANUSWAR, VISARGA (post)
+ (0x0985 0x098C ?V) ; LETTER A .. VOCALIC L
+ (0x098F 0x0990 ?V) ; LETTER E .. AI
+ (0x0993 0x0994 ?V) ; LETTER O .. AU
+ (0x0995 0x09B9 ?C) ; LETTER KA .. HA
+ (0x09AC ?B) ; LETTER BA
+ (0x09AF ?Y) ; LETTER YA
+ (0x09B0 ?R) ; LETTER RA
+ (0x09BC ?n) ; SIGN NUKTA
+ (0x09BE ?p) ; VOWEL SIGN AA (post)
+ (0x09BF ?m) ; VOWEL SIGN I (pre)
+ (0x09C0 ?p) ; VOWEL SIGN II (post)
+ (0x09C1 0x09C4 ?b) ; VOWEL SIGN U, UU, R, RR (below)
+ (0x09C7 0x09C8 ?m) ; VOWEL SIGN E, AI (pre)
+ (0x09CB 0x09CC ?t) ; VOWEL SIGN O, AU (two-part)
+ (0x09CD ?H) ; SIGN VIRAMA (HASANT)
+ (0x09D7 ?p) ; AU LENGTH MARK
+ (0x09DC 0x09DD ?C) ; LETTER RRA, RHA
+ (0x09DF ?C) ; LETTER YYA
+ (0x09E0 0x09E1 ?V) ; LETTER VOCALIC RR, LL
+ (0x09E2 0x09E3 ?b) ; VOWEL SIGN L .. LL (below)
+ (0x09F1 0x09F2 ?C) ; LETTER RR', RR'' (assamese)
+ (0x09FE ?x) ; mark #1 (internal use)
+ (0x09FF ?y) ; mark #2 (internal use)
+ )
+
+;; Step 1 : Syllable identification. Recognised syllables are quoted
+;; by the virtual character, which is generated by the command "|" and
+;; has the category " " (space).
+(generator
+ (0
+ (cond
+ ;; Case A-C are for those syllables that end with an explicit vowel
+ ;; mark and/or a vowel modifier. They are divided into three cases
+ ;; for the readability of regular expression. The leading
+ ;; consonant-Hasant repetition is analysed for reordering in the
+ ;; next step. Two-part vowel, if any, is split for
+ ;; canonicalisation.
+
+ ;; Case A : A syllable ending with a vowel modifier.
+ ("(([CRBY]n?H[NJ]?)*([CRBY]n?))([mbp]*)(t)?([Aa])"
+ < |
+ (1 set-marks)
+ (4 = *)
+ (5 split)
+ (6 =)
+ | >)
+
+ ;; Case B : A syllable ending with a two-part vowel.
+ ("(([CRBY]n?H[NJ]?)*([CRBY]n?))(t)"
+ < |
+ (1 set-marks)
+ (4 split)
+ | >)
+
+ ;; Case C : A syllable ending with other vowel. Note that a
+ ;; two-part vowel may be expressed with two vowel marks for
+ ;; backward compatibility.
+ ("(([CRBY]n?H[NJ]?)*([CRBY]n?))([mbp]+)"
+ < |
+ (1 set-marks)
+ (4 = *)
+ | >)
+
+ ;; Case D : Ya-phalaa. Reorder H and Y for the next step.
+ ;; The web page "Unicode FAQ for Indic Scripts and Languages"
+ ;; <http://www.unicode.org/faq/indic.html> says "it should be
+ ;; permissible for the Ya-phalla to be consistently formed by "ZWNJ
+ ;; + VIRAMA + YA".
+ ("([CBRY]N)(H)(Y)"
+ < |
+ (1 = =)
+ (3 =)
+ (2 =)
+ | >)
+
+ ;; Case E : No explicit vowel nor modifier. If the syllable ends
+ ;; with a consonant, analyse it for reordering in the next step.
+ ;; Otherwise, just identify the syllable without changing anything.
+ ("([CRBY]n?H[NJ]?)*[CRBY]n?(HN|HJ|H)?"
+ (cond
+ (".+[^HNJ]$"
+ < | set-marks | >)
+ (".+"
+ < | = * | >)))
+
+ ;; Case F : Syllables that begin with an independent vowel. An
+ ;; optional HYp sequence appears when this syllable represents the
+ ;; sound "a" in English "bat" (see the FAQ above). If it appears,
+ ;; we reorder the H and Y for the next step.
+ ("(V)(HYp)?([aA])?"
+ < | (1 =) (2 ("HY(p)" 0x09AF 0x09CD (1 =))) (3 =) | >)
+
+ ("." =))
+ *)
+
+ ;; Set mark #1 (x) at the position where below consonants begin, and
+ ;; mark #2 (y) at the position to which below and above signs will be
+ ;; moved.
+ (set-marks
+ (cond
+ ;; At least one C and ends with Y.
+ ("(([CRBY]n?H[NJ]?)*Cn?)H(([BR]H)*)Y"
+ (1 = *)
+ 0x09FE ; mark #1
+ (3 = *) ; below consonants
+ 0x09FF ; mark #2
+ 0x09AF 0x09CD) ; YA + moved HASANT
+ ;; At least one C and ends with B or R.
+ ("(([CRBY]n?H[NJ]?)*Cn?)H(([BR]H)*[BR])"
+ (1 = *)
+ 0x09FE ; mark #1
+ (3 = *) ; below consonants
+ 0x09CD ; moved HASANT
+ 0x09FF) ; mark #2
+ (".+"
+ = *
+ 0x09FE ; mark #1
+ 0x09FF))) ; mark #2
+
+ ;; Split two-part dependent vowel signs for canonicalisation.
+ (split
+ (cond
+ ((0x09CB) 0x09C7 0x09BE)
+ ((0x09CC) 0x09C7 0x09D7)))
+ )
+
+;; Step 2 : Move Reph and Matra if necessary. From now on, we care
+;; for only those syllables that were identified in Step 1.
+(generator
+ (0
+ (cond
+ ;; This is the most generic pattern. It follows Case A-C and a
+ ;; part of Case E in Step 1. Now Mark #1 is used to indicate the
+ ;; critical part that require pre-base substitution in the
+ ;; following steps.
+
+ ;; 1 2 3 4 5 6 7 8 9
+ (" (RH)?([^ xy]+)x([^ y]*)y(YH)?(m)?(b)?(p)?(A)?(a)? "
+ |
+ (5 =) ; [Mpre]
+ 0x09FE
+ ;; Actually, the nukt feature is not necessary for Bengali because
+ ;; all the necessary Nukta forms are precomposed in the Unicode
+ ;; standard. Even if a Nukta consonant is given in the form of
+ ;; the combination of the base consonant and a Nukta sign, we can
+ ;; safely perm the composition here because it does not affect
+ ;; surrounding letters in the syllable. The Akhand ligature
+ ;; operation is also applied here, before applying the half form
+ ;; operation because the Mukti font generates Akhand ligatures
+ ;; directly from the "C H C" sequence, not via the half form.
+ (2 otf:beng=nukt,akhn) ; {Cpre + H} + Cbase
+ 0x09FE
+ (3 otf:beng=blwf) ; {Cbelow + H}
+ (6 =) ; [Mbelow]
+ (1 otf:beng=rphf) ; [Reph]
+ (8 =) ; [VMabove]
+ (4 otf:beng=pstf) ; [Cpost + H]
+ (7 =) ; [Mpost]
+ (9 =) ; [VMpost]
+ |)
+
+ ;; Syllables that begin with an independent vowel (following up
+ ;; Step 1, Case F). If a YH sequence exist, it is changed to the
+ ;; post base form. This type of syllables do not require further
+ ;; modification.
+ (" (V)(YH)(.*) "
+ |
+ (1 =)
+ (2 otf:beng=pstf)
+ (3 = *)
+ |)
+
+ ;; Ya-phalaa (following up Step 1, Case D). Remove N and change YH
+ ;; to the post base form. This type of syllables do not require
+ ;; further modification.
+ (" ([CBRY])N(YH) "
+ |
+ (1 =)
+ (2 otf:beng=pstf)
+ |)
+
+ ;; Syllables that end with H and an optional N or J (following up a
+ ;; part of Step 1, Case E). This type of syllables also require
+ ;; pre-base substitution in the following steps.
+ (" ([^ ]+H[NJ]?) "
+ |
+ 0x09FE
+ ;; Only Nukt and Akhn are applied here. See the comment in the
+ ;; topmost sibling for explanation.
+ (1 otf:beng=nukt,akhn)
+ 0x09FE
+ |)
+
+ ("." =))
+ *))
+
+;; Step 3 : Now only those syllables that contain the virtual
+;; character x require pre-base substition. This is the most
+;; complicated part in this FLT.
+
+;; If the sequence "C1 H C2" makes ligature L12, L12 replaces the
+;; original sequence.
+
+;; To test the availability of such a ligature, we try to generate it
+;; using the pre-base substitute feature, then see whether succeeded
+;; or not. In the case of failure, the pre-base feature does not
+;; change the original sequence.
+
+;; To create a ligature, the "C1 H" part must be first converted into
+;; the half form of C1. Creating the half form of a consonant always
+;; succeeds.
+
+;; ligature(half(C1,H),C2)
+;; ==> ligature(C1half,C2)
+;; ==> L12 ; success
+;; C1half C2 ; fail
+
+;; If the ligature is not available, the "C1 H" part must be converted
+;; into the _Halant_ (not half) form of C1. However, there is no way
+;; to reconvert C1half into C1halant nor to revert back to "C1 H".
+;; Thus we duplicate the critical part in two different forms so that
+;; we can select the appropriate one in the next step. The virtual
+;; character x is used to indicate the boundaries.
+
+;; ... C1 H C2 ... ==> ... x C1halant C2 x L12 x ...
+
+;; If the length of the L12 part is one, ligature generation was
+;; successful. In this case we wipe out the duplicated C1halant and
+;; C2. Otherwise we remove L12.
+
+;; In very few cases (I found only one in the Mukti font), the "C1 H"
+;; part need to be converted into C1halant to make a ligature with C2.
+;; So when try to generate a ligature form, we apply the GSUB features
+;; "half", "haln" and "pres" in this order.
+
+(category
+ ;; C: consonant (excluding B, Y and R)
+ ;; H: HALANT
+ ;; N: ZWNJ (ZERO WIDTH NON-JOINER)
+ ;; J: ZWJ (ZERO WIDTH JOINER)
+ ;; E: ELSE
+ ;;
+ (0x200C ?N) ; ZWNJ
+ (0x200D ?J) ; ZWJ
+ (0x0964 0x0965 ?E) ; DANDA, DOUBLE DANDA
+ (0x0980 0x09FF ?E) ; ELSE
+ (0x09CD ?H) ; SIGN VIRAMA (HASANT)
+ (0x0995 ?K) ; LETTER KA
+ (0x09B7 ?S) ; LETTER SSA
+ (0x09A8 ?M) ; LETTER NA
+ (0x09AE ?M) ; LETTER MA
+ (0x09FE ?x) ; mark #1 (internal use)
+ )
+
+(generator
+ (0
+ (cond
+
+ ;; One pre-base and base.
+ ;; 1 23 4 5 6
+ (" ([^x ]*)x((.H)([^NJ]))(H)?x([^ ]*) "
+ |
+ (1 = *)
+ 0x09FE ; x
+ (3 otf:beng=haln) ; C1halant
+ (4 =) ; C2
+ 0x09FE ; x
+ (2 otf:beng=half,haln,pres) ; ligature result
+ 0x09FE ; x
+ (5 =)
+ (6 = *)
+ |)
+
+ ;; One pre-base with ZWJ. According to the Unicode FAQ, the half
+ ;; form is forced in this case. So we fake as if ligature
+ ;; generation was failed.
+ (" ([^x ]*)x(.H)J(.)?x([^ ]*) "
+ |
+ (1 = *)
+ 0x09FE ; x
+ (2 otf:beng=half) ; C1half
+ (3 =) ; C2
+ 0x09FE ; x
+ 0x09FD ; pseudo result
+ 0x09FD ; pseudo result
+ 0x09FE ; x
+ (4 = *)
+ |)
+
+ ;; One pre-base possibly with ZWNJ. Similar to above.
+ (" ([^x ]*)x(.H)N?(.)?x([^ ]*) "
+ |
+ (1 = *)
+ 0x09FE ; x
+ (2 otf:beng=haln) ; C1halant
+ (3 =) ; C2
+ 0x09FE ; x
+ 0x09FD ; pseudo result
+ 0x09FD ; pseudo result
+ 0x09FE ; x
+ (4 = *)
+ |)
+
+ ;; Standalone base. There is nothing more to do.
+ (" ([^x ]*)x(.)x([^ ]*) "
+ |
+ (1 = *)
+ (2 =)
+ (3 = *)
+ |)
+
+ ;; KA-SSA-NA and KA-SSA-MA are the only pre-base ligatures that
+ ;; consist of three consonants.
+ ;; 1 23 4 5 6 7
+ (" ([^x ]*)x((KH)(SH)(M))(H)?x([^ ]*) "
+ |
+ (1 = *)
+ 0x09FE ; x
+ (3 otf:beng=haln) ; KAhalant
+ (4 otf:beng=haln) ; SSAhalant
+ (5 =) ; NA or MA
+ 0x09FE ; x
+ (2 otf:beng=half,haln,pres) ; ligature result
+ 0x09FE ; x
+ (6 =)
+ (7 = *)
+ |)
+
+ ;; Two or more pre-bases plus base. Give up. Convert all
+ ;; pre-bases into halant form.
+ ;; 1 23 4 5
+ (" ([^x ]*)x(([^x]H[JN]?)+)([^x])?x([^ ]*) "
+ |
+ (1 = *)
+ 0x09FE ; x
+ (2 force-haln) ; halant forms
+ (4 =) ; full form
+ 0x09FE ; x
+ 0x09FD ; pseudo result
+ 0x09FD ; pseudo result
+ 0x09FE ; x
+ (5 = *)
+ |)
+
+ ("." =))
+ *)
+
+ ;; This is to remove ZWNJ and ZWJ. The half-form-force-effect of ZWJ
+ ;; is ignored. Sorry.
+ (force-haln
+ (cond
+ ("([^JN]*)[JN](.*)"
+ (1 otf:beng=haln)
+ (2 force-haln))
+ (".+"
+ otf:beng=haln)))
+ )
+
+;; Step 4 : Select the appropriate representation. Only those
+;; syllables that contain the virtual character x require
+;; modification.
+(generator
+ (0
+ (cond
+ ;; Only one glyph in the ligature section (between the second and
+ ;; the third x). It means a ligature was successfully generated.
+ ;; C1halant and C2 (between the first and second x) are removed.
+ (" ([^x ]*)x[^x]+x(.)x([^ ]*) "
+ |
+ (1 = *)
+ (2 =)
+ (3 = *)
+ |)
+
+ ;; Otherwise halant and base forms are used. The failed ligature
+ ;; is removed.
+ (" ([^x ]*)x([^x]+)x[^x]+x([^ ]*) "
+ |
+ (1 = *)
+ (2 = *)
+ (3 = *)
+ |)
+
+ ;; No need to care the other cases.
+ ("." =))
+ *))
+
+;; Step 5 : Fine adjustments. Select appropriate glyph variants and
+;; apply GPOS features. Now the syllable boundary marks are removed
+;; so that the final step can find word boundaries.
+(generator
+ (0
+ (cond
+ (" ([^ ]+) "
+ (1 otf:beng=blws,abvs,psts,vatu))
+ ("."
+ [ otf:beng=+ ] ))
+ *)
+ )
+
+;; Step 6 : Word initial substitute. As the syllable boundaries has
+;; been eliminated in the previous step, this rule is applied to a run
+;; of Bengali glyphs, i.e. word by word. We finally apply the init
+;; feature to the word initial gylphs and everything is over.
+(generator
+ (0
+ ("(.)(.*)"
+ (1 otf:beng=init)
+ (2 = *))))
+
+;; Local Variables:
+;; mode: emacs-lisp
+;; End:
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