The Khmer Script Tamed by the Lion ( of TEX )

This paper presents a Khmer typesetting system, based on TEX, METAFONT, and an ANSI-C filter. A 128-character of the -/-bit ASCII table for the Khmer script is proposed. Input of text is done phonically (using the spoken order consonantsubscript consonant-second subscript consonant-vowel-diacritic). The filter converts phonic description of consonantal clusters into a graphc T~Xnical description of these. Thanks to TEX booleans, independent vowels can be automatically decomposed accordmg to recent reforms of Khmer spelling. The last section presents a forthcoming implementation of Khmer into a 16-bit TEX output font, solving the kerning problem of consonantal clusters. Introduction to Khmer Script The Khmer script is used to write Khmer, the official language of the Cambodian Republic, and belongs to the Mon-Khmer group of Austroasiatic languages. It is a very old and beautiful script, and from the typesetter's point of view, one of the most challenging and exciting scripts in the world. To understand the complications of Khmer typesetting, we will start with a quick overview of the Khmer writing system. Khmer is written from left to right; the Khmer alphabet has 32 consonants, the following: f i Z ~ Z ~ ' L 7 ~ ~ ~ b T ~ ~ 4 6 ~ 6 1 $ 1 % i I ? 1 ~ ~ 6 ~ ' 6 6 1 ' 6 ~ ~ h ; d 6 ~ i $ ~ U l ~ The character H denotes the absence of a consonant. From the typesetter's point of view and with respect to collating order, it might as well be considered as a consonant. We wdl use a box U to denote an arbitrary consonant. These 33 "consonants" (except 4) can appear in the form of subscript consonants: LO 0 0 OJ 0 0 oi d cr H A subscript consonant is pronounced after the "primary" consonant. Nevertheless, as the reader has certalnly noticed, the subscript consonant I3 is written on the left of the primary consonant. It is also possible to have two subscript consonants carried by the same primary consonant. In that case, the second subscript consonant has to be LO. Examples: k, N. Ln I. A consonant, consonant + subscript or consonant + double subscript combination can carry a vowel. There are 28 vowels: Although vowels are always pronounced after consonants, their graphical representation literally surrounds the consonant/subscript combination: they can appear above, beneath, on the right or on the left of consonants. Often a vowel's glyph has two or three non-connected parts. When combining vowels with subscript consonants, the following graphical rules are followed: if the subscript has a right protrudmg stem then the vowel 01 connects to the subscript and not to the consonant: GJ + G? = 9 etc. if the consonant carries both a subscript LU and a vowel with left branch, then the latter is placed on the left of the former: LG + 60 = 610 etc. if the consonant carries both a subscript consonant and a subscript vowel, then the latter is placed underneath the former: + Q = i, 10+ g = IG etc.