 |
|
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Microsoft Typography | Developer information | Specifications | OpenType font development | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Kannada OpenType Specification | Terms | Shaping | Features | Other | Appendix | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
The features listed below have been defined to create the basic forms for the languages that are supported on Kannada systems. Regardless of the model an application chooses for supporting layout of complex scripts, Uniscribe requires a fixed order for executing features within a run of text to consistently obtain the proper basic form. This is achieved by calling features one-by-one in the standard order listed below. The order of the lookups within each feature is also very important. For more information on lookups and defining features in OpenType fonts, see Encoding feature information in the OpenType font development section. The standard order for applying Kannada features encoded in OpenType fonts:
Feature Tag: "akhn" This feature creates an akhand ligature glyph from two consonants in nominal forms separated by a halant: Cf + H + Cf -> Af The input context for the akhand feature always consists of the full form of the consonant. Examples of the Akhand feature applied:
Feature Tag: "rphf" Applying this feature produces the reph glyph: Ra + H -> Reph If the first consonant of the cluster consists of the (full form of Ra + Halant), this feature substitutes the combining-mark form of Reph. In addition, the glyph that represents the combining-mark form of Reph is repositioned in the glyph string: it is attached to the final base glyph of the consonant cluster. Reph feature applied:
Feature Tag: "blwf" Applying this feature produces below-base forms of consonants. Kf + H -> Ks The input context for the 'below-base form' feature must always consist of the full form of the consonant + Halant. The feature 'below-base form' is applied to consonants having below-base forms and following the base consonant. All characters encoded in Unicode v3.0 for Kannada, have a below base form. If a ligature is required between the vattu glyph and the preceding consonant, it will be handled by the feature 'Below base substitutions'. As a user types each character, the text-processing application will reshape the glyph or glyph cluster, which is displayed, as illustrated below. Example of the "blwf" feature applied.
Feature Tags: "abvs", "blws", "psts" All previous features have dealt with language features only, dedicated to forming glyph shapes dictated by the languages. The remaining shaping features cover optional features. These optional features range from those that will exist in every font to rare typographical ornaments. It is important to stress that all features operate only within one orthographic syllable. Since the language features do not limit typographical processing , Uniscribe passes the entire syllable to the OTL Services library. Uniscribe does not strictly specify the format of lookup tables to use or their inputs, allowing for context-dependent processing of any of the conjuncts and forms below. The OTL Services library processes the syllable "left to right", executing lookups in the order that they are specified in the font. First, pre-base substitutions will be handled, then below-base, above-base and then post-base substitutions. Therefore a font developer should first take care of all ligatures to the left of the base glyph and then working to the right, substite below-bases, above-bases and then finally post-base elements. The lookups in the font should be ordered in the same way. With every new element and feature, the following operations should be considered, as appropriate, in this order:
At every feature step, one should take into account all ligatures and forms that were produced by previous steps. In general, at this point the syllable being shaped will have one of the following forms:
Feature Tag: "abvs" Above-base Matra ligatures This feature produces the correct typographic shape when an above-base matra forms a ligature with the base glyph. It can also be used to contextually substitute the appropriate matra shape variant based on the consonant that it follows. The "abvs" feature applied:
This feature produces ligatures and forms involving above-base vowel modifiers as well as stress and tone marks. These marks can also be contextually substituted using this feauture.
Feature Tag: "blws" Below-base consonant conjuncts This feature produces conjuncts of the base glyph with below-base consonants. For example, Kf + {Ks} -> Lf Specific context-dependent forms or below-base consonants are handled by this lookup as well. Example 1:
Example 2:
Below-base Matra substitutions This feature produces matra ligatures with the base consonants. For example, Kf + Msub -> Ligature Lf + Msub -> Ligature Example of "blws" Matra ligature:
In the presence of below-base consonants, the below-base matra can be used for a ligature with them or change shape as well. Below-base Stress and Tone Marks This feature produces the correct form of signs like anudatta, depending on context.
Feature Tag: "psts" Post-base consonant conjuncts This feature produces ligatures of the base glyph with post-base forms of consonants. In Kannada, none of the consonants encoded in Unicode v3.0 have a post-base form. This feature can be used for the following instead.
This feature produces the correct typographic shape when a post-base matra forms a ligature with the base glyph.
Post-base vowel modifiers This feature produces different forms of post-base vowel modifiers, one among them is the visarga.
Feature Tag: "haln" This feature produces the halant form of the base glyph in syllables ending with a halant. Kf + H -> Khalant Lf + H -> Lhalant One can also realize halant forms by positioning the halant as a below-base mark on the base glyph. This feature is applied only on the base glyph and the following halant. "Halant Form of Consonant" feature applied.
Feature Tag: "abvm" This feature positions all above-base marks on the base glyph or the post-base matra. The best method for encoding this feature in an OpenType font is to use a chaining context positioning lookup that triggers mark-to-base and mark-to-mark attachments for below-base marks. "Above-base marks" feature applied (shaded box)
Feature Tag: "blwm" This feature positions all below-base marks on the base glyph. The best method for encoding this feature in an OpenType font is to use a chaining context positioning lookup that triggers mark-to-base and mark-to-mark attachments for below-base marks. The "Below-base marks" feature applied.
Feature Tag: "dist" This feature covers all other positioning lookups defining various distances between glyphs, such as kerning between pre- and post-base elements (like Visarga) and the base glyph.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Kannada OpenType Specification | Terms | Shaping | Features | Other | Appendix | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Microsoft Typography | Developer information | Specifications | OpenType font development | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
