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@ -22,7 +22,7 @@ |
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correct amount for each successive glyph. |
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</para> |
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<para> |
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But, for <emphasis>complex scripts</emphasis>, any combination of |
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But, for other scripts (often unceremoniously called <emphasis>complex scripts</emphasis>), any combination of |
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several shaping operations may be required, and the rules for how |
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and when they are applied vary from script to script. HarfBuzz and |
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other shaping engines implement these rules. |
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@ -36,42 +36,35 @@ |
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</para> |
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</section> |
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<section id="complex-scripts"> |
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<title>Complex scripts</title> |
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<section id="script-specific-shaping"> |
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<title>Script-specific shaping</title> |
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<para> |
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In text-shaping terminology, scripts are generally classified as |
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either <emphasis>complex</emphasis> or <emphasis>non-complex</emphasis>. |
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</para> |
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<para> |
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Complex scripts are those for which transforming the input |
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sequence into the final layout requires some combination of |
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In many scripts, transforming the input |
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sequence into the final layout often requires some combination of |
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operations—such as context-dependent substitutions, |
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context-dependent mark positioning, glyph-to-glyph joining, |
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glyph reordering, or glyph stacking. |
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</para> |
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<para> |
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In some complex scripts, the shaping rules require that a text |
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In some scripts, the shaping rules require that a text |
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run be divided into syllables before the operations can be |
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applied. Other complex scripts may apply shaping operations over |
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applied. Other scripts may apply shaping operations over |
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entire words or over the entire text run, with no subdivision |
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required. |
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</para> |
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<para> |
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Non-complex scripts, by definition, do not require these |
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operations. However, correctly shaping a text run in a |
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non-complex script may still involve Unicode normalization, |
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Other scripts, do not require these |
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operations. However, correctly shaping a text run in |
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any script may still involve Unicode normalization, |
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ligature substitutions, mark positioning, kerning, and applying |
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other font features. The key difference is that a text run in a |
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non-complex script can be processed sequentially and in the same |
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order as the input sequence of Unicode codepoints, without |
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requiring an analysis stage. |
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other font features. |
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</para> |
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</section> |
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<section id="shaping-operations"> |
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<title>Shaping operations</title> |
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<para> |
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Shaping a complex-script text run involves transforming the |
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Shaping a text run involves transforming the |
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input sequence of Unicode codepoints with some combination of |
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operations that is specified in the shaping model for the |
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script. |
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@ -81,7 +74,7 @@ |
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text run varies from script to script, as do the order that the |
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operations are performed in and which codepoints are |
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affected. However, the same general set of shaping operations is |
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common to all of the complex-script shaping models. |
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common to all of the script shaping models. |
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</para> |
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<itemizedlist> |
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@ -92,7 +85,7 @@ |
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some other ("visual") position. |
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</para> |
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<para> |
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The shaping model for a given complex script might involve |
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The shaping model for a given script might involve |
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more than one reordering step. |
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</para> |
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</listitem> |
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@ -119,7 +112,7 @@ |
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particular string pattern. |
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</para> |
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<para> |
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The shaping model for a given complex script might involve |
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The shaping model for a given script might involve |
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multiple contextual-substitution operations, each applying |
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to different target glyphs and patterns, and which are |
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performed in separate steps. |
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@ -138,7 +131,7 @@ |
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Many contextual positioning operations are used to place |
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<emphasis>mark</emphasis> glyphs (such as diacritics, vowel |
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signs, and tone markers) with respect to |
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<emphasis>base</emphasis> glyphs. However, some complex |
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<emphasis>base</emphasis> glyphs. However, some |
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scripts may use contextual positioning operations to |
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correctly place base glyphs as well, such as |
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when the script uses <emphasis>stacking</emphasis> characters. |
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@ -194,7 +187,7 @@ |
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multiple positions). |
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</para> |
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<para> |
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Some complex scripts require that the text run be split into |
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Some scripts require that the text run be split into |
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syllables. What constitutes a valid syllable in these |
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scripts is specified in regular expressions, formed from the |
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Letter and Mark codepoints, that take the UISC and UIPC |
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@ -235,7 +228,7 @@ |
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<listitem> |
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<para> |
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The <emphasis>default</emphasis> shaping model handles all |
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non-complex scripts, and may also be used as a fallback for |
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scripts with no script-specific shaping model, and may also be used as a fallback for |
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handling unrecognized scripts. |
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</para> |
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</listitem> |
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@ -310,7 +303,7 @@ |
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<listitem> |
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<para> |
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The <emphasis>Universal Shaping Engine</emphasis> (USE) |
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shaping model supports complex scripts not covered by one of |
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shaping model supports scripts not covered by one of |
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the above, script-specific shaping models, including |
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Javanese, Balinese, Buginese, Batak, Chakma, Lepcha, Modi, |
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Phags-pa, Tagalog, Siddham, Sundanese, Tai Le, Tai Tham, Tai |
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Khaled Hosny
3 years ago
committed by
Behdad Esfahbod