freetype.h: Improve Unicode Variation Sequence documentation.
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Werner Lemberg
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464b16ba46
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1c19b54999
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@ -3804,40 +3804,51 @@ FT_BEGIN_HEADER
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/* glyph_variants */
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/* */
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/* <Title> */
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/* Glyph Variants */
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/* Unicode Variation Sequences */
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/* */
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/* <Abstract> */
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/* The FreeType~2 interface to Unicode Ideographic Variation */
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/* Sequences (IVS), using the SFNT cmap format~14. */
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/* The FreeType~2 interface to Unicode Variation Sequences (UVS), */
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/* using the SFNT cmap format~14. */
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/* */
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/* <Description> */
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/* Many CJK characters have variant forms. They are a sort of grey */
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/* area somewhere between being totally irrelevant and semantically */
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/* distinct; for this reason, the Unicode consortium decided to */
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/* introduce Ideographic Variation Sequences (IVS), consisting of a */
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/* Unicode base character and one of 240 variant selectors */
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/* (U+E0100-U+E01EF), instead of further extending the already huge */
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/* code range for CJK characters. */
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/* Many characters, especially for CJK scripts, have variant forms. */
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/* They are a sort of grey area somewhere between being totally */
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/* irrelevant and semantically distinct; for this reason, the Unicode */
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/* consortium decided to introduce Variation Sequences (VS), */
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/* consisting of a Unicode base character and a variation selector */
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/* instead of further extending the already huge number of */
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/* characters. */
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/* */
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/* An IVS is registered and unique; for further details please refer */
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/* to Unicode Technical Standard #37, the Ideographic Variation */
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/* Database: */
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/* Unicode maintains two different sets, namely `Standardized */
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/* Variation Sequences' and registered `Ideographic Variation */
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/* Sequences' (IVS), collected in the `Ideographic Variation */
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/* Database' (IVD). */
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/* */
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/* http://www.unicode.org/reports/tr37/ */
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/* http://www.unicode.org/ivd/ */
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/* http://unicode.org/Public/UCD/latest/ucd/StandardizedVariants.txt */
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/* http://unicode.org/reports/tr37/ */
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/* http://unicode.org/ivd/ */
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/* */
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/* To date (January 2017), the character with the most variants is */
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/* U+9089, having 32 such IVS. */
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/* To date (January 2017), the character with the most ideographic */
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/* variations is U+9089, having 32 such IVS. */
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/* */
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/* Adobe and MS decided to support IVS with a new cmap subtable */
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/* (format~14). It is an odd subtable because it is not a mapping of */
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/* input code points to glyphs, but contains lists of all variants */
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/* supported by the font. */
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/* Three Mongolian Variation Selectors have the values U+180B-U+180D; */
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/* 256 generic Variation Selectors are encoded in the ranges */
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/* U+FE00-U+FE0F and U+E0100-U+E01EF. IVS currently use Variation */
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/* Selectors from the range U+E0100-U+E01EF only. */
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/* */
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/* A variant may be either `default' or `non-default'. A default */
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/* variant is the one you will get for that code point if you look it */
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/* up in the standard Unicode cmap. A non-default variant is a */
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/* different glyph. */
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/* A VS consists of the base character value followed by a single */
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/* Variation Selector. For example, to get the first variation of */
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/* U+9089, you have to write the character sequence `U+9089 U+E0100'. */
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/* */
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/* Adobe and MS decided to support both standardized and ideographic */
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/* VS with a new cmap subtable (format~14). It is an odd subtable */
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/* because it is not a mapping of input code points to glyphs, but */
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/* contains lists of all variations supported by the font. */
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/* */
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/* A variation may be either `default' or `non-default' for a given */
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/* font. A default variation is the one you will get for that code */
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/* point if you look it up in the standard Unicode cmap. A */
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/* non-default variation is a different glyph. */
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/* */
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/*************************************************************************/
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@ -3893,8 +3904,8 @@ FT_BEGIN_HEADER
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/* FT_Face_GetCharVariantIsDefault */
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/* */
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/* <Description> */
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/* Check whether this variant of this Unicode character is the one to */
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/* be found in the `cmap'. */
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/* Check whether this variation of this Unicode character is the one */
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/* to be found in the `cmap'. */
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/* */
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/* <Input> */
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/* face :: */
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@ -3908,7 +3919,7 @@ FT_BEGIN_HEADER
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/* */
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/* <Return> */
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/* 1~if found in the standard (Unicode) cmap, 0~if found in the */
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/* variation selector cmap, or -1 if it is not a variant. */
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/* variation selector cmap, or -1 if it is not a variation. */
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/* */
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/* <Note> */
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/* This function is only meaningful if the font has a variation */
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@ -3929,7 +3940,7 @@ FT_BEGIN_HEADER
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/* FT_Face_GetVariantSelectors */
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/* */
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/* <Description> */
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/* Return a zero-terminated list of Unicode variant selectors found */
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/* Return a zero-terminated list of Unicode variation selectors found */
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/* in the font. */
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/* */
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/* <Input> */
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@ -3938,7 +3949,7 @@ FT_BEGIN_HEADER
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/* */
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/* <Return> */
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/* A pointer to an array of selector code points, or NULL if there is */
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/* no valid variant selector cmap subtable. */
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/* no valid variation selector cmap subtable. */
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/* */
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/* <Note> */
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/* The last item in the array is~0; the array is owned by the */
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@ -3958,7 +3969,7 @@ FT_BEGIN_HEADER
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/* FT_Face_GetVariantsOfChar */
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/* */
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/* <Description> */
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/* Return a zero-terminated list of Unicode variant selectors found */
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/* Return a zero-terminated list of Unicode variation selectors found */
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/* for the specified character code. */
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/* */
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/* <Input> */
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@ -3969,7 +3980,7 @@ FT_BEGIN_HEADER
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/* The character codepoint in Unicode. */
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/* */
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/* <Return> */
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/* A pointer to an array of variant selector code points that are */
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/* A pointer to an array of variation selector code points that are */
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/* active for the given character, or NULL if the corresponding list */
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/* is empty. */
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/* */
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@ -3993,19 +4004,19 @@ FT_BEGIN_HEADER
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/* */
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/* <Description> */
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/* Return a zero-terminated list of Unicode character codes found for */
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/* the specified variant selector. */
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/* the specified variation selector. */
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/* */
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/* <Input> */
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/* face :: */
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/* A handle to the source face object. */
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/* */
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/* variantSelector :: */
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/* The variant selector code point in Unicode. */
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/* The variation selector code point in Unicode. */
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/* */
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/* <Return> */
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/* A list of all the code points that are specified by this selector */
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/* (both default and non-default codes are returned) or NULL if there */
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/* is no valid cmap or the variant selector is invalid. */
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/* is no valid cmap or the variation selector is invalid. */
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/* */
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/* <Note> */
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/* The last item in the array is~0; the array is owned by the */
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