The software offers support for OpenType GPOS tables when used with TTOpen. This allows for greater flexibility and precision in font design, allowing designers to create more advanced text layouts.
Font::TTF::GPOS is a Perl module that provides support for Opentype GPOS tables in conjunction with TTOpen. The GPOS table is one of the most complicated tables in the TTF spec and the corresponding data structure abstraction is also not trivial.
Much of the structure of a GPOS is shared with a GSUB table via the Font::TTF::Ttopen INSTANCE VARIABLES. Here we describe the additions and lookup specific information for GPOS tables. Unfortunately, there is no one abstraction that seems to work comfortably for all GPOS tables, so we will also examine how the variables are used for different lookup types.
The following are the values allowed in the ACTION_TYPE and MATCH_TYPE variables:
ACTION_TYPE:
- "a": The ACTION is an array of anchor tables
- "o": Offset. There is no RULE array. The ADJUST variable contains a value record.
- "v": The ACTION is a value record.
- "p": Pair adjustment. The ACTION contains an array of two value records for the matched two glyphs.
- "e": Exit and entry records. The ACTION contains an array of two anchors corresponding to the exit and entry anchors for the glyph.
- "l": Indicates a lookup based contextual rule as per the GSUB table.
MATCH_TYPE:
- "g": A glyph array
- "c": An array of class values
- "o": An array of coverage tables.
Overall, Font::TTF::GPOS provides a comprehensive solution for those looking to work with Opentype GPOS tables. Its support for a wide range of values in the ACTION_TYPE and MATCH_TYPE variables makes it a robust and versatile tool for developers.
Much of the structure of a GPOS is shared with a GSUB table via the Font::TTF::Ttopen INSTANCE VARIABLES. Here we describe the additions and lookup specific information for GPOS tables. Unfortunately, there is no one abstraction that seems to work comfortably for all GPOS tables, so we will also examine how the variables are used for different lookup types.
The following are the values allowed in the ACTION_TYPE and MATCH_TYPE variables:
ACTION_TYPE:
- "a": The ACTION is an array of anchor tables
- "o": Offset. There is no RULE array. The ADJUST variable contains a value record.
- "v": The ACTION is a value record.
- "p": Pair adjustment. The ACTION contains an array of two value records for the matched two glyphs.
- "e": Exit and entry records. The ACTION contains an array of two anchors corresponding to the exit and entry anchors for the glyph.
- "l": Indicates a lookup based contextual rule as per the GSUB table.
MATCH_TYPE:
- "g": A glyph array
- "c": An array of class values
- "o": An array of coverage tables.
Overall, Font::TTF::GPOS provides a comprehensive solution for those looking to work with Opentype GPOS tables. Its support for a wide range of values in the ACTION_TYPE and MATCH_TYPE variables makes it a robust and versatile tool for developers.
What's New
Version 0.45: N/A