read_fonts/tables/
gsub.rs

1//! the [GSUB] table
2//!
3//! [GSUB]: https://docs.microsoft.com/en-us/typography/opentype/spec/gsub
4
5pub use super::layout::{
6    ChainedSequenceContext, ClassDef, CoverageTable, Device, FeatureList, FeatureVariations,
7    Lookup, LookupList, ScriptList, SequenceContext,
8};
9use super::layout::{ExtensionLookup, LookupFlag, Subtables};
10
11#[cfg(feature = "std")]
12mod closure;
13#[cfg(test)]
14#[path = "../tests/test_gsub.rs"]
15mod tests;
16
17include!("../../generated/generated_gsub.rs");
18
19/// A typed GSUB [LookupList] table
20pub type SubstitutionLookupList<'a> = LookupList<'a, SubstitutionLookup<'a>>;
21
22/// A GSUB [SequenceContext]
23pub type SubstitutionSequenceContext<'a> = super::layout::SequenceContext<'a>;
24
25/// A GSUB [ChainedSequenceContext]
26pub type SubstitutionChainContext<'a> = super::layout::ChainedSequenceContext<'a>;
27
28impl<'a, T: FontRead<'a>> ExtensionLookup<'a, T> for ExtensionSubstFormat1<'a, T> {
29    fn extension(&self) -> Result<T, ReadError> {
30        self.extension()
31    }
32}
33
34type SubSubtables<'a, T> = Subtables<'a, T, ExtensionSubstFormat1<'a, T>>;
35
36/// The subtables from a GPOS lookup.
37///
38/// This type is a convenience that removes the need to dig into the
39/// [`SubstitutionLookup`] enum in order to access subtables, and it also abstracts
40/// away the distinction between extension and non-extension lookups.
41pub enum SubstitutionSubtables<'a> {
42    Single(SubSubtables<'a, SingleSubst<'a>>),
43    Multiple(SubSubtables<'a, MultipleSubstFormat1<'a>>),
44    Alternate(SubSubtables<'a, AlternateSubstFormat1<'a>>),
45    Ligature(SubSubtables<'a, LigatureSubstFormat1<'a>>),
46    Contextual(SubSubtables<'a, SubstitutionSequenceContext<'a>>),
47    ChainContextual(SubSubtables<'a, SubstitutionChainContext<'a>>),
48    Reverse(SubSubtables<'a, ReverseChainSingleSubstFormat1<'a>>),
49}
50
51impl<'a> SubstitutionLookup<'a> {
52    pub fn lookup_flag(&self) -> LookupFlag {
53        self.of_unit_type().lookup_flag()
54    }
55
56    /// Different enumerations for GSUB and GPOS
57    pub fn lookup_type(&self) -> u16 {
58        self.of_unit_type().lookup_type()
59    }
60
61    pub fn mark_filtering_set(&self) -> Option<u16> {
62        self.of_unit_type().mark_filtering_set()
63    }
64
65    /// Return the subtables for this lookup.
66    ///
67    /// This method handles both extension and non-extension lookups, and saves
68    /// the caller needing to dig into the `SubstitutionLookup` enum itself.
69    pub fn subtables(&self) -> Result<SubstitutionSubtables<'a>, ReadError> {
70        let raw_lookup = self.of_unit_type();
71        let offsets = raw_lookup.subtable_offsets();
72        let data = raw_lookup.offset_data();
73        match raw_lookup.lookup_type() {
74            1 => Ok(SubstitutionSubtables::Single(Subtables::new(offsets, data))),
75            2 => Ok(SubstitutionSubtables::Multiple(Subtables::new(
76                offsets, data,
77            ))),
78            3 => Ok(SubstitutionSubtables::Alternate(Subtables::new(
79                offsets, data,
80            ))),
81            4 => Ok(SubstitutionSubtables::Ligature(Subtables::new(
82                offsets, data,
83            ))),
84            5 => Ok(SubstitutionSubtables::Contextual(Subtables::new(
85                offsets, data,
86            ))),
87            6 => Ok(SubstitutionSubtables::ChainContextual(Subtables::new(
88                offsets, data,
89            ))),
90            8 => Ok(SubstitutionSubtables::Reverse(Subtables::new(
91                offsets, data,
92            ))),
93            7 => {
94                let first = offsets.first().ok_or(ReadError::OutOfBounds)?.get();
95                let ext: ExtensionSubstFormat1<()> = first.resolve(data)?;
96                match ext.extension_lookup_type() {
97                    1 => Ok(SubstitutionSubtables::Single(Subtables::new_ext(
98                        offsets, data,
99                    ))),
100                    2 => Ok(SubstitutionSubtables::Multiple(Subtables::new_ext(
101                        offsets, data,
102                    ))),
103                    3 => Ok(SubstitutionSubtables::Alternate(Subtables::new_ext(
104                        offsets, data,
105                    ))),
106                    4 => Ok(SubstitutionSubtables::Ligature(Subtables::new_ext(
107                        offsets, data,
108                    ))),
109                    5 => Ok(SubstitutionSubtables::Contextual(Subtables::new_ext(
110                        offsets, data,
111                    ))),
112                    6 => Ok(SubstitutionSubtables::ChainContextual(Subtables::new_ext(
113                        offsets, data,
114                    ))),
115                    8 => Ok(SubstitutionSubtables::Reverse(Subtables::new_ext(
116                        offsets, data,
117                    ))),
118                    other => Err(ReadError::InvalidFormat(other as _)),
119                }
120            }
121            other => Err(ReadError::InvalidFormat(other as _)),
122        }
123    }
124}
read_fonts/tables/gsub.rs

read_fonts/tables/
gsub.rs
