ttf_parser/ggg/
lookup.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
use crate::parser::{
    FromData, FromSlice, LazyArray16, LazyOffsetArray16, Offset, Offset16, Offset32, Stream,
};

/// A list of [`Lookup`] values.
pub type LookupList<'a> = LazyOffsetArray16<'a, Lookup<'a>>;

/// A [Lookup Table](https://docs.microsoft.com/en-us/typography/opentype/spec/chapter2#lookup-table).
#[derive(Clone, Copy, Debug)]
pub struct Lookup<'a> {
    /// Lookup qualifiers.
    pub flags: LookupFlags,
    /// Available subtables.
    pub subtables: LookupSubtables<'a>,
    /// Index into GDEF mark glyph sets structure.
    pub mark_filtering_set: Option<u16>,
}

impl<'a> FromSlice<'a> for Lookup<'a> {
    fn parse(data: &'a [u8]) -> Option<Self> {
        let mut s = Stream::new(data);
        let kind = s.read::<u16>()?;
        let flags = s.read::<LookupFlags>()?;
        let count = s.read::<u16>()?;
        let offsets = s.read_array16(count)?;

        let mut mark_filtering_set: Option<u16> = None;
        if flags.use_mark_filtering_set() {
            mark_filtering_set = Some(s.read::<u16>()?);
        }

        Some(Self {
            flags,
            subtables: LookupSubtables {
                kind,
                data,
                offsets,
            },
            mark_filtering_set,
        })
    }
}

/// A trait for parsing Lookup subtables.
///
/// Internal use only.
pub trait LookupSubtable<'a>: Sized {
    /// Parses raw data.
    fn parse(data: &'a [u8], kind: u16) -> Option<Self>;
}

/// A list of lookup subtables.
#[derive(Clone, Copy)]
pub struct LookupSubtables<'a> {
    kind: u16,
    data: &'a [u8],
    offsets: LazyArray16<'a, Offset16>,
}

impl core::fmt::Debug for LookupSubtables<'_> {
    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
        write!(f, "LookupSubtables {{ ... }}")
    }
}

impl<'a> LookupSubtables<'a> {
    /// Returns a number of items in the LookupSubtables.
    #[inline]
    pub fn len(&self) -> u16 {
        self.offsets.len()
    }

    /// Checks if there are any items.
    pub fn is_empty(&self) -> bool {
        self.offsets.is_empty()
    }

    /// Parses a subtable at index.
    ///
    /// Accepts either
    /// [`PositioningSubtable`](crate::gpos::PositioningSubtable)
    /// or [`SubstitutionSubtable`](crate::gsub::SubstitutionSubtable).
    ///
    /// Technically, we can enforce it at compile time, but it makes code too convoluted.
    pub fn get<T: LookupSubtable<'a>>(&self, index: u16) -> Option<T> {
        let offset = self.offsets.get(index)?.to_usize();
        let data = self.data.get(offset..)?;
        T::parse(data, self.kind)
    }

    /// Creates an iterator over subtables.
    ///
    /// We cannot use `IntoIterator` here, because we have to use user-provided base type.
    #[allow(clippy::should_implement_trait)]
    pub fn into_iter<T: LookupSubtable<'a>>(self) -> LookupSubtablesIter<'a, T> {
        LookupSubtablesIter {
            data: self,
            index: 0,
            data_type: core::marker::PhantomData,
        }
    }
}

/// An iterator over lookup subtables.
#[allow(missing_debug_implementations)]
pub struct LookupSubtablesIter<'a, T: LookupSubtable<'a>> {
    data: LookupSubtables<'a>,
    index: u16,
    data_type: core::marker::PhantomData<T>,
}

impl<'a, T: LookupSubtable<'a>> Iterator for LookupSubtablesIter<'a, T> {
    type Item = T;

    fn next(&mut self) -> Option<Self::Item> {
        if self.index < self.data.len() {
            self.index += 1;
            self.data.get(self.index - 1)
        } else {
            None
        }
    }
}

/// Lookup table flags.
#[allow(missing_docs)]
#[derive(Clone, Copy, Debug)]
pub struct LookupFlags(pub u16);

#[rustfmt::skip]
#[allow(missing_docs)]
impl LookupFlags {
    #[inline] pub fn right_to_left(self) -> bool { self.0 & 0x0001 != 0 }
    #[inline] pub fn ignore_base_glyphs(self) -> bool { self.0 & 0x0002 != 0 }
    #[inline] pub fn ignore_ligatures(self) -> bool { self.0 & 0x0004 != 0 }
    #[inline] pub fn ignore_marks(self) -> bool { self.0 & 0x0008 != 0 }
    #[inline] pub fn ignore_flags(self) -> bool { self.0 & 0x000E != 0 }
    #[inline] pub fn use_mark_filtering_set(self) -> bool { self.0 & 0x0010 != 0 }
    #[inline] pub fn mark_attachment_type(self) -> u8 { ((self.0 & 0xFF00) >> 8) as u8 }
}

impl FromData for LookupFlags {
    const SIZE: usize = 2;

    #[inline]
    fn parse(data: &[u8]) -> Option<Self> {
        u16::parse(data).map(Self)
    }
}

pub(crate) fn parse_extension_lookup<'a, T: 'a>(
    data: &'a [u8],
    parse: impl FnOnce(&'a [u8], u16) -> Option<T>,
) -> Option<T> {
    let mut s = Stream::new(data);
    let format = s.read::<u16>()?;
    match format {
        1 => {
            let kind = s.read::<u16>()?;
            let offset = s.read::<Offset32>()?.to_usize();
            parse(data.get(offset..)?, kind)
        }
        _ => None,
    }
}