ttf_parser/tables/
head.rs

1//! A [Font Header Table](
2//! https://docs.microsoft.com/en-us/typography/opentype/spec/head) implementation.
3
4use crate::parser::{Fixed, Stream};
5use crate::Rect;
6
7/// An index format used by the [Index to Location Table](
8/// https://docs.microsoft.com/en-us/typography/opentype/spec/loca).
9#[allow(missing_docs)]
10#[derive(Clone, Copy, PartialEq, Eq, Debug)]
11pub enum IndexToLocationFormat {
12    Short,
13    Long,
14}
15
16/// A [Font Header Table](https://docs.microsoft.com/en-us/typography/opentype/spec/head).
17#[derive(Clone, Copy, Debug)]
18pub struct Table {
19    /// Units per EM.
20    ///
21    /// Guarantee to be in a 16..=16384 range.
22    pub units_per_em: u16,
23    /// A bounding box that large enough to enclose any glyph from the face.
24    pub global_bbox: Rect,
25    /// An index format used by the [Index to Location Table](
26    /// https://docs.microsoft.com/en-us/typography/opentype/spec/loca).
27    pub index_to_location_format: IndexToLocationFormat,
28}
29
30impl Table {
31    /// Parses a table from raw data.
32    pub fn parse(data: &[u8]) -> Option<Self> {
33        // Do not check the exact length, because some fonts include
34        // padding in table's length in table records, which is incorrect.
35        if data.len() < 54 {
36            return None;
37        }
38
39        let mut s = Stream::new(data);
40        s.skip::<u32>(); // version
41        s.skip::<Fixed>(); // font revision
42        s.skip::<u32>(); // checksum adjustment
43        s.skip::<u32>(); // magic number
44        s.skip::<u16>(); // flags
45        let units_per_em = s.read::<u16>()?;
46        s.skip::<u64>(); // created time
47        s.skip::<u64>(); // modified time
48        let x_min = s.read::<i16>()?;
49        let y_min = s.read::<i16>()?;
50        let x_max = s.read::<i16>()?;
51        let y_max = s.read::<i16>()?;
52        s.skip::<u16>(); // mac style
53        s.skip::<u16>(); // lowest PPEM
54        s.skip::<i16>(); // font direction hint
55        let index_to_location_format = s.read::<u16>()?;
56
57        if !(16..=16384).contains(&units_per_em) {
58            return None;
59        }
60
61        let index_to_location_format = match index_to_location_format {
62            0 => IndexToLocationFormat::Short,
63            1 => IndexToLocationFormat::Long,
64            _ => return None,
65        };
66
67        Some(Table {
68            units_per_em,
69            global_bbox: Rect {
70                x_min,
71                y_min,
72                x_max,
73                y_max,
74            },
75            index_to_location_format,
76        })
77    }
78}
ttf_parser/tables/head.rs

ttf_parser/tables/
head.rs
