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}
79