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1//! `hhea` — Horizontal Header table.
2//!
3//! Contains global horizontal layout metrics.
4//! Reference: <https://learn.microsoft.com/en-us/typography/opentype/spec/hhea>
5
6use crate::font::parse::Reader;
7use crate::font::FontError;
8
9/// Parsed `hhea` table.
10#[derive(Debug)]
11pub struct HheaTable {
12 /// Typographic ascent (in font units).
13 pub ascent: i16,
14 /// Typographic descent (typically negative, in font units).
15 pub descent: i16,
16 /// Typographic line gap (in font units).
17 pub line_gap: i16,
18 /// Maximum advance width across all glyphs.
19 pub advance_width_max: u16,
20 /// Minimum left side bearing across all glyphs.
21 pub min_left_side_bearing: i16,
22 /// Minimum right side bearing across all glyphs.
23 pub min_right_side_bearing: i16,
24 /// Maximum x extent (max(lsb + (xMax - xMin))).
25 pub x_max_extent: i16,
26 /// Number of entries in the hmtx table's longHorMetric array.
27 pub num_long_hor_metrics: u16,
28}
29
30impl HheaTable {
31 /// Parse the `hhea` table from raw bytes.
32 pub fn parse(data: &[u8]) -> Result<HheaTable, FontError> {
33 let r = Reader::new(data);
34 if r.len() < 36 {
35 return Err(FontError::MalformedTable("hhea"));
36 }
37
38 // skip version(4)
39 let ascent = r.i16(4)?;
40 let descent = r.i16(6)?;
41 let line_gap = r.i16(8)?;
42 let advance_width_max = r.u16(10)?;
43 let min_left_side_bearing = r.i16(12)?;
44 let min_right_side_bearing = r.i16(14)?;
45 let x_max_extent = r.i16(16)?;
46 // skip caretSlopeRise(2), caretSlopeRun(2), caretOffset(2), reserved(8), metricDataFormat(2)
47 let num_long_hor_metrics = r.u16(34)?;
48
49 Ok(HheaTable {
50 ascent,
51 descent,
52 line_gap,
53 advance_width_max,
54 min_left_side_bearing,
55 min_right_side_bearing,
56 x_max_extent,
57 num_long_hor_metrics,
58 })
59 }
60}