Module: Fontisan::Ufo::Compile::Hhea

Defined in:
lib/fontisan/ufo/compile/hhea.rb

Overview

Builds the OpenType hhea (horizontal header) table.

See Also:

Constant Summary collapse

VERSION_1_0 = 
0x00010000

Class Method Summary collapse

Class Method Details

.build(font, glyphs:) ⇒ Fontisan::Tables::Hhea

Parameters:

Returns:



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
 
# File 'lib/fontisan/ufo/compile/hhea.rb', line 14

def self.build(font, glyphs:)
  info = font.info
  widths = glyphs.map { |g| g.width.to_i }

  # Calculate real LSB/RSB/extent from glyph bounding boxes
  # instead of hardcoding 0. These values help layout engines
  # optimize text rendering and detect clipping.
  min_lsb = nil
  min_rsb = nil
  max_extent = nil

  glyphs.each do |glyph|
    w = glyph.width.to_i
    bbox = glyph.bbox
    next unless bbox

    xmin = bbox.x_min.to_i
    xmax = bbox.x_max.to_i
    min_lsb = xmin if min_lsb.nil? || xmin < min_lsb
    rsb = w - xmax
    min_rsb = rsb if min_rsb.nil? || rsb < min_rsb
    max_extent = xmax if max_extent.nil? || xmax > max_extent
  end

  Fontisan::Tables::Hhea.new(
    version_raw: VERSION_1_0,
    ascent: info.ascender || 800,
    descent: info.descender || -200,
    line_gap: info.open_type_hhea_line_gap || 0,
    advance_width_max: widths.max || 0,
    min_left_side_bearing: min_lsb || 0,
    min_right_side_bearing: min_rsb || 0,
    x_max_extent: max_extent || 0,
    caret_slope_rise: 1,
    caret_slope_run: 0,
    caret_offset: 0,
    metric_data_format: 0,
    number_of_h_metrics: glyphs.size,
  )
end