OpenType (OTF)

OpenType/CFF uses cubic Bézier curves in a Compact Font Format.

Overview

• Curve Type: Cubic Bézier
• Hinting: PostScript hints
• Storage: CFF table

Key Tables

Table	Purpose
head	Font header
hhea	Horizontal header
maxp	Maximum profile
name	Name records
cmap	Character mapping
CFF	Compact Font Format
hmtx	Horizontal metrics
post	PostScript names
OS/2	OS/2 metrics
GSUB	Glyph substitution
GPOS	Glyph positioning

CFF Table Structure

cff = font.tables['CFF']

# Top DICT
top_dict = cff.top_dicts.first

# Name
puts "Font name: #{cff.names.first}"

# Private DICT
private = top_dict[:private]
puts "Blue values: #{private[:blue_values]}"
puts "Std HW: #{private[:std_hw]}"

CharStrings

cff = font.tables['CFF']

# Access CharStrings
charstrings = cff.charstrings

charstrings.each_with_index do |charstring, glyph_id|
  puts "Glyph #{glyph_id}: #{charstring.length} operators"
end

Hinting

OpenType fonts use PostScript hints:

private = font.tables['CFF'].top_dicts.first[:private]

# Blue zones
puts "Blue values: #{private[:blue_values]}"
puts "Other blues: #{private[:other_blues]}"

# Stem widths
puts "Std HW: #{private[:std_hw]}"
puts "Std VW: #{private[:std_vw]}"
puts "Stem snap H: #{private[:stem_snap_h]}"

Converting

OTF to TTF

fontisan convert font.otf --to ttf --output font.ttf

OTF to WOFF2

fontisan convert font.otf --to woff2 --output font.woff2

Characteristics

Advantages

• Smaller file size — CFF compression
• Cubic curves — Fewer points needed
• PostScript heritage — Print workflows

Limitations

• Limited hinting — PostScript hints vs TrueType
• Variable support — CFF2 required