Module: CharWidth

Defined in:
lib/charwidth.rb

Overview

Character-cell width and emoji classification, by Unicode codepoint.

Terminal column width must be a property of the codepoint (not the rendered glyph), so that applications running inside the terminal — which compute their own layout from the same Unicode width — stay in sync. These tables are the canonical East Asian Wide/Fullwidth + emoji blocks (UCD 13.0), curated to the substantial ranges; they’re a couple of KB and drive two decisions:

* width(cp)  -> 1 or 2 cells (wide = CJK/Hangul/Kana/fullwidth + emoji)
* emoji?(cp) -> whether to render in colour (the non-CJK wide blocks)

Combining marks (width 0) are deliberately not handled yet (treated as 1).

Constant Summary collapse

WIDE_SPACER =

Codepoint stored in the second cell of a double-width glyph: a blank, advancing placeholder. The terminal writes it after a wide char so the next column is reserved; the X11 backend renders codepoint 0 as a blank advancing glyph and the bitmap/virtual backends skip it.

0
WIDE =

Wide (two-cell) blocks: CJK, Hangul, Kana, fullwidth forms, and emoji.

[
  0x1100..0x115F, 0x231A..0x232A, 0x23E9..0x23F3, 0x25FD..0x27BF,
  0x2B1B..0x2B55, 0x2E80..0xA4C6, 0xA960..0xA97C, 0xAC00..0xD7A3,
  0xF900..0xFAD9, 0xFE10..0xFE6B, 0xFF01..0xFF60, 0xFFE0..0xFFE6,
  0x16FE0..0x18D08, 0x1B000..0x1B2FB, 0x1F18E..0x1F19A, 0x1F200..0x1F265,
  0x1F300..0x1F5A4, 0x1F5FB..0x1F6FC, 0x1F7E0..0x1F7EB, 0x1F90C..0x1F9FF,
  0x1FA70..0x1FAD6, 0x20000..0x2EBE0, 0x2F800..0x2FA1D, 0x30000..0x3134A
].freeze
EMOJI =

The emoji subset of WIDE (excludes CJK/Hangul/Kana/fullwidth): these render in colour when a colour font provides them. Digits, ‘#’, ‘*’ etc. are not here, so they stay as ordinary text even though Noto maps colour keycaps.

[
  0x231A..0x232A, 0x23E9..0x23F3, 0x25FD..0x27BF, 0x2B1B..0x2B55,
  0x1F18E..0x1F19A, 0x1F200..0x1F265, 0x1F300..0x1F5A4, 0x1F5FB..0x1F6FC,
  0x1F7E0..0x1F7EB, 0x1F90C..0x1F9FF, 0x1FA70..0x1FAD6
].freeze

Class Method Summary collapse

Class Method Details

.emoji?(cp) ⇒ Boolean

Whether a codepoint should render as a colour emoji (when the font has it).

Returns:

  • (Boolean) 


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# File 'lib/charwidth.rb', line 52

def emoji?(cp)
  return false if cp < 0x231A
  in_ranges?(EMOJI, cp)
end

.in_ranges?(ranges, cp) ⇒ Boolean

Binary search over a sorted array of non-overlapping ranges.

Returns:

  • (Boolean) 


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# File 'lib/charwidth.rb', line 58

def in_ranges?(ranges, cp)
  lo = 0
  hi = ranges.length - 1
  while lo <= hi
    mid = (lo + hi) / 2
    r = ranges[mid]
    if cp < r.begin then hi = mid - 1
    elsif cp > r.end then lo = mid + 1
    else return true
    end
  end
  false
end

.wide?(cp) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/charwidth.rb', line 49

def wide?(cp) = width(cp) == 2

.width(cp) ⇒ Object

Number of terminal cells a codepoint occupies (1 or 2).



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# File 'lib/charwidth.rb', line 44

def width(cp)
  return 1 if cp < 0x1100      # fast path: ASCII/Latin and most text
  in_ranges?(WIDE, cp) ? 2 : 1
end