Class: ZplRender::TrueType

Inherits:
Object
  • Object
show all
Defined in:
lib/zpl_render/truetype.rb

Overview

Minimal pure-Ruby TrueType font loader and glyph rasterizer.

Parses just enough of a .ttf (head, maxp, cmap format 4, loca, glyf, hhea, hmtx, OS/2) to rasterize glyph outlines: quadratic contours are flattened to polygons and filled scanline-wise with the non-zero winding rule, sampling at pixel centers. Output is 1-bit, matching a thermal print head.

Defined Under Namespace

Classes: Glyph

Constant Summary collapse

ON_CURVE = 
0x01
X_SHORT = 
0x02
Y_SHORT = 
0x04
REPEAT = 
0x08
X_SAME_OR_POS = 
0x10
Y_SAME_OR_POS = 
0x20
CURVE_SEGMENTS =

polyline segments per quadratic bezier

8

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(path) ⇒ TrueType

Returns a new instance of TrueType.



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# File 'lib/zpl_render/truetype.rb', line 33

def initialize(path)
  @data = File.binread(path)
  @tables = parse_table_directory
  parse_head
  parse_maxp
  parse_hhea_hmtx
  parse_cmap
  parse_os2
  @glyph_cache = {}
  @contour_cache = {}
end

Instance Attribute Details

#cap_height ⇒ Object (readonly)

Returns the value of attribute cap_height.



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# File 'lib/zpl_render/truetype.rb', line 23

def cap_height
  @cap_height
end

#units_per_em ⇒ Object (readonly)

Returns the value of attribute units_per_em.



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# File 'lib/zpl_render/truetype.rb', line 23

def units_per_em
  @units_per_em
end

Class Method Details

.default ⇒ Object 



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# File 'lib/zpl_render/truetype.rb', line 25

def self.default
  @default ||= new(File.expand_path("fonts/LiberationSans-Bold.ttf", __dir__))
end

.mono ⇒ Object 



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# File 'lib/zpl_render/truetype.rb', line 29

def self.mono
  @mono ||= new(File.expand_path("fonts/LiberationMono-Regular.ttf", __dir__))
end

Instance Method Details

#advance(code) ⇒ Object

Advance width in font units for a unicode codepoint.



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# File 'lib/zpl_render/truetype.rb', line 46

def advance(code)
  gid = glyph_id(code)
  @advances[gid] || @advances.last || @units_per_em / 2
end

#glyph_bitmap(code, scale_x, scale_y) ⇒ Object

Rasterize a glyph at the given x/y scales (pixels per font unit). Returns a Glyph whose canvas is stamped at (pen_x + left, baseline_y - top). Returns nil for blank glyphs.



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# File 'lib/zpl_render/truetype.rb', line 58

def glyph_bitmap(code, scale_x, scale_y)
  key = [code, (scale_x * 10_000).round, (scale_y * 10_000).round]
  return @glyph_cache[key] if @glyph_cache.key?(key)

  @glyph_cache[key] = rasterize(glyph_id(code), scale_x, scale_y)
end

#glyph_id(code) ⇒ Object 



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# File 'lib/zpl_render/truetype.rb', line 51

def glyph_id(code)
  @cmap_cache[code] ||= lookup_cmap(code)
end