Class: FastImageParsing::Jxlc

Inherits:
Object
  • Object
show all
Defined in:
lib/fastimage/fastimage_parsing/jxlc.rb

Overview

:nodoc:

Constant Summary collapse

LENGTHS = 
[9, 13, 18, 30]
MULTIPLIERS = 
[1, 1.2, Rational(4, 3), 1.5, Rational(16, 9), 1.25, 2]

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(stream) ⇒ Jxlc

Returns a new instance of Jxlc.



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# File 'lib/fastimage/fastimage_parsing/jxlc.rb', line 8

def initialize(stream)
  @stream = stream
  @width, @height´ = nil
  @bit_counter = 0
  parse_jxlc
end

Instance Attribute Details

#height ⇒ Object (readonly)

Returns the value of attribute height.



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# File 'lib/fastimage/fastimage_parsing/jxlc.rb', line 3

def height
  @height
end

#width ⇒ Object (readonly)

Returns the value of attribute width.



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# File 'lib/fastimage/fastimage_parsing/jxlc.rb', line 3

def width
  @width
end

Instance Method Details

#get_bits(size) ⇒ Object 



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# File 'lib/fastimage/fastimage_parsing/jxlc.rb', line 40

def get_bits(size)
  if @words.size < (@bit_counter + size) / 16 + 1
    @words += @stream.read(4).unpack('vv')
  end

  dest_pos = 0
  dest = 0
  size.times do
    word = @bit_counter / 16
    source_pos = @bit_counter % 16
    dest |= ((@words[word] & (1 << source_pos)) > 0 ? 1 : 0) << dest_pos
    dest_pos += 1
    @bit_counter += 1
  end
  dest
end

#parse_jxlc ⇒ Object 



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# File 'lib/fastimage/fastimage_parsing/jxlc.rb', line 15

def parse_jxlc
  @words = @stream.read(6)[2..5].unpack('vv')

  # small mode allows for values <= 256 that are divisible by 8
  small = get_bits(1)
  if small == 1
    y = (get_bits(5) + 1) * 8
    x = x_from_ratio(y)
    if !x
      x = (get_bits(5) + 1) * 8
    end
    @width, @height = x, y
    return
  end

  len = LENGTHS[get_bits(2)]
  y = get_bits(len) + 1
  x = x_from_ratio(y)
  if !x
    len = LENGTHS[get_bits(2)]
    x = get_bits(len) + 1
  end
  @width, @height = x, y
end

#x_from_ratio(y) ⇒ Object 



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# File 'lib/fastimage/fastimage_parsing/jxlc.rb', line 57

def x_from_ratio(y)
  ratio = get_bits(3)
  if ratio == 0
    return nil
  else
    return (y * MULTIPLIERS[ratio - 1]).to_i
  end
end