Class: PureJPEG::BitWriter

Inherits:
Object
  • Object
show all
Defined in:
lib/pure_jpeg/bit_writer.rb

Instance Method Summary collapse

Constructor Details

#initialize ⇒ BitWriter

Returns a new instance of BitWriter.



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# File 'lib/pure_jpeg/bit_writer.rb', line 5

def initialize
  @data = String.new(capacity: 4096, encoding: Encoding::BINARY)
  @buffer = 0
  @bits_in_buffer = 0
end

Instance Method Details

#bytes ⇒ Object 



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# File 'lib/pure_jpeg/bit_writer.rb', line 34

def bytes
  @data
end

#flush ⇒ Object

Pad remaining bits with 1s and flush (per JPEG spec).



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# File 'lib/pure_jpeg/bit_writer.rb', line 28

def flush
  return unless @bits_in_buffer > 0
  padding = 8 - @bits_in_buffer
  write_bits((1 << padding) - 1, padding)
end

#write_bits(value, num_bits) ⇒ Object

Write ‘num_bits` of `value` (MSB first) into the output stream.



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# File 'lib/pure_jpeg/bit_writer.rb', line 12

def write_bits(value, num_bits)
  return if num_bits == 0
  @buffer = (@buffer << num_bits) | (value & ((1 << num_bits) - 1))
  @bits_in_buffer += num_bits

  while @bits_in_buffer >= 8
    @bits_in_buffer -= 8
    byte = (@buffer >> @bits_in_buffer) & 0xFF
    @data << byte
    @data << 0x00 if byte == 0xFF  # byte stuffing
  end

  @buffer &= (1 << @bits_in_buffer) - 1
end