Module: ZPNG::BMP::Reader

Included in:

Image

Defined in:

lib/zpng/bmp/reader.rb

Instance Method Summary

• #_read_bmp(io) ⇒ Object

  en.wikipedia.org/wiki/BMP_file_format.

Instance Method Details

#_read_bmp(io) ⇒ Object

en.wikipedia.org/wiki/BMP_file_format

# File 'lib/zpng/bmp/reader.rb', line 157

def _read_bmp io
  fhdr = BITMAPFILEHEADER.read(io)
  # DIB Header immediately follows the Bitmap File Header
  ihdr = BITMAPINFOHEADER.read(io)
  if ihdr.biSize != BITMAPINFOHEADER::SIZE
    raise "dib_hdr_size #{ihdr.biSize} unsupported, want #{BITMAPINFOHEADER::SIZE}"
  end

  @new_image = true
  @color_class = BMP::Color
  @format = :bmp
  @chunks << BmpPseudoChunk.new(fhdr)
  @chunks << BmpHdrPseudoChunk.new(ihdr)

  # http://en.wikipedia.org/wiki/BMP_file_format#Pixel_storage
  row_size = ((ihdr.biBitCount*self.width+31)/32)*4

  gap1_size = fhdr.bfOffBits - io.tell

  STDERR.puts "[?] negative gap1=#{gap1_size}".red if gap1_size < 0

  if ihdr.biBitCount == 8 && gap1_size >= 1024
    # palette for 256-color BMP
    data = io.read 1024
    @chunks << BmpPaletteChunk.new(data)
    gap1_size -= 1024
  end

  if gap1_size != 0
    @chunks << BmpPseudoChunk.new(
      TypedBlock.new("GAP1", gap1_size, io.tell, io.read(gap1_size))
    )
    #io.seek(fhdr.bfOffBits)
  end

  pos0 = io.tell
  @scanlines = []
  self.height.times do |idx|
    offset = io.tell - fhdr.bfOffBits
    data = io.read(row_size)
    # BMP scanlines layout is upside-down
    @scanlines.unshift ScanLine.new(self, self.height-idx-1,
                                    :decoded_bytes => data,
                                    :size   => row_size,
                                    :offset => offset
                                   )
  end

  @chunks << BmpPseudoChunk.new(
      TypedBlock.new("IMAGEDATA", io.tell - pos0, pos0, '')
  )

  unless io.eof?
    @chunks << BmpPseudoChunk.new(
      TypedBlock.new("GAP2", io.size - io.tell, io.tell, '')
    )
  end

  extend ImageMixin
end