Module: ZPNG::BMP::Reader

Included in:
Image
Defined in:
lib/zpng/bmp/reader.rb

Instance Method Summary collapse

Instance Method Details

#_read_bmp(io) ⇒ Object

en.wikipedia.org/wiki/BMP_file_format



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# File 'lib/zpng/bmp/reader.rb', line 70

def _read_bmp io
  filesize, reserved1, reserved2, imagedata_offset = io.read(4+2+2+4).unpack('VvvV')
  # DIB Header immediately follows the Bitmap File Header
  hdr = BITMAPINFOHEADER.read(io)
  if hdr.biSize != BITMAPINFOHEADER::SIZE
    raise "dib_hdr_size #{hdr.biSize} unsupported, want #{BITMAPINFOHEADER::SIZE}"
  end

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

  # http://en.wikipedia.org/wiki/BMP_file_format#Pixel_storage
  row_size = ((hdr.biBitCount*self.width+31)/32)*4
  # XXX hidden data in non-significant tail bits/bytes

  io.seek(imagedata_offset)

  @scanlines = []
  self.height.times do |idx|
    offset = io.tell - imagedata_offset
    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

  extend ImageMixin
end