module ChunkyPNG::Canvas::PNGDecoding

def decode_png_scanline(filter, bytes, previous_bytes, pixelsize = 3)
  case filter
  when ChunkyPNG::FILTER_NONE    then decode_png_scanline_none(    bytes, previous_bytes, pixelsize)
  when ChunkyPNG::FILTER_SUB     then decode_png_scanline_sub(     bytes, previous_bytes, pixelsize)
  when ChunkyPNG::FILTER_UP      then decode_png_scanline_up(      bytes, previous_bytes, pixelsize)
  when ChunkyPNG::FILTER_AVERAGE then decode_png_scanline_average( bytes, previous_bytes, pixelsize)
  when ChunkyPNG::FILTER_PAETH   then decode_png_scanline_paeth(   bytes, previous_bytes, pixelsize)
  else raise "Unknown filter type"
  end
end