Module: HexaPDF::CExt::ImageLoaderPNG

Defined in:
lib/hexapdf/cext/image_loader_png.rb

Instance Method Summary collapse

Instance Method Details

#separate_alpha_channel(offset, decode_parms) ⇒ Object

Faster version of this method by moving the inner loop to C.



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# File 'lib/hexapdf/cext/image_loader_png.rb', line 8

def separate_alpha_channel(offset, decode_parms)
  bytes_per_colors = (decode_parms[:BitsPerComponent] * decode_parms[:Colors] + 7) / 8
  bytes_per_alpha = (decode_parms[:BitsPerComponent] + 7) / 8
  bytes_per_row = (decode_parms[:Columns] * decode_parms[:BitsPerComponent] *
    (decode_parms[:Colors] + 1) + 7) / 8 + 1
  image_data = ''.b
  mask_data = ''.b

  flate_decode = @document.config.constantize('filter.map', :FlateDecode)
  source = flate_decode.decoder(Fiber.new(&image_data_proc(offset)))
  image_deflate = Zlib::Deflate.new(HexaPDF::GlobalConfiguration['filter.flate_compression'],
                                    Zlib::MAX_WBITS,
                                    HexaPDF::GlobalConfiguration['filter.flate_memory'])
  mask_deflate = Zlib::Deflate.new(HexaPDF::GlobalConfiguration['filter.flate_compression'],
                                   Zlib::MAX_WBITS,
                                   HexaPDF::GlobalConfiguration['filter.flate_memory'])
  data = ''.b
  image_temp = ''.b
  mask_temp = ''.b
  while source.alive? && (new_data = source.resume)
    data << new_data
    image_temp.clear
    mask_temp.clear
    HexaPDFCExt.separate_alpha_channel_loop(data, bytes_per_row, bytes_per_colors,
                                            bytes_per_alpha, image_temp, mask_temp)
    image_data << image_deflate.deflate(image_temp)
    mask_data << mask_deflate.deflate(mask_temp)
  end
  image_data << image_deflate.finish
  mask_data << mask_deflate.finish

  return [image_data, mask_data]
end