Class: IpaReader::PngFile

Inherits:
Object
  • Object
show all
Defined in:
lib/ipa_reader/png_file.rb

Class Method Summary collapse

Class Method Details

.normalize_png(oldPNG) ⇒ Object 



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# File 'lib/ipa_reader/png_file.rb', line 6

def self.normalize_png(oldPNG)
  pngheader = "\x89PNG\r\n\x1a\n"

  if oldPNG[0...8] != pngheader
    return nil
  end

  newPNG = oldPNG[0...8]
  
  chunkPos = newPNG.length
  
  # For each chunk in the PNG file
  while chunkPos < oldPNG.length
    
    # Reading chunk
    chunkLength = oldPNG[chunkPos...chunkPos+4]
    chunkLength = chunkLength.unpack("N")[0]
    chunkType = oldPNG[chunkPos+4...chunkPos+8]
    chunkData = oldPNG[chunkPos+8...chunkPos+8+chunkLength]
    chunkCRC = oldPNG[chunkPos+chunkLength+8...chunkPos+chunkLength+12]
    chunkCRC = chunkCRC.unpack("N")[0]
    chunkPos += chunkLength + 12

    # Parsing the header chunk
    if chunkType == "IHDR"
      width = chunkData[0...4].unpack("N")[0]
      height = chunkData[4...8].unpack("N")[0]
    end

    # Parsing the image chunk
    if chunkType == "IDAT"
      # Uncompressing the image chunk
      inf = Zlib::Inflate.new(-Zlib::MAX_WBITS)
      chunkData = inf.inflate(chunkData)
      inf.finish
      inf.close
  
      # Swapping red & blue bytes for each pixel
      newdata = ""
  
      height.times do 
        i = newdata.length
        newdata += chunkData[i..i].to_s
        width.times do
          i = newdata.length
          newdata += chunkData[i+2..i+2].to_s
          newdata += chunkData[i+1..i+1].to_s
          newdata += chunkData[i+0..i+0].to_s
          newdata += chunkData[i+3..i+3].to_s
        end
      end

      # Compressing the image chunk
      chunkData = newdata
      chunkData = Zlib::Deflate.deflate( chunkData )
      chunkLength = chunkData.length
      chunkCRC = Zlib.crc32(chunkType)
      chunkCRC = Zlib.crc32(chunkData, chunkCRC)
      chunkCRC = (chunkCRC + 0x100000000) % 0x100000000
    end

    # Removing CgBI chunk 
    if chunkType != "CgBI"
      newPNG += [chunkLength].pack("N")
      newPNG += chunkType
      if chunkLength > 0
        newPNG += chunkData
      end
      newPNG += [chunkCRC].pack("N")
    end

    # Stopping the PNG file parsing
    if chunkType == "IEND"
      break
    end
  end
   
  return newPNG
end