Class: ImageSpec::Parser::SWF

Inherits:
Object
  • Object
show all
Defined in:
lib/image_spec/parser/swf.rb

Constant Summary collapse

CONTENT_TYPE = 
'application/x-shockwave-flash'

Class Method Summary collapse

Class Method Details

.attributes(stream) ⇒ Object 



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# File 'lib/image_spec/parser/swf.rb', line 7

def self.attributes(stream)
  width, height, version = dimensions(stream)
  {:width => width, :height => height, :content_type => CONTENT_TYPE, :version => version, :dimensions => [width, height], :file_size => size(stream)}
end

.detected?(stream) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/image_spec/parser/swf.rb', line 12

def self.detected?(stream)
  stream.rewind
  stream.read(3) =~ /(F|C)WS/ ? true : false
end

.dimensions(stream) ⇒ Object 



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# File 'lib/image_spec/parser/swf.rb', line 17

def self.dimensions(stream)
  # Read the entire stream into memory because the
  # dimensions aren't stored in a standard location
  stream.rewind
  contents = stream.read.force_encoding("ASCII-8BIT")

  # Our 'signature' is the first 3 bytes
  # Either FWS or CWS.  CWS indicates compression
  signature = contents[0..2]

  # SWF version
  version = contents[3].unpack('C').join.to_i

  # Determine the length of the uncompressed stream
  length = contents[4..7].unpack('V').join.to_i

  # If we do, in fact, have compression
  if signature == 'CWS'
    # Decompress the body of the SWF
    body = Zlib::Inflate.inflate( contents[8..length] )

    # And reconstruct the stream contents to the first 8 bytes (header)
    # Plus our decompressed body
    contents = contents[0..7] + body
  end

  # Determine the nbits of our dimensions rectangle
  nbits = contents.unpack('C'*contents.length)[8] >> 3

  # Determine how many bits long this entire RECT structure is
  rectbits = 5 + nbits * 4    # 5 bits for nbits, as well as nbits * number of fields (4)

  # Determine how many bytes rectbits composes (ceil(rectbits/8))
  rectbytes = (rectbits.to_f / 8).ceil

  # Unpack the RECT structure from the stream in little-endian bit order, then join it into a string
  rect = contents[8..(8 + rectbytes)].unpack("#{'B8' * rectbytes}").join()

  # Read in nbits incremenets starting from 5
  dimensions = Array.new
  4.times do |n|
    s = 5 + (n * nbits)     # Calculate our start index
    e = s + (nbits - 1)     # Calculate our end index
    dimensions[n] = rect[s..e].to_i(2)    # Read that range (binary) and convert it to an integer
  end

  # The values we have here are in "twips"
  # 20 twips to a pixel (that's why SWFs are fuzzy sometimes!)
  width   = (dimensions[1] - dimensions[0]) / 20
  height  = (dimensions[3] - dimensions[2]) / 20

  # If you can't figure this one out, you probably shouldn't have read this far
  return [width, height, version]
end

.size(stream) ⇒ Object 



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# File 'lib/image_spec/parser/swf.rb', line 72

def self.size(stream)
  stream.size
end