5c2ecee60f
flash files can be quite big (the biggest on danbooru.donmai.us being 68.6MB atm). Reading it and applying complex transformations twice seems unnecessary.
59 lines
2.1 KiB
Ruby
59 lines
2.1 KiB
Ruby
# Adapted from https://github.com/dim/ruby-imagespec/blob/f2f3ce8bb5b1b411f8658e66a891a095261d94c0/lib/image_spec/parser/swf.rb
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# License: https://github.com/dim/ruby-imagespec/blob/master/LICENSE
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class MediaFile::Flash < MediaFile
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def dimensions
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# Read the entire stream into memory because the
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# dimensions aren't stored in a standard location
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contents = File.read(file.path, binmode: true).force_encoding("ASCII-8BIT")
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# Our 'signature' is the first 3 bytes
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# Either FWS or CWS. CWS indicates compression
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signature = contents[0..2]
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# SWF version
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version = contents[3].unpack('C').join.to_i
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# Determine the length of the uncompressed stream
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length = contents[4..7].unpack('V').join.to_i
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# If we do, in fact, have compression
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if signature == 'CWS'
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# Decompress the body of the SWF
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body = Zlib::Inflate.inflate( contents[8..length] )
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# And reconstruct the stream contents to the first 8 bytes (header)
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# Plus our decompressed body
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contents = contents[0..7] + body
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end
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# Determine the nbits of our dimensions rectangle
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nbits = contents.unpack('C'*contents.length)[8] >> 3
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# Determine how many bits long this entire RECT structure is
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rectbits = 5 + nbits * 4 # 5 bits for nbits, as well as nbits * number of fields (4)
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# Determine how many bytes rectbits composes (ceil(rectbits/8))
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rectbytes = (rectbits.to_f / 8).ceil
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# Unpack the RECT structure from the stream in little-endian bit order, then join it into a string
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rect = contents[8..(8 + rectbytes)].unpack("#{'B8' * rectbytes}").join
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# Read in nbits incremenets starting from 5
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dimensions = Array.new
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4.times do |n|
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s = 5 + (n * nbits) # Calculate our start index
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e = s + (nbits - 1) # Calculate our end index
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dimensions[n] = rect[s..e].to_i(2) # Read that range (binary) and convert it to an integer
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end
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# The values we have here are in "twips"
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# 20 twips to a pixel (that's why SWFs are fuzzy sometimes!)
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width = (dimensions[1] - dimensions[0]) / 20
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height = (dimensions[3] - dimensions[2]) / 20
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[width, height]
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end
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memoize :dimensions
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end
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