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Diffstat (limited to 'src')
| -rw-r--r-- | src/Text/Pandoc/ImageSize.hs | 110 |
1 files changed, 110 insertions, 0 deletions
diff --git a/src/Text/Pandoc/ImageSize.hs b/src/Text/Pandoc/ImageSize.hs new file mode 100644 index 000000000..48731acf8 --- /dev/null +++ b/src/Text/Pandoc/ImageSize.hs @@ -0,0 +1,110 @@ +{-# LANGUAGE OverloadedStrings, ScopedTypeVariables #-} +{- +Copyright (C) 2011 John MacFarlane <jgm@berkeley.edu> + +This program is free software; you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation; either version 2 of the License, or +(at your option) any later version. + +This program is distributed in the hope that it will be useful, +but WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +GNU General Public License for more details. + +You should have received a copy of the GNU General Public License +along with this program; if not, write to the Free Software +Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA +-} + +{- | + Module : Text.Pandoc.ImageSize + Copyright : Copyright (C) 2011 John MacFarlane + License : GNU GPL, version 2 or above + + Maintainer : John MacFarlane <jgm@berkeley.edu> + Stability : alpha + Portability : portable + +Functions for determining the size of a PNG, JPEG, or GIF image. + +Algorithms borrowwed from wwwis.pl (c) 2005 Alex K, released +under the GPL. +-} +module Text.Pandoc.ImageSize ( imageType, imageSize, readImageSize ) where +import Data.ByteString.Lazy (ByteString, unpack) +import qualified Data.ByteString.Lazy.Char8 as B +import Control.Monad +import Data.Bits + +-- quick and dirty functions to get image sizes +-- algorithms borrowed from wwwis.pl + +data ImageType = Png | Gif | Jpeg deriving Show + +type Height = Integer +type Width = Integer + +readImageSize :: FilePath -> IO (Maybe (Width,Height)) +readImageSize fp = imageSize `fmap` B.readFile fp + +imageType :: ByteString -> Maybe ImageType +imageType img = case B.take 4 img of + "\x89\x50\x4e\x47" -> return Png + "\x47\x49\x46\x38" -> return Gif + "\xff\xd8\xff\xe0" -> return Jpeg + _ -> fail "Unknown image type" + +imageSize :: ByteString -> Maybe (Width,Height) +imageSize img = do + t <- imageType img + case t of + Png -> pngSize img + Gif -> gifSize img + Jpeg -> jpegSize img + +pngSize :: ByteString -> Maybe (Width,Height) +pngSize img = do + let (h, rest) = B.splitAt 8 img + guard $ h == "\x8a\x4d\x4e\x47\x0d\x0a\x1a\x0a" || + h == "\x89\x50\x4e\x47\x0d\x0a\x1a\x0a" + let (i, rest') = B.splitAt 4 $ B.drop 4 rest + guard $ i == "MHDR" || i == "IHDR" + case map fromIntegral $ unpack $ B.take 8 rest' of + ([w1,w2,w3,w4,h1,h2,h3,h4] :: [Integer]) -> return + ((shift w1 24) + (shift w2 16) + (shift w3 8) + w4, + (shift h1 24) + (shift h2 16) + (shift h3 8) + h4) + _ -> fail "PNG parse error" + +gifSize :: ByteString -> Maybe (Width,Height) +gifSize img = do + let (h, rest) = B.splitAt 6 img + guard $ h == "GIF87a" || h == "GIF89a" + case map fromIntegral $ unpack $ B.take 4 rest of + [w2,w1,h2,h1] -> return (shift w1 8 + w2, shift h1 8 + h2) + _ -> fail "GIF parse error" + +jpegSize :: ByteString -> Maybe (Width,Height) +jpegSize img = do + let (h, rest) = B.splitAt 2 img + guard $ h == "\xff\xd8" + findJpegLength rest + +findJpegLength :: ByteString -> Maybe (Width,Height) +findJpegLength bs = do + let bs' = B.dropWhile (=='\xff') $ B.dropWhile (/='\xff') bs + case B.uncons bs' of + Just (c,bs'') | c >= '\xc0' && c <= '\xc3' -> do + case map fromIntegral $ unpack $ B.take 4 $ B.drop 3 bs'' of + [h1,h2,w1,w2] -> return (shift w1 8 + w2, shift h1 8 + h2) + _ -> fail "JPEG parse error" + Just (_,bs'') -> do + case map fromIntegral $ unpack $ B.take 2 bs'' of + [c1,c2] -> do + let len = shift c1 8 + c2 + -- skip variables + findJpegLength $ B.drop len bs'' + _ -> fail "JPEG parse error" + Nothing -> fail "Did not find length record" + + |