-- | Convert GIF images to PPM images
module GIF2PPM(gif2ppm) where
import GIF
import PNM
import Data.Array
import Data.List(sortOn)
import Utils2(pieces)

gif2ppm gif = PNM (w,h) (PPM 255 rgbs)
  where
    sd = screen_descriptor gif
    w = fromEnum (swidth sd)
    h = fromEnum (sheight sd)

    scmap = maybe (const (RGB 255 0 0)) (!) $
            fmap (cmap (sbitsPerPixel sd)) (global_color_map gif)

    rgbs =
      case [(i,deinterlaced_raster_data i) | Right i <- data_blocks gif] of
        (i,r):_ -> map icmap r
	  where
	    id = image_descriptor i
	    icmap = maybe scmap ((!) . cmap (ibitsPerPixel id)) (local_colorMap i)

cmap bits = listArray (0,2^bits-1) . map (fmap fromEnum)

deinterlaced_raster_data image =
  (if interlace d
  then deinterlace (iwidth d) (iheight d)
  else id) (raster_data image)
  where
    d = image_descriptor image

deinterlace :: Short -> Short -> Pixels -> Pixels
deinterlace w h pixels = concat . reorder . lines $ pixels
  where
    lines = pieces (fromEnum w)
    reorder = map snd . sortOn fst . zip poslist
    poslist = [0,8..l]++[4,12..l]++[2,6..l]++[1,3..l]
    l=h-1