I'm playing a bit with Repa library and its DevIL bindings. I tried to modify
one of the examples
from tutorial on HaskellWiki. I want to load an image, rotate it and save it to
disk. I managed
to write something like this:
import Foreign.Ptr
import System.Environment
import Data.Array.Repa as R hiding ((++))
import qualified Data.Array.Repa.Repr.ForeignPtr as RFP
import Data.Array.Repa.IO.DevIL
main = do
[f] <- getArgs
(RGB v) <- runIL $ readImage f
RFP.computeIntoP (RFP.toForeignPtr v) (rot180 v)
runIL $ writeImage ("flip-"++f) (RGB v)
return ()
rot180 g = backpermute e flop g
where
e@(Z :. x :. y :. _) = extent g
flop (Z :. i :. j :. k) =
(Z :. x - i - 1 :. y - j - 1 :. k)
This is obviously wrong, because the foreign pointer used as a data source is
at the same time
used as destination, so the data gets overwritten before it is used. Does this
mean that I have
to allocate foreign memory buffers on my own? If so, than it feels kind of
painfull to go through
the hassle of allocating foreign pointers, converting between many different
representations and
so on. Am I doing something wrong and if not is there a more painless way of
working with images
and repa in Haskell?
Jan
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