module Snapshot (hSnapshot, writeSnapshot, snapshotWith) where

import Control.Monad(forM_)
import System.IO(Handle())
import Graphics.Rendering.OpenGL(
  readPixels,
  Position,
  Size(Size),
  PixelData(PixelData),
  PixelFormat(RGB),
  DataType(UnsignedByte))
import Foreign.Marshal.Alloc(allocaBytes)
import Foreign.Ptr(plusPtr)
import qualified Data.ByteString.Internal as BSI
import qualified Data.ByteString as BS

-- save a screenshot as binary PPM
snapshotWith :: (BS.ByteString -> IO b) -> Position -> Size -> IO b
snapshotWith f p0 vp@(Size vw vh) = do
  let fi q = fromIntegral q
      p6 = "P6\n" ++ show vw ++ " " ++ show vh ++ " 255\n"
  allocaBytes (fi (vw*vh*3)) $ \ptr -> do
    readPixels p0 vp $ PixelData RGB UnsignedByte ptr
    px <- BSI.create (fi $ vw * vh * 3) $ \d -> forM_ [0..vh-1] $ \y ->
      BSI.memcpy
        (d`plusPtr`fi(y*vw*3))
        (ptr`plusPtr`fi ((vh-1-y)*vw*3))
        (fi(vw*3))
    f $ BS.pack (map (toEnum . fromEnum) p6) `BS.append` px

hSnapshot :: Handle -> Position -> Size -> IO ()
hSnapshot h = snapshotWith (BS.hPutStr h)

writeSnapshot :: FilePath -> Position -> Size -> IO ()
writeSnapshot f = snapshotWith (BS.writeFile f)