Hello,
I am attempting to process images captured from a webcam. My aim is to
do so, in real time, at the frame rate of the camera. I'm using GHC
6.4.2 with -O3.
A frame consists of ~100k 24bit colour values.
The webcam is interfaced through FFI bindings to some C++ -- these are
all labelled 'unsafe'. The image is passed to Haskell as a Ptr Word8.
To blit this to the screen (via Gtk2Hs) I do the following:
data Cam = Cam { snap_width :: !Int
, snap_height :: !Int
, snap_bytespp :: !Int
, snap_size :: !Int
, cam_img :: Ptr Word8
, cam_obj :: ForeignPtr ()
}
do (PixbufData _ dst _) <- (pixbufGetPixels pixbuf :: IO (PixbufData Int Word8))
copyBytes dst (cam_img cam)
This achieves the desired throughput (25-29fps.) However, I am at a
bit of a loss how to do something similar for preprocessing the data
in Haskell before blitting the data (whilst also retaining some
semblance of functional programming...)
Currently, I have:
cam_snap cam f x
= do let loop (r:g:b:rest) n x = f r g b n x >>= loop rest (n+3)
loop _ _ x = return x
px <- peekArray (snap_size cam) (cam_img cam)
loop px 0 x
cam_snap2 cam f x
= let loop ptr n x
| n >= snap_size cam
= return x
| otherwise
= do let ptrs = scanl plusPtr ptr [1,1]
[r,g,b] <- mapM peek ptrs
f r g b n x >>= loop (ptr `plusPtr` 3) (n+3)
in loop (cam_img cam) 0 x
do ...
let sum_px r g b _ (sr,sg,sb) = return (sr+r,sg+g,sb+b)
sum <- cam_snap (cam ui) sum_px (0.0,0.0,0.0)
print sum
cam_snap only processes at 5 fps, whereas cam_snap2 operates at 6fps.
Any suggestions?
Thanks.
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