Re: [wxhaskell-users] Is this PixelBuffer's bug?

[shelarcy <she...@ca...>]

On Fri, 30 Jul 2004 13:40:05 +0200, Daan Leijen <da...@cs...> wrote:
> To make this all clearer, here is a small sample that you can modify
> to implement your filter: (but a version that is based on images
> directly would of course still be  better):
>
>   onPaint vbitmap dc viewArea
>       = do mbBitmap <- varGet vbitmap
>            case mbBitmap of
>              Nothing -> dcClear dc
>              -- Just bm -> drawBitmap dc bm pointZero False []
>              Just bm ->
>                do  sz  <- get bm size
>                    im  <- imageCreateFromBitmap bm
>                    pb  <- imageGetPixelBuffer im
>                    fillPixelBuffer pb sz
>                    bm' <- bitmapCreateFromImage im (-1)
>                    drawBitmap dc bm' pointZero True []
>                    bitmapDelete bm'
>                    imageDelete im
>       where
>         fillPixelBuffer pb bound
>           = mapM_ redshift [Point x y | x <- [0..sizeW bound-1]
>                                       , y <- [0..sizeH bound-1]]
>           where
>             redshift pt
>               = do c <- pixelBufferGetPixel pb pt
> 		   let newcolor = rgb 255 (colorGreen c) (colorBlue c)
>                    pixelBufferSetPixel pb pt newcolor

I chaged the program like this.But program doen't work yet.
Where is my mistake?

     onPaint vbitmap dc viewArea
       = do mbBitmap <- varGet vbitmap
            case mbBitmap of
              Nothing -> dcClear dc
              -- Just bm -> drawBitmap dc bm pointZero False []
              Just bm ->
                do
                    sz <- get bm size
                    im <- imageCreateFromBitmap bm
                    pb <- imageGetPixelBuffer im
                    fillpixelBuffer pb sz
                    bm'  <- bitmapCreateFromImage im (-1)
                    drawBitmap dc bm' pointZero True []
                    bitmapDelete bm'
                    imageDelete im
                    where
                      fillpixelBuffer pb bound =
                        mapM_ drawLowpassFilter [Point x y | x <- [0..sizeW  
bound-1]
                                                           , y <- [0..sizeH  
bound-1]]
                        where
                            drawLowpassFilter (Point szx szy) = do
                                lowpass <- (lowpassFilter (Point szx szy)  
bound)
                                pixelBufferSetPixel pb (Point szx szy)  
lowpass
                            pixelColorInt (Point ptx pty) (Size szx szy)
                                | ptx < 0   = pixelColorInt (Point 0 pty)  
(Size szx szy)
                                | pty < 0   = pixelColorInt (Point ptx 0)  
(Size szx szy)
                                | ptx > szx = pixelColorInt (Point ptx pty)  
(Size 0 szy)
                                | pty < szy = pixelColorInt (Point ptx pty)  
(Size 0 szy)
                                | otherwise = do
                                    pixel <- pixelBufferGetPixel pb (Point  
ptx pty)
                                    return (intFromColor pixel)
                            lowpassFilter (Point szx szy) bound   = do
                                -- pixelsInt <- foldM (+) (pixelColorInt  
[Point x y  | x <- [szx-n..szx+n], y <- [szy-n..szy+n]])
                                pix1 <- pixelColorInt (Point (szx-1)  
(szy-1)) bound
                                pix2 <- pixelColorInt (Point (szx-1) (szy))  
bound
                                pix3 <- pixelColorInt (Point (szx-1)  
(szy+1)) bound
                                pix4 <- pixelColorInt (Point (szx) (szy-1))  
bound
                                pix5 <- pixelColorInt (Point (szx) (szy))  
bound
                                pix6 <- pixelColorInt (Point (szx) (szy+1))  
bound
                                pix7 <- pixelColorInt (Point (szx+1)  
(szy-1)) bound
                                pix8 <- pixelColorInt (Point (szx+1) (szy))  
bound
                                pix9 <- pixelColorInt (Point (szx+1)  
(szy+1)) bound
                                let pixes = (pix1 + pix2 + pix3 + pix4  
+ pix5 + pix6 + pix7 + pix8 + pix9) `div` 9
                                return (colorFromInt  pixes)   --  
(colorFromInt $  (pixelsInt / 9))


> Anyway, here is why your program doesn't work:
> 1) The pixelbuffer returned from "imageGetPixelBuffer" is a static
> pointer to the image data: if you change the pixelbuffer, the image
> changes too!  Therefore, do *not* delete the pixelbuffer.
>
> 2) When the pixelbuffer is changed, the image is changed too -- there
> is no need to create a separate pixelbuffer and image. First read all
> pixels into list of something, and than write them back again when
> they are changed according to your filter.
>
> 3) You delete the original bitmap in the paint handler... the next time
> it is called the data is invalid.
>
> 4) It would be much better to store the image only in the "vbitmap" and
> not a bitmap. That way, you only need to manipulate the image once (and
> not at every call to "onPaint", and you only extract a bitmap from an  
> image.
>
> 5) You indices are out-of-bounds. The range is from 0 to the width,
> instead of 0 to the width-1.


PS.

> ps. Are you from Japan? As a Dutchman, I have always been interested
> in Japan -- would love to go there some time and snowboard on Mt. Fuji  
> :-)

Yes. I am Japanese. Shelarcy is handle and nick name.
I'm glad to you are interested in Japan.



-- 
shelarcy <she...@ca...>
http://page.freett.com/shelarcy/