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

[Daan L. <da...@cs...>]

shelarcy wrote:

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

Hi Shelarcy,

Your mistakes are in the plain Haskell code. For example:

> 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 

If I call this with (Point x y) (Size sz sy) where y < sy,
this function loops indefinitely. What you should try to do
is to split up everything into small functions that can be
tested independently -- instead of writing everything at once.
Also, if certain expression patterns occur more than once, try
to make that into a function.

Anyway, to help you along, I have attached a version of your
program that does what you want. As you will notice, it is
rather slow. After some testing I found that it is due to the
slow "pixelBufferGet/SetPixel" functions. In the cvs release
I'll commit a version that allows you to retrieve the entire
buffer at once which makes it much faster. That version is
probably available by anonymous cvs tomorrow.

All the best,
 Daan.