wxhaskell-users

[wxhaskell-users] Problem with wxHaskell

[Wojtek M. <wo...@cs...>]

  Hello all,

First of all I would like to say that I think that wxHaskell is a great
library. Do you plan to implement OleAutomation object soon?

However, I have a problem. I've been trying to write a small library on top
of wxHaskell, in order to provide very simple drawing capabilities for
people like me, who do not want or need to know about
all the contexts and so on and want just to draw pictures. So I have created
a simple state monad which threads Window () along with ClientDC(). However,
the attached program doesn't work as expected - when the new rectangle is
drawn, the old one turns black. (the important part of Main.hs is testRect
which actually draws things, rest of stuff in Main.hs just computes the
route and colors. What should I change so that the program won't exhibit
this problem?

Wojtek

Re: [wxhaskell-users] Problem with wxHaskell

[Arjan v. I. <af...@cs...>]

Hi Wojtek,

> when the new rectangle is
> drawn, the old one turns black.

No, it doesn't. Your computer is too fast :-) A colored rectangle is drawn
with a black *border*. Then you draw a new rectangle that is only one pixel
to the left/right and one pixel up/down. All you see of the old rectangle is
its black border. To fix this you can change your setColor function to also
change the pen color (border color) and not only the brush color (fill
color):

setColor :: Color -> SGM ()
setColor c = runDC $ \dc -> do
    dcSetBrushStyle dc (BrushStyle BrushSolid c)
    dcSetPenStyle dc (penColored c 1)

Or you can move your rectangles over a larger distance and then you'll see
that their inside is indeed colored:

dirToVector dir =
  let (x, y) = case dir of
        NW -> (-3, -3)
        NE -> (3, -3)
        SW -> (-3, 3)
        SE -> (3, 3)
     in vector x y


Good luck, Arjan

RE: [wxhaskell-users] Problem with wxHaskell

[Wojtek M. <wo...@cs...>]

> -----Original Message-----
> From: Arjan van IJzendoorn [mailto:af...@cs...]
> Sent: Tuesday, November 11, 2003 6:06 AM
> To: Wojtek Moczydlowski; wxh...@li...
> Subject: Re: [wxhaskell-users] Problem with wxHaskell
>
>
> Hi Wojtek,
>
> > when the new rectangle is
> > drawn, the old one turns black.
>
> No, it doesn't. Your computer is too fast :-) A colored rectangle is drawn

It makes sense and your modification works. Thanks!

But actually, the speed is very slow. When I drew the rectangle just by
calling putPixel on appropriate points, on 2.5 GHz machine, even after
compilation with -O2 switch it worked slowly. I suppose that my old 33 Mhz
machine with a similar program in Pascal would do better. Of course, Haskell
is not fast, but this was way too slow for the computer of these
capabilities. Any ideas what's the reason?

Wojtek

Re: [wxhaskell-users] Problem with wxHaskell

[Arjan v. I. <af...@cs...>]

Hi Wojtek,

> But actually, the speed is very slow. When I drew the rectangle just by
> calling putPixel on appropriate points, on 2.5 GHz machine, even after
> compilation with -O2 switch it worked slowly.

Haskell is fast enough and wxWindows itself, too. I think that calling
wxWindows from Haskell takes a little time, though. And that adds up if you
try to draw hundreds of pixels. I believe there is a faster way by drawing
pixels to a buffer and then displaying that buffer. Anyway, drawing the
rectangles works fine, I think.

Arjan