[racket] question about dc% and scale

Okay, yes, using a dc-path% seems to work as intended.

Thanks!

-- Garrett Mitchener

On Thu, May 10, 2012 at 11:04 AM, Matthew Flatt <mflatt at cs.utah.edu> wrote:

> Although pixel alignment can be confusing, I think this one is just a
> bug.
>
> The `draw-rectangle' method tries to adjust the width of an outline so
> that in the simple case --- a width 0 or 1 pen in unsmoothed or aligned
> mode with a bitmap target --- the rectangle outline is the given width
> and height, instead of extending an extra pixel. That adjustment isn't
> implemented correctly, and the problem is particularly clear with a
> large scaling factor.
>
> You can work around the problem by creating a rectangle `dc-path%' and
> drawing it with `draw-path'. Meanwhile, I'll fix `draw-rectangle'.
>
> At Thu, 10 May 2012 09:57:26 -0500, Robby Findler wrote:
> > The problem is that the coordinates are "between" the pixels. There is an
> > explanation of this in the context of another library, but the issues are
> > the same:
> >
> >
> >
> http://docs.racket-lang.org/teachpack/2htdpimage.html?q=2htdp/image#%28part._nitty-g
> > ritty%29
> >
> > hth,
> > Robby
> >
> > On Thu, May 10, 2012 at 8:29 AM, Garrett Mitchener <
> > garrett.mitchener at gmail.com> wrote:
> >
> > > Hi, I'm learning the racket GUI package, and I ran into something that
> > > doesn't make sense to me:
> > >
> > > #lang racket/gui
> > >
> > > (define black-pen
> > >   (new pen%
> > >        [width 1]
> > >        [color "black"]))
> > >
> > > (define blue-brush
> > >   (new brush%
> > >        [color "blue"]))
> > >
> > > (define (draw-test-2 dc)
> > >   (send dc scale 10 10)
> > >   (send dc set-pen black-pen)
> > >   (send dc set-brush blue-brush)
> > >   (send dc draw-rectangle 7 2 4 4))
> > >
> > > (define pic (make-bitmap 200 100))
> > >
> > > (define dc (new bitmap-dc% [bitmap pic]))
> > >
> > > (draw-test-2 dc)
> > >
> > > And at the end, pic looks like this:
> > >
> > > [image: Inline image 1]
> > > The outline and the filling don't line up.  What am I doing wrong?
>  This
> > > is with DrRacket 5.2.1 on linux.
> > >
> > > Thanks,
> > > -- Garrett Mitchener
> > >
> > > ____________________
> > >  Racket Users list:
> > >  http://lists.racket-lang.org/users
> > >
> > >
> > ____________________
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> >   http://lists.racket-lang.org/users
>
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