[racket] question about dc% and scale

Oh, sorry.

Robby

On Thu, May 10, 2012 at 10:04 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
>> >
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