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.mitche...@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 > > > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
