[racket] Drawing a gradient on text

Wow, that's really fast! Thanks for looking into this.

Unfortunately, text-outline seems to garble some glyphs. Am I
doing something wrong? As of commit e12bf33..., the attached code
produces this ... output, which looks more like an impersonation
of my handwriting than a text path:

http://img580.imageshack.us/img580/9038/garbled.jpg

This is on Arch Linux, cairo 1.10.2-2, pango 1.29.4-1.

Even constructing a path of just a single character (such as "r"
or "e" on my system) exhibits this behavior for me.

Let me know if there's anything I can do to help.

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(require slideshow/pict
         racket/draw)

(dc
 (λ (dc x y)
   (define r (new region%))
   (let ([p (new dc-path%)])
     (send p text-outline
           (make-object font% 35 'default)
           "Hello world"
           x y)
     (send r set-path p))
   (send dc set-clipping-region r)
   (send dc set-brush "black" 'solid)
   (send dc draw-rectangle 0 0 500 200))
 500 200)

7 hours ago, Matthew Flatt wrote:
> I guess I've been waiting for a reason to sort out text paths. The
> `dc-path%' class now has a `text-outline' method (as of the latest in
> the git repo).
> 
> At Sun, 25 Dec 2011 00:00:44 -0700, Michael W wrote:
> > Merry Christmas, Racketeers!
> > 
> > Is there an easy way to draw text to a bitmap% with a gradient?
> > 
> > I briefly looked into adding linear-gradient% and
> > radial-gradient% support to slideshow/pict but unfortunately we
> > can't draw text using an arbitrary brush% as the draw-text method
> > of dc% ignores that.
> > 
> > My current trick is to draw the gradient to one bitmap, draw the
> > text to another bitmap, and then draw the first bitmap to a third
> > bitmap while copying the mask of the second. Is there a better
> > way?
> > 
> > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
> > #lang racket
> > (require slideshow/pict
> >          racket/draw)
> > 
> > (define (compose-picts base alpha)
> >   ;; Return a bitmap% with the colors of base but the alpha of alpha.
> >   (define-values (w h)
> >     (values (inexact->exact (ceiling (pict-width base)))
> >             (inexact->exact (ceiling (pict-height base)))))
> >   (define-values (base-bitmap alpha-bitmap final-bitmap)
> >     (values (make-bitmap w h)
> >             (make-bitmap w h)
> >             (make-bitmap w h)))
> >   (define-values (base-dc alpha-dc final-dc)
> >     (apply values (map (λ(bm) (new bitmap-dc% [bitmap bm]))
> >                        (list base-bitmap alpha-bitmap final-bitmap))))
> >   (send base-dc set-smoothing 'aligned)
> >   (draw-pict base base-dc 0 0)
> >   (send alpha-dc set-smoothing 'aligned)
> >   (draw-pict alpha alpha-dc 0 0)
> >   (send final-dc draw-bitmap base-bitmap 0 0 'solid #f alpha-bitmap)
> >   final-bitmap)
> > 
> > ;; The text to render
> > (define my-text
> >   (scale (text "Hello World") 4))
> > 
> > ;; The linear-gradient% to render
> > (define gradient
> >   (new linear-gradient% [x0 0] [y0 0] [x1 0] [y1 (pict-height my-text)]
> >        [stops (list (list 0.0 (make-object color% 0 0 0))
> >                     (list 1.0 (make-object color% 255 0 0)))]))
> > 
> > ;; A box containing the gradient
> > (define gradient-box
> >   (dc
> >    (λ(dc w h)
> >      (send dc set-pen (make-object pen% "white" 1 'transparent))
> >      (send dc set-brush (new brush% [gradient gradient]))
> >      (send dc draw-rectangle
> >            0 0 (pict-width my-text) (pict-height my-text)))
> >    (pict-width my-text) (pict-height my-text)))
> > 
> > ;; The final result: Gradient-filled text!
> > (bitmap (compose-picts gradient-box my-text))
> > 
> > -- 
> > Heave ho,
> >     _mike

-- 
For the Future!
    _mike