[racket] Fwd: Transformations and hc-append

I'm not sure I can give you more than just hints (and certainly not a
specification) but probably the difference is that pict->bitmap is drawing
the pict at (0,0) in the DC and scribble is drawing it at some random
place. But yeah, I'm sorry, that's still just a guess.

And the examples at that link are really fantastic!

Robby



On Tue, Feb 11, 2014 at 1:03 PM, Jens Axel Søgaard <jensaxel at soegaard.net>wrote:

> 2014-02-11 19:39 GMT+01:00 Robby Findler <robby at eecs.northwestern.edu>:
> > Is the problem that you need to use (more) absolute coordinates in the
> > coordinate arguments to linear-gradient% (either that or set the origin
> of
> > the dc, in the case that you wanted to create the brush only once)?
>
> The problem is that it is unspecified (as far as I know) whether brushes
> used in picts are specified using absolute or relative coordinates. For
> solid
> brushes this makes no difference. For non-solid brushes (gradients and
> textures) there is a choice to be made. I got surprised by the
> behavior and thought
> of it as a bug (I was looking for one - I have an example where a pict
> shows up perfectly in DrRacket but renders differently in Scribble).
>
> If I in shady make a new gradient each time the pict is to be drawn, I get
> the
> behavior I want:
>
>                            (new linear-gradient%
>                                 [x0 x] [y0 y] [x1 (+ x (* 2 r))] [y1
> y] ; horizontal gradient
>                                 [stops (list (list 0   red)   ; (0,0)
> to ( r,0) red->green
>                                              (list 1/2 green) ; (r,0)
> to (2r,0) green->blue
>                                              (list 1   blue))])
>
> Since the pict constructors such as filled-rectangle use the pen, there
> were no way to figure out what was intended.
>
> The last example here: shows that Scribble converts p and (pict->bitmap p)
> differently. I am still puzzled by this.
>
>
> http://soegaard.github.io/docs/metapict/metapict.html#%28part._example-rgb-triangle%29
>
> /Jens Axel
>
>
> > On Tue, Feb 11, 2014 at 10:49 AM, Jens Axel Søgaard <
> jensaxel at soegaard.net>
> > wrote:
> >>
> >> The intent of hc-append is that (hc-append p1 p2) draws p1 and p2
> >> beside each other.
> >>
> >> The question is whether (hc-append p p) should draw to identical picts?
> >>
> >> When I use a non-solid brush I get the two ps are drawn differently.
> >> In (hc-append p1 p2) I was expecting a transformation (translation) on
> >> the brush.
> >>
> >> As a demonstration I offer the following program (a bit long, but
> >> hopefully clear.
> >>
> >> See a syntax-highligthed version here: http://pasterack.org/pastes/7953
> >> The DrRacket output is here: http://imgur.com/5BRiY0Z
> >>
> >> /Jens Axel
> >>
> >>
> >> #lang racket
> >> (require pict)
> >>
> >> ; debug : value pict -> pict
> >> ;  return a pict, that when drawn prints the
> >> ;  brush and drawing context transformation
> >> (define (debug who pict)
> >>   (dc (lambda (dc x y)
> >>         (define b   (send dc get-brush))
> >>         (define bt  (send b  get-transformation))
> >>         (define dct (send dc get-transformation))
> >>         (displayln (list who 'x x 'y y 'brush: bt 'dc: dct))
> >>         (draw-pict pict dc x y))
> >>       (pict-width pict) (pict-height pict)))
> >>
> >> (define r 20) ; use same box side for the entire example
> >>
> >> ; a black filled rectangle
> >> (define (rect) (filled-rectangle r r))
> >>
> >> ;;; Examine whether hc-append does any transformation.
> >> "Expected Image:          Two squares a black and a red"
> >> "Expected Transformation: Same for A and B. Some difference for C."
> >> (debug 'A
> >>        (hc-append (debug 'B (rect))
> >>                   (debug 'C (colorize (rect) "red" ))))
> >>
> >> ;;; --------------------------------------------------------------
> >> (require racket/draw)
> >>
> >> ; colors
> >> (define (color: name) (send the-color-database find-color name))
> >> (define red   (color: "red"))
> >> (define green (color: "green"))
> >> (define blue  (color: "blue"))
> >>
> >> ; square-path : real real real real -> path%
> >> ;     make square with side r and upper left corner (x,y)
> >> (define (square-path x y w h)
> >>   (define p (new dc-path%))
> >>   (send p move-to    x      y)
> >>   (send p line-to    x   (+ y h))
> >>   (send p line-to (+ x w)(+ y h))
> >>   (send p line-to (+ x w)(+ y 0))
> >>   (send p line-to (+ x 0)(+ y 0))
> >>   p)
> >>
> >> ; fill : pict -> pict
> >> ;   draw a path around pict using current pen and brush
> >> (define (fill pict)
> >>   (define w (pict-width pict))
> >>   (define h (pict-height pict))
> >>   (dc (lambda (dc x y)
> >>         (draw-pict pict dc x y)
> >>         (send dc draw-path (square-path x y w h)))
> >>       w h))
> >>
> >> ; shady : pict -> pict
> >> ;   Draws pict with a brush given by a linear, horizontal
> >> ;   gradient from (0,0) to (0,2r). The colors are red->green->blue.
> >> (define (shady pict)
> >>   (dc (lambda (dc x y)
> >>         ; get old brush
> >>         (define b (send dc get-brush))
> >>         ; make new brush, only change gradient
> >>         (define new-brush
> >>           (new brush%
> >>                [color          (send b get-color)]
> >>                [style          (send b get-style)]
> >>                [stipple        (send b get-stipple)]
> >>                [gradient       (new linear-gradient%
> >>                                 [x0 0] [y0 0] [x1 (* 2 r)] [y1 0] ;
> >> horizontal gradient
> >>                                 [stops (list (list 0   red)   ; (0,0)
> >> to ( r,0) red->green
> >>                                              (list 1/2 green) ; (r,0)
> >> to (2r,0) green->blue
> >>                                              (list 1   blue))])]
> >>                [transformation (send b get-transformation)]))
> >>         ; use new brush to draw the pict
> >>         (send dc set-brush new-brush)
> >>         (draw-pict pict dc x y)
> >>         ; restore old brush
> >>         (send dc set-brush b))
> >>       (pict-width pict) (pict-height pict)))
> >>
> >> (define-syntax (echo stx) (syntax-case stx () [(_ expr) #'(values 'expr
> >> expr)]))
> >>
> >> (newline) (newline)
> >> "Expected: A (black) rectangle"
> >> (echo (rect))
> >> "Expected: A rectangle filled with nothing (default brush is empty)"
> >> (echo (fill (rect)))
> >> "Expected: A rectangle filled with linear gradient (red to green)"
> >> (echo (shady (fill (rect))))
> >> "Expected: Two red-to-green rectangles"
> >> (echo (hc-append (shady (fill (rect))) (shady (fill (rect)))))
> >> "Expected: Two red-to-green rectangles"
> >> (echo (let () (define p (shady (fill (rect)))) (hc-append p p)))
> >>
> >>
> >>
> >> --
> >> Jens Axel Søgaard
> >>
> >> ____________________
> >>   Racket Users list:
> >>   http://lists.racket-lang.org/users
> >
> >
>
>
>
> --
> --
> Jens Axel Søgaard
>
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