I don't think such a procedure can be written. at least not for the general
case.
First, the color of `(filled-rectangle 30 30)` is not black, but whatever
color was installed in the drawing context when the filled rectangle was
rendered. You can change it to red using:
(colorize (filled-rectangle 20 20) "red")
Even if you could inspect the colorize pict, it would still not be
sufficient for a general `get-color` function. Users can write their own
pict constructors using dc:
(define colors (list "red" "green" "blue" "yellow"))
(define (my-red-colorize other-pict)
(dc (lambda (dc dx dy)
(define color (list-ref colors (random (length colors))))
(define old-pen (send dc get-pen))
(send dc set-pen (new pen% [width 1] [color color]))
(draw-pict other-pict dc dx dy)
(send dc set-pen old-pen))
(pict-width other-pict)
(pict-height other-pict)))
And a call like `(my-red-colorize (filled-rectangle 20 20))` will only
result in a red rectangle about 25% of the time.
Even if you want to ignore cases like the above, what should `get-color`
return for the picture below?
(hc-append (colorize (filled-rectangle 20 20) "red") (colorize
(filled-rectangle
20 20) "blue"))
Alex.
On Saturday, April 18, 2020 at 8:00:12 PM UTC+8, Raoul Schorer wrote:
>
> Hi,
>
> Using the 'pict' library, I could not find predicates regarding color in
> the doc.
> Is there something like
>
> (get-color (filled-rectangle 30 30)) --> "black"
>
> somewhere?
> If not, how can I make a reliable color predicate?
>
> Thanks,
> Raoul
>
--
You received this message because you are subscribed to the Google Groups
"Racket Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to racket-users+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/racket-users/d3fa9021-63af-4129-bfb6-a82e219cfcf0%40googlegroups.com.
