I basically agree with Alex, as the internal structures of pict don't really keep information in that way, but a "best effort" might be to draw it into a bitmap and then use the bitmap to find the average color or the most common color (perhaps with some error bounds on what colors count as "the same") or something like that.
Robby On Sat, Apr 18, 2020 at 6:49 PM Alex Harsanyi <alexharsa...@gmail.com> wrote: > > > 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. -- 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/CAL3TdONPB16S1srT1%3Dz0ZPM52%3DZh624hrq5zOc7C4oerXqgaCA%40mail.gmail.com.
