How to convert decimal to hexadecimal in Scheme? (Need to convert RGB to HEX in GIMP)

Question

How to convert decimal to hexadecimal in Scheme?

Need to convert RGB to HEX in GIMP for JSON after:

(set! imgcolor (car (gimp-color-picker image newDraw 1 1 TRUE TRUE 1)))

in Script-fu. Result now is in RGB like: (255 255 255)

Answer 1

Find answer in pallete-export.scm Written by Barak Itkin

; For all the operations below, this is the order of respectable digits:
(define conversion-digits (list "0" "1" "2" "3" "4" "5" "6" "7" "8" "9"
                                "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k"
                "l" "m" "n" "o" "p" "q" "r" "s" "t" "u" "v"
                "w" "x" "y" "z"))


; Converts a decimal number to another base. The returned number is a string
(define (convert-decimal-to-base num base)
  (if (< num base) 
    (list-ref conversion-digits num) 
    (let loop ((val num)
               (order (inexact->exact (truncate (/ (log num) 
                                                   (log base)))))
               (result ""))
      (let* ((power (expt base order))
             (digit (quotient val power)))
        (if (zero? order)
          (string-append result (list-ref conversion-digits digit)) 
          (loop (- val (* digit power))
                (pred order)
                (string-append result (list-ref conversion-digits digit))))))))


; Convert a color to a hexadecimal string
; '(255 255 255) => "#ffffff"
(define (color-rgb-to-hexa-decimal color)
  (string-append "#"
                 (pre-pad-number
          (convert-decimal-to-base (car color) 16) 2 "0")
                 (pre-pad-number
          (convert-decimal-to-base (cadr color) 16) 2 "0")
                 (pre-pad-number
          (convert-decimal-to-base (caddr color) 16) 2 "0")
                 )
  )

; Присваеваем HEX переменной 
(set! imgcolorHEX (color-rgb-to-hexa-decimal imgcolor))