qwerthjkdfghjk.el

;; Bryan Maass
;; blending adding subtracting colors in elisp
(defun red   (rgb) (car rgb))
(defun green (rgb) (cadr rgb))
(defun blue  (rgb) (caddr rgb))

(defun color->rgb (c)
  (let ((step (if (= 7 (length c)) 2 1)))
    (list (string-to-number (substring c 1                (+ 1 step))       16)
          (string-to-number (substring c (+ 1 step)       (+ 1 (* 2 step))) 16)
          (string-to-number (substring c (+ 1 (* 2 step)) (+ 1 (* 3 step))) 16))))

(defun rgb->color (rgb)
  (concat "#"
          (format "%02x" (red rgb))
          (format "%02x" (green rgb))
          (format "%02x" (blue rgb))))

(defun int->hex-str (n)
  (cond
   ((> n 255) "FF")
   ((< n 0)   "00")
   (t         (format "%02x" n))))

(defun color-fn (c1 c2 fn)
  (let ((rgb1 (color->rgb c1))
        (rgb2 (color->rgb c2)))
    (rgb->color
     (list (funcall fn (red rgb1) (red rgb2))
           (funcall fn (green rgb1) (green rgb2))
           (funcall fn (blue rgb1)  (blue rgb2))))))

(defun color-add (c1 c2)
  (color-fn c1 c2 (lambda (a b) (min 255 (+ a b)))))

(defun blend (c1 c2)
  (color-fn c1 c2 (lambda (a b) (min 255 (max 0 (/ (+ a b) 2))))))

(defun color-minus (c1 c2)
  (color-fn c1 c2 (lambda (a b) (max 0 (- a b)))))

(defun lighten (c) (color-add c "#111111"))
(defun darken  (c) (color-minus c "#111111"))