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(in-package :cl-colors)
;;; color representations
(deftype unit-real ()
"Real number in [0,1]."
'(real 0 1))
(defstruct (rgb (:constructor rgb (red green blue)))
"RGB color."
(red nil :type unit-real :read-only t)
(green nil :type unit-real :read-only t)
(blue nil :type unit-real :read-only t))
(defmethod make-load-form ((p rgb) &optional env)
(declare (ignore env))
(make-load-form-saving-slots p))
(defun gray (value)
"Create an RGB representation of a gray color (value in [0,1)."
(rgb value value value))
(define-structure-let+ (rgb) red green blue)
(defstruct (hsv (:constructor hsv (hue saturation value)))
"HSV color."
(hue nil :type (real 0 360) :read-only t)
(saturation nil :type unit-real :read-only t)
(value nil :type unit-real :read-only t))
(defmethod make-load-form ((p hsv) &optional env)
(declare (ignore env))
(make-load-form-saving-slots p))
(define-structure-let+ (hsv) hue saturation value)
(defun normalize-hue (hue)
"Normalize hue to the interval [0,360)."
(mod hue 360))
;;; conversions
(defun rgb-to-hsv (rgb &optional (undefined-hue 0))
"Convert RGB to HSV representation. When hue is undefined (saturation is
zero), UNDEFINED-HUE will be assigned."
(let+ (((&rgb red green blue) rgb)
(value (max red green blue))
(delta (- value (min red green blue)))
(saturation (if (plusp value)
(/ delta value)
((&flet normalize (constant right left)
(let ((hue (+ constant (/ (* 60 (- right left)) delta))))
(if (minusp hue)
(+ hue 360)
(hsv (cond
((zerop saturation) undefined-hue) ; undefined
((= red value) (normalize 0 green blue)) ; dominant red
((= green value) (normalize 120 blue red)) ; dominant green
(t (normalize 240 red green)))
(defun hsv-to-rgb (hsv)
"Convert HSV to RGB representation. When SATURATION is zero, HUE is
(let+ (((&hsv hue saturation value) hsv))
;; if saturation=0, color is on the gray line
(when (zerop saturation)
(return-from hsv-to-rgb (gray value)))
;; nonzero saturation: normalize hue to [0,6)
(let+ ((h (/ (normalize-hue hue) 60))
((&values quotient remainder) (floor h))
(p (* value (- 1 saturation)))
(q (* value (- 1 (* saturation remainder))))
(r (* value (- 1 (* saturation (- 1 remainder)))))
((&values red green blue) (case quotient
(0 (values value r p))
(1 (values q value p))
(2 (values p value r))
(3 (values p q value))
(4 (values r p value))
(t (values value p q)))))
(rgb red green blue))))
(defun hex-to-rgb (string)
"Parse hexadecimal notation (eg ff0000 or f00 for red) into an RGB color."
(let+ (((&values width max)
(case (length string)
(3 (values 1 15))
(6 (values 2 255))
(t (error "string ~A doesn't have length 3 or 6, can't parse as ~
RGB specification" string))))
((&flet parse (index)
(/ (parse-integer string :start (* index width)
:end (* (1+ index) width)
:radix 16)
(rgb (parse 0) (parse 1) (parse 2))))
;;; conversion with generic functions
(defgeneric as-hsv (color &optional undefined-hue)
(:method ((color rgb) &optional (undefined-hue 0))
(rgb-to-hsv color undefined-hue))
(:method ((color hsv) &optional undefined-hue)
(declare (ignore undefined-hue))
(defgeneric as-rgb (color)
(:method ((rgb rgb))
(:method ((hsv hsv))
(hsv-to-rgb hsv))
(:method ((string string))
;; TODO in the long run this should recognize color names too
(hex-to-rgb string)))
;;; combinations
;;; internal functions
(declaim (inline cc))
(defun cc (a b alpha)
"Convex combination (1-ALPHA)*A+ALPHA*B, ie ALPHA is the weight of A."
(declare (type (real 0 1) alpha))
(+ (* (- 1 alpha) a) (* alpha b)))
(defun rgb-combination (color1 color2 alpha)
"Color combination in RGB space."
(let+ (((&rgb red1 green1 blue1) (as-rgb color1))
((&rgb red2 green2 blue2) (as-rgb color2))
((&flet c (c1 c2) (cc c1 c2 alpha))))
(rgb (c red1 red2)
(c green1 green2)
(c blue1 blue2))))
(defun hsv-combination (hsv1 hsv2 alpha &optional (positive? t))
"Color combination in HSV space. POSITIVE? determines whether the hue
combination is in the positive or negative direction on the color wheel."
(let+ (((&hsv hue1 saturation1 value1) (as-hsv hsv1))
((&hsv hue2 saturation2 value2) (as-hsv hsv2))
((&flet c (c1 c2) (cc c1 c2 alpha))))
(hsv (cond
((and positive? (> hue1 hue2))
(normalize-hue (c hue1 (+ hue2 360))))
((and (not positive?) (< hue1 hue2))
(normalize-hue (c (+ hue1 360) hue2)))
(t (c hue1 hue2)))
(c saturation1 saturation2)
(c value1 value2))))
;;; macros used by the autogenerated files
(defmacro define-rgb-color (name red green blue)
"Macro for defining color constants. Used by the automatically generated color file."
(let ((constant-name (symbolicate #\+ name #\+)))
(define-constant ,constant-name (rgb ,red ,green ,blue)
:test #'equalp :documentation ,(format nil "X11 color ~A." name)))))