Racket preprocessor for CSS & HTML [unstable]
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css-tools/colors.rkt

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#lang racket/base
(require racket/contract racket/match racket/string)
(require "named-colors.rkt")
(module+ test (require rackunit))
;; Conversion functions between RGB and other color systems.
;; Adaptation of colorsys module in the Python library
;; Original source:
;; http://hg.python.org/cpython/file/2.7/Lib/colorsys.py
;; References:
;; http://en.wikipedia.org/wiki/HLS_color_space
(provide rgb->hsl hsl->rgb
rgb->hex hex->rgb
hsl->hex hex->hsl)
;; this makes things work on exact numbers by default
(define (string->exact str)
(string->number str 10 'number-or-false 'decimal-as-exact))
(define unitval? (real-in 0 1))
(define/contract (real->unitval x)
(real? . -> . unitval?)
(min (max 0 x) 1))
(module+ test
(check-equal? (real->unitval -10) 0)
(check-equal? (real->unitval 10) 1)
(check-equal? (real->unitval 0.5) 0.5))
(define DEGREE_MAX 360)
(define degree? (real-in 0 DEGREE_MAX))
(module+ test
(check-false (degree? -1))
(check-true (degree? 0))
(check-true (degree? 149.23))
(check-true (degree? 255))
(check-false (degree? 361)))
;; like (modulo x 1) but works with floating-point numbers
(define (modulo1 x)
(- x (floor x)))
(define/contract (unitval->byte u)
(unitval? . -> . byte?)
(inexact->exact (floor (* u 255))))
(module+ test
(check-equal? (unitval->byte 0) 0)
(check-equal? (unitval->byte 1) 255))
(define/contract (byte->unitval b)
(byte? . -> . unitval?)
(/ b 255))
(module+ test
(check-equal? (byte->unitval 0) 0)
(check-equal? (byte->unitval 255) 1))
(define (degree-string? x)
(and (string? x) (degree? (string->exact x))))
(define/contract (unitval->degree u)
(unitval? . -> . degree-string?)
(format "~a" (exact->inexact (/ (floor (* u DEGREE_MAX 100)) 100))))
(module+ test
(check-equal? (unitval->degree 0) "0.0")
(check-equal? (unitval->degree 0.5) "180.0")
(check-equal? (unitval->degree 1) "360.0"))
(define (unitval->percentage u)
(format "~a%" (exact->inexact (/ (floor (* u 100 100)) 100))))
(module+ test
(check-true (degree-string? "0"))
(check-true (degree-string? "180"))
(check-true (degree-string? "360"))
(check-false (degree-string? "450"))
(check-false (degree-string? 450))
(check-false (degree-string? "foo")))
(define/contract (degree-string->unitval d)
(degree-string? . -> . unitval?)
(/ (string->exact d) DEGREE_MAX))
(module+ test
(check-equal? (degree-string->unitval "0") 0)
(check-equal? (degree-string->unitval "180") (/ 1 2))
(check-equal? (degree-string->unitval "360") 1))
(define/contract (trim-unitval-sign x)
(string? . -> . string?)
(string-trim x "%" #:left? #f))
(module+ test
(check-equal? (trim-unitval-sign "50") "50")
(check-equal? (trim-unitval-sign "50%") "50")
(check-equal? (trim-unitval-sign "%50%") "%50"))
(define/contract (unitval-string? x)
(any/c . -> . boolean?)
(and (string? x)
(equal? #\% (car (reverse (string->list x))))
((real-in 0 100) (string->exact (trim-unitval-sign x)))))
(module+ test
(check-true (unitval-string? "56%"))
(check-true (unitval-string? "0.00001%"))
(check-false (unitval-string? 50))
(check-false (unitval-string? "50"))
(check-false (unitval-string? "-12%"))
(check-false (unitval-string? "200%")))
(define/contract (unitval-string->unitval x)
(unitval-string? . -> . unitval?)
(/ (string->exact (trim-unitval-sign x)) 100))
(module+ test
(check-equal? (unitval-string->unitval "50%") (/ 1 2))
(check-equal? (unitval-string->unitval "100%") 1)
(check-equal? (unitval-string->unitval "0%") 0))
(define (trim-pound-sign x)
(string-trim x "#" #:right? #f))
(define (make-hex-number x)
(string->exact (string-append "#x" (trim-pound-sign x))))
(define HEX_DIGITS (string->list "0123456789abcdef"))
(define (hex-digit? x)
(member x HEX_DIGITS))
(define (base-hex? x)
(and (string? x)
(equal? (substring x 0 1) "#")
(andmap hex-digit? (string->list (string-downcase (trim-pound-sign x))))))
(define (short-hex? x) ; like #ddd
(and (= (string-length x) 4) (base-hex? x)))
(define (long-hex? x) ; like #e802cf
(and (= (string-length x) 7) (base-hex? x)))
(define (hex? x)
(or (short-hex? x) (long-hex? x)))
(define rgb? (list/c unitval? unitval? unitval?))
(define hsl? rgb?)
(define (rgbish? x)
(ormap (λ(proc) (proc x))
(list
rgb?
(list/c unitval-string? unitval-string? unitval-string?)
(list/c byte? byte? byte?)
hex?
named-color?)))
(define/contract (rgbish->rgb x)
(rgbish? . -> . rgb?)
;; must handle all possible branches of rgbish
(cond
[(rgb? x) x]
[((list/c unitval-string? unitval-string? unitval-string?) x)
(map unitval-string->unitval x)]
[((list/c byte? byte? byte?) x) (map byte->unitval x)]
[(hex? x) (hex->rgb x)]
[(named-color? x) (rgbish->rgb (named-color->hex x))]
[else #f]))
(define (hslish? x)
(ormap (λ(proc) (proc x))
(list
hsl?
(list/c degree-string? unitval-string? unitval-string?) ; aka css-hsl
(list/c byte? byte? byte?))))
(define (hslish->hsl x)
(hslish? . -> . hsl?)
(cond
[(hsl? x) x]
[((list/c degree-string? unitval-string? unitval-string?) x) (cons (degree-string->unitval (car x)) (map unitval-string->unitval (cdr x)))]
[((list/c byte? byte? byte?) x) (map byte->unitval x)]
[else #f]))
(define (hsl->css hsl)
(hslish? . -> . hsl?)
(match-define (list h s lum) (hslish->hsl hsl))
(list (unitval->degree h) (unitval->percentage s) (unitval->percentage lum)))
;; convert rgb values into hue value
(define/contract (rgb->h r g b)
(unitval? unitval? unitval? . -> . unitval?)
(define maxc (max r g b))
(define minc (min r g b))
(if (minc . = . maxc)
0 ; color is gray. Return now & avoid division by zero below
(let ()
(define-values (rc gc bc)
(apply values (map (λ(x) (/ (- maxc x) (- maxc minc))) (list r g b))))
(modulo1 (/ (cond
[(r . = . maxc) (- bc gc)]
[(g . = . maxc) (+ 2.0 (- rc bc))]
[else (+ 4.0 (- gc rc))])
6.0)))))
(define/contract (rgb->hsl rgb)
(rgbish? . -> . hsl?)
(match-define (list r g b) (rgbish->rgb rgb))
(define maxc (max r g b))
(define minc (min r g b))
(define h (rgb->h r g b))
(define lum (/ (+ maxc minc) 2))
(define s (/ (- maxc minc) (if (lum . <= . 0.5)
(+ maxc minc)
(- 2.0 maxc minc))))
(map real->unitval (list h s lum)))
(define/contract (hsl->rgb hsl)
(hslish? . -> . rgb?)
(define ONE_THIRD (/ 1 3))
(define ONE_SIXTH (/ 1 6))
(define TWO_THIRDS (/ 2 3))
(match-define (list h s lum) (hslish->hsl hsl))
(define (_v m1 m2 hue)
(let ([hue (modulo1 hue)])
(cond
[(hue . < . ONE_SIXTH) (+ m1 (* (- m2 m1) hue 6.0))]
[(hue . < . 0.5) m2]
[(hue . < . TWO_THIRDS) (+ m1 (* (- m2 m1) (- TWO_THIRDS hue) 6.0))]
[else m1])))
(define m2 (if (lum . <= . 0.5)
(* lum (+ 1.0 s))
(- (+ lum s) (* lum s))))
(define m1 (- (* 2.0 lum) m2))
(map real->unitval (map (λ(x) (_v m1 m2 x))
(list (+ h ONE_THIRD) h (- h ONE_THIRD)))))
(define/contract (rgb->hex rgb)
(rgbish? . -> . hex?)
;; make a 2-digit hex string from a number
(define (hex-format num)
(define hex (format "~x" num))
(if (= (string-length hex) 1)
(string-append "0" hex)
hex))
(define raw-hex (apply string-append (map hex-format (map unitval->byte (rgbish->rgb rgb)))))
(define triple-double-pattern #px"^(\\w)\\1(\\w)\\2(\\w)\\3$")
(define result (regexp-match triple-double-pattern raw-hex))
(string-append "#" (if result
; cdr result holds the three submatches
(apply string-append (cdr result))
raw-hex)))
(module+ test
(check-equal? (rgb->hex '(1 1 1)) "#fff")
(check-equal? (rgb->hex '(0.8 0.8 0.8)) "#ccc")
(check-equal? (rgb->hex '(0.01 0.01 0.01)) "#020202"))
(define/contract (hex->long-hex hex)
(hex? . -> . long-hex?)
(if (short-hex? hex)
(let ()
(match-define (list d1 d2 d3) (cdr (regexp-match #px"^#(\\w)(\\w)(\\w)$" hex)))
(string-append "#" d1 d1 d2 d2 d3 d3))
hex))
(define/contract (hex->rgb hex)
(hex? . -> . rgb?)
(let ([hex (hex->long-hex hex)])
(define result (regexp-match #px"^#(\\w\\w)(\\w\\w)(\\w\\w)$" hex))
(map (compose1 byte->unitval make-hex-number) (cdr result))))
(define hsl->hex (compose1 rgb->hex hsl->rgb))
(define hex->hsl (compose1 rgb->hsl hex->rgb))