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Diffstat (limited to '')
-rw-r--r-- | module/calp/html/util.scm | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/module/calp/html/util.scm b/module/calp/html/util.scm index ecb54198..75137d4e 100644 --- a/module/calp/html/util.scm +++ b/module/calp/html/util.scm @@ -13,3 +13,23 @@ (lambda (ev) (or (id ev) (set/r! (id ev) (symbol->string (gensym "__html_id_"))))))) + +;; Returns a color with good contrast to the given background color. +;; https://stackoverflow.com/questions/1855884/determine-font-color-based-on-background-color/1855903#1855903 +(define-public (calculate-fg-color c) + (catch #t + (lambda () + (define (str->num c n) (string->number (substring/shared c n (+ n 2)) 16)) + ;; (format (current-error-port) "COLOR = ~s~%" c) + (let ((r (str->num c 1)) + (g (str->num c 3)) + (b (str->num c 5))) + (if (< 1/2 (/ (+ (* 0.299 r) + (* 0.587 g) + (* 0.114 b)) + #xFF)) + "#000000" "#FFFFFF"))) + (lambda args + (format (current-error-port) "Error calculating foreground color?~%~s~%" args) + "#FF0000" + ))) |