From f12fca91b185cbf83fbe173fadf6a46f6c3c0c65 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@lysator.liu.se>
Date: Mon, 17 Aug 2020 18:39:53 +0200
Subject: Fixes.

---
 module/util/color.scm | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 module/util/color.scm

(limited to 'module/util/color.scm')

diff --git a/module/util/color.scm b/module/util/color.scm
new file mode 100644
index 00000000..7b6dacec
--- /dev/null
+++ b/module/util/color.scm
@@ -0,0 +1,22 @@
+(define-module (util color)
+  )
+
+;; 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"
+      )))
-- 
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