Use updated modus-themes formula for contrast tables

I made this change in commit b410fcc in the modus-themes repo. The
idea is to avoid the use of the cl-loop and other cl- functions that
we don't really need.

1 files changed, 15 insertions, 8 deletions

diff --git a/contrast-ratios.org b/contrast-ratios.org
index 6fe30c5..b56aea0 100644
--- a/contrast-ratios.org
+++ b/contrast-ratios.org
@@ -7,20 +7,27 @@ Check this files Git history for updates.
 Evaluate these snippets, otherwise the tables will not work.  Then
 update a table by typing =C-c C-c= with point at the =#+TBLFM:= line.
 
-#+begin_src emacs-lisp
+#+begin_src emacs-lisp :results output silent
 ;; Copied from my `modus-themes'.
 
 ;; This is the WCAG formula to measure relative luminance:
 ;; <https://www.w3.org/TR/WCAG20-TECHS/G18.html>.
+(defun modus-themes--wcag-contribution (channel weight)
+  "Return the CHANNEL contribution to overall luminance given WEIGHT."
+  (* weight
+     (if (<= channel 0.03928)
+         (/ channel 12.92)
+       (expt (/ (+ channel 0.055) 1.055) 2.4))))
+
 (defun modus-themes-wcag-formula (hex)
   "Get WCAG value of color value HEX.
-The value is defined in hexadecimal RGB notation, such as those in
-`modus-themes-operandi-colors' and `modus-themes-vivendi-colors'."
-  (cl-loop for k in '(0.2126 0.7152 0.0722)
-           for x in (color-name-to-rgb hex)
-           sum (* k (if (<= x 0.03928)
-                        (/ x 12.92)
-                      (expt (/ (+ x 0.055) 1.055) 2.4)))))
+The value is defined in hexadecimal RGB notation, such #123456."
+  (let ((channels (color-name-to-rgb hex))
+        (weights '(0.2126 0.7152 0.0722))
+        contribution)
+    (while channels
+      (push (modus-themes--wcag-contribution (pop channels) (pop weights)) contribution))
+    (apply #'+ contribution)))
 
 ;;;###autoload
 (defun modus-themes-contrast (c1 c2)