(tty-color-gray-shades): New function.

diff --git a/lisp/term/tty-colors.el b/lisp/term/tty-colors.el
index 8291ac111be2373012cc9b742c33e58bcc16928d..03fef2a34215347869b909707b31cb647fe296d1 100644 (file)
--- a/lisp/term/tty-colors.el
+++ b/lisp/term/tty-colors.el
@@ -956,3 +956,22 @@ NAME is not necessarily the same string as the argument COLOR, because
 the latter might need to be approximated if it is not supported directly."
   (let ((idx (tty-color-translate color frame)))
     (tty-color-by-index idx frame)))
+
+(defun tty-color-gray-shades (&optional display)
+  "Return the number of gray colors supported by DISPLAY's terminal.
+A color is considered gray if the 3 components of its RGB value are equal."
+  (let* ((frame (if (framep display) display
+                 ;; FIXME: this uses an arbitrary frame from DISPLAY!
+                 (car (frames-on-display-list display))))
+        (colors (tty-color-alist frame))
+        (count 0)
+        desc r g b)
+    (while colors
+      (setq desc (cddr (car colors))
+           r (car desc)
+           g (cadr desc)
+           b (car (cddr desc)))
+      (and (eq r g) (eq g b)
+          (setq count (1+ count)))
+      (setq colors (cdr colors)))
+    count))