;; with a large scroll bar portion can easily overflow a lisp int.
(truncate (/ (* (float (car num-denom)) whole) (cdr num-denom))))
+(defun scroll-bar-columns (side)
+ "Return the width, measured in columns, of the vertical scrollbar on SIDE.
+SIDE must be the symbol `left' or `right'."
+ (let* ((wsb (window-scroll-bars))
+ (vtype (nth 2 wsb))
+ (cols (nth 1 wsb)))
+ (cond
+ ((not (memq side '(left right)))
+ (error "`left' or `right' expected instead of %S" side))
+ ((and (eq vtype side) cols))
+ ((eq (frame-parameter nil 'vertical-scroll-bars) side)
+ ;; nil means it's a non-toolkit scroll bar, and its width in
+ ;; columns is 14 pixels rounded up.
+ (ceiling (or (frame-parameter nil 'scroll-bar-width) 14)
+ (frame-char-width)))
+ (0))))
+
\f
;;;; Helpful functions for enabling and disabling scroll bars.