text: Use pixel width for centering

* text-conf.el (center-string-in-width, make-block): Use the function
  `string-pixel-width` to calculate the correct widths of strings, in
  centering the strings.

1 files changed, 50 insertions, 7 deletions

diff --git a/text-conf.el b/text-conf.el
index c8bc566..bd2ebaf 100644
--- a/text-conf.el
+++ b/text-conf.el
@@ -47,7 +47,7 @@ exactly the current ilne."
         (setq index (1+ index)))
       (insert remainder-string))))
 
-;;; Center text
+;;; Make a centered string
 
 ;;;###autoload
 (defun correct-length (str)
@@ -75,14 +75,57 @@ Characters that take up more than one column will be counted with
 (defun center-string-in-width (str width)
   "Add spaces to STR so that it is centered in a box which is WIDTH \
 wide."
-  (let ((len (string-width str)))
+  (let* ((space-width (string-pixel-width (string 32)))
+         (width (* width space-width))
+         (len (string-pixel-width str)))
     (cond
      ((> len width)
       (error "String %s longer than %d" str width))
-     (t (format "%s%s"
-                (make-string (round (- width len) 2)
-                             32)
-                str)))))
+     (t (concat
+         (make-string
+          (round  (- width len) (* space-width 2))
+          32)
+         str)))))
+
+;;; Center the string
+
+(defun make-center-line (&optional nlines)
+  "Center the line point is on, within the width specified by
+`fill-column'.
+
+This means adjusting the indentation so that it equals the
+distance between the end of the text and `fill-column'.  The
+argument NLINES says how many lines to center.
+
+This is adapted from the function `center-line' by Durand at
+2024-02-20 23:27:43.839601."
+  (interactive "P")
+  (if nlines (setq nlines (prefix-numeric-value nlines)))
+  (while (not (eq nlines 0))
+    (save-excursion
+      (let ((lm (current-left-margin))
+            space)
+	(beginning-of-line)
+	(delete-horizontal-space)
+	(end-of-line)
+	(delete-horizontal-space)
+        (setq space (- fill-column
+                       lm
+                       (round
+                        (car
+                         (window-text-pixel-size
+                          nil (pos-bol) (point)))
+                        (string-pixel-width (string 32)))))
+        (if (> space 0)
+            (indent-line-to (+ lm (/ space 2))))))
+    (cond ((null nlines)
+	   (setq nlines 0))
+	  ((> nlines 0)
+	   (setq nlines (1- nlines))
+	   (forward-line 1))
+	  ((< nlines 0)
+	   (setq nlines (1+ nlines))
+	   (forward-line -1)))))
 
 ;;; Make a block
 
@@ -121,7 +164,7 @@ DESCRIPTION above the block."
     (save-excursion
       (goto-char beg)
       (while (<= (point) (1- (marker-position end-marker)))
-        (center-line)
+        (make-center-line)
         (forward-line 1))
       (goto-char beg)
       (mapc #'insert header)