1 files changed, 52 insertions, 0 deletions
diff --git a/lisp/window.el b/lisp/window.el
index dc33eb8a12a..bb4d51da5f5 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -10480,6 +10480,58 @@ displaying that processes's buffer."
 (put 'shrink-window-horizontally 'repeat-map 'resize-window-repeat-map)
 (put 'shrink-window 'repeat-map 'resize-window-repeat-map)
 
+(defun window-char-pixel-width (&optional window face)
+  "Return average character width for the font of FACE used in WINDOW.
+WINDOW must be a live window and defaults to the selected one.
+
+If FACE is nil or omitted, the default face is used.  If FACE is
+remapped (see `face-remapping-alist'), the function returns the
+information for the remapped face."
+  (with-selected-window (window-normalize-window window t)
+    (let* ((face (if face face 'default))
+	   (info (font-info (face-font face)))
+	   (width (aref info 11)))
+      (if (> width 0)
+	  width
+	(aref info 10)))))
+
+(defun window-char-pixel-height (&optional window face)
+  "Return character height for the font of FACE used in WINDOW.
+WINDOW must be a live window and defaults to the selected one.
+
+If FACE is nil or omitted, the default face is used.  If FACE is
+remapped (see `face-remapping-alist'), the function returns the
+information for the remapped face."
+  (with-selected-window (window-normalize-window window t)
+    (let* ((face (if face face 'default))
+	   (info (font-info (face-font face))))
+      (aref info 3))))
+
+(defun window-max-characters-per-line (&optional window face)
+  "Return the number of characters that can be displayed on one line in WINDOW.
+WINDOW must be a live window and defaults to the selected one.
+
+The character width of FACE is used for the calculation.  If FACE
+is nil or omitted, the default face is used.  If FACE is
+remapped (see `face-remapping-alist'), the function uses the
+remapped face.
+
+This function is different from `window-body-width' in two
+ways.  First, it accounts for the portions of the line reserved
+for the continuation glyph.  Second, it accounts for the size of
+the font, which may have been adjusted, e.g., using
+`text-scale-increase')."
+  (with-selected-window (window-normalize-window window t)
+    (let* ((window-width (window-body-width window t))
+           (font-width (window-char-pixel-width window face))
+           (ncols (/ window-width font-width)))
+      (if (and (display-graphic-p)
+               overflow-newline-into-fringe
+               (/= (frame-parameter nil 'left-fringe) 0)
+               (/= (frame-parameter nil 'right-fringe) 0))
+          ncols
+        (1- ncols)))))
+
 (provide 'window)
 
 ;;; window.el ends here