Add new functions for computing character metrics for windows

* doc/lispref/display.texi (Size of Displayed Text): Document the
char functions.
* doc/lispref/windows.texi (Window Sizes): Document
window-max-characters-per-line.

* lisp/window.el (window-char-pixel-width)
(window-char-pixel-height)
(window-max-characters-per-line): New functions (bug#19395).

1 files changed, 14 insertions, 0 deletions

diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index becf7ecd157..390d1650253 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -2252,6 +2252,20 @@ This is a convenience function that uses @code{window-text-pixel-size}
 to compute the width of @var{string} (in pixels).
 @end defun
 
+@defun window-char-pixel-width &optional window face
+Return the average character width for the font used by @var{face} in
+@var{window}.  If @var{face} is @code{nil} or omitted, the
+@code{default} face is used.  If @var{windows} is @code{nil} or
+omitted, the currently selected window is used.
+@end defun
+
+@defun window-char-pixel-height &optional window face
+Return the average character height for the font used by @var{face} in
+@var{window}.  If @var{face} is @code{nil} or omitted, the
+@code{default} face is used.  If @var{windows} is @code{nil} or
+omitted, the currently selected window is used.
+@end defun
+
 @defun line-pixel-height
 This function returns the height in pixels of the line at point in the
 selected window.  The value includes the line spacing of the line