bug#19395: 25.0.50; Setting left fringe to 0 messes up window-width

[martin rudalics <rudalics@gmx.at>]

 > (defun window-char-width (&optional window face)
 >     "Return character width for WINDOW.
 > WINDOW must be a live window and defaults to the selected one.
 >
 > FACE is the face for which character width should be
 > returned.  Buffer-local face remappings are applied.  If nil, the
 > default face is used."
 >     (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-max-characters-per-line (&optional window face)
 >    "Return the number of characters that can be displayed
 > on one line.
 > WINDOW must be a live window and defaults to the selected one.
 >
 > FACE is the face whose character width should be used for the
 > calculation.  Buffer-local face remappings are applied.  If nil,
 > the default face is used.
 >
 > This function is different from `window-body-width' in that it
 > accounts for fringes (when at least one fringe has zero width,
 > one column is reserved for continuation characters) and for the
 > size of the default font (which may have been adjusted using,
 > e.g., `text-scale-increase')."
 >    (with-selected-window (window-normalize-window window t)
 >      (let* ((window-width (window-body-width window t))
 >             (font-width (window-char-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)))))
 >
 > Note that the first function is a variant of Martin's version which had
 > a bug: if the buffer in the specified window is displayed in two frames,
 > the returned character width was always the one used in the current
 > frame which is not necessarily the character width in the specified
 > window (the window may be in the other frame).  This is a problem
 > because character width can be different, if the two frames use
 > different default fonts.

So this what I've been trying to find out all the time.  The faces
apparently _get_ merged dependent on the buffer _and_ the frame.

I need a corresponding `window-char-height' as well, probably also with
a FACE argument.

 > For completeness, it probably also makes sense to include the following
 > function in simple.el, which already has a function
 > `default-font-height'.
 >
 > (defun default-font-width ()
 >    "Return the width in pixels of the current buffer's default face font.

I profoundly dislike the "default-" prefix here.  `buffer-font-height'
and `buffer-font-width' would be much better IMHO.

 > I also added the bonus feature which lets you specify a specific face
 > that should be used for the calculations.

So are you now sure that we don't need a specific character ("M") any
more?

martin