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

[martin rudalics]

> (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