bug#1562: 23.0.60; modify-frame-parameters in Emacs 23 for fonts

["Drew Adams" <drew.adams@oracle.com>]

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> > (1) `modify-frame-parameters' changes the `font' parameter 
> > behind your back from the value you provide
> > `modify-frame-parameters':
> >
> > (modify-frame-parameters frame
> >   (list (cons 'font "-outline-Lucida Console-normal-normal-\
> > normal-mono-15-*-*-*-c-*-iso8859-1")))
> >
> > The `font' frame parameter is then:
> >
> > "-outline-Lucida Console-normal-normal-normal-mono-15-\
> > *-*-*-c-*-fontset-auto8"
> >
> > IOW, iso8859-1 gets replaced by fontset-auto8.
> 
> I don't see this. Please try with emacs -Q.

See attached file, bug-zoom.el.
emacs -Q, then load the file or eval it a sexp at a time if you want to see the
initial font name etc.

After loading, (frame-parameter nil 'font) gives
"-outline-Lucida Console-normal-normal-normal-mono-14-*-*-*-c-*-iso8859-1"

Then do `C-u 5 M-x enlarge-font'. (frame-parameter nil 'font) gives
"-outline-Lucida Console-normal-normal-normal-mono-19-*-*-*-c-*-iso8859-1"
which is correct.

Then do `C-u -5 M-x enlarge-font'. (frame-parameter nil 'font) gives
"-outline-Lucida Console-normal-normal-normal-mono-14-*-*-*-c-*-fontset-auto1"
which is NOT correct.

The code calls `modify-frame-parameters' with the same 14-point font name that
was returned initially, and which ends in "-iso8859-1", not "-fontset-auto1".
But that's not what the `font' parameter value is after the
`modify-frame-parameters' call.

`M-x debug-on-entry enlarge-font', and you will see, just after this call
(notice that the font name passed as argument is correct):

Debugger entered--returning value: nil
  modify-frame-parameters(#<frame emacs@DRADAMS-LAP1 0x2acf600> ((font .
"-outline-Lucida Console-normal-normal-normal-mono-14-*-*-*-c-*-iso8859-1")))

that (frame-parameter nil 'font) gives
"-outline-Lucida Console-normal-normal-normal-mono-14-*-*-*-c-*-fontset-auto1"
which is wrong.

(I also tried using `copy-sequence' to ensure that the string passed is a new
one etc. No improvement.)

Initially, I thought perhaps it had something to do with the call to
`query-fontset' in the commented-out piece of code in `enlarged-font-name',
since `query-fontset' returns a string with "-fontset-auto1" at the end. But the
bug remains, even with that code commented out.

Note too that over time, "-fontset-auto1" becomes "-fontset-auto2", and so on.

The bug seems to be in `modify-frame-parameters'.

FWIW, let me be clear why I would like this bug fixed. While waiting for the
fix, I hacked the code for Emacs 23 to just modify the :height attribute for the
`default' face. That is what most people do, to zoom a frame. That does not give
as many font/frame size possibilities as my code does - it is not as flexible.
So yes, I know there is a rudimentary workaround, but I would like this code to
work again, as it does in Emacs 20, 21, and 22. It doesn't seem right that
`modify-frame-parameters' modifies a frame differently from what you tell it to
do.


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(modify-frame-parameters
 nil
 (list
  (cons 
   'font
   "-*-Lucida Console-normal-r-*-*-14-*-96-96-c-*-iso8859-1")))

(frame-parameter nil 'font)

(defun enlarge-font (&optional increment frame)
  "Increase size of font in FRAME by INCREMENT.
Interactively, INCREMENT is given by the prefix argument.
Optional FRAME parameter defaults to current frame."
  (interactive "p")
  (setq frame (or frame (selected-frame)))
  (let ((fontname (cdr (assq 'font (frame-parameters frame))))
        (count 100))
    (setq fontname (enlarged-font-name fontname frame increment))
    (while (and (not (x-list-fonts fontname)) (wholenump (setq count (1- count))))
      (setq fontname (enlarged-font-name fontname frame increment)))
    (unless (x-list-fonts fontname) (error "Cannot change font size"))
    (modify-frame-parameters frame (list (cons 'font fontname)))
    ;; Update faces that want a bold or italic version of the default font.
    (frame-update-faces frame)))

(defun enlarged-font-name (fontname frame increment)
  "FONTNAME, after enlarging font size of FRAME by INCREMENT.
FONTNAME is the font of FRAME."
;;   (when (query-fontset fontname)
;;     (let ((ascii (assq 'ascii (aref (fontset-info fontname frame) 2))))
;;       (when ascii (setq fontname (nth 2 ascii)))))
  (let ((xlfd-fields (x-decompose-font-name fontname)))
    (unless xlfd-fields (error "Cannot decompose font name"))
    (let ((new-size (+ (string-to-number (aref xlfd-fields xlfd-regexp-pixelsize-subnum))
                       increment)))
      (unless (> new-size 0) (error "New font size is too small: %s" new-size))
      (aset xlfd-fields xlfd-regexp-pixelsize-subnum (number-to-string new-size)))
    ;; Set point size & width to "*", so frame width will adjust to new font size
    (aset xlfd-fields xlfd-regexp-pointsize-subnum "*")
    (aset xlfd-fields xlfd-regexp-avgwidth-subnum "*")
    (x-compose-font-name xlfd-fields)))