bug#74750: clone-frame and make-frame pixelwise issues

[Eli Zaretskii <eliz@gnu.org>]

> From: Ship Mints <shipmints@gmail.com>
> Date: Mon, 9 Dec 2024 10:51:23 -0500
> 
> While trying to reconcile pixelwise frame sizing behaviors, I narrowed down
> two related issues.
> 
> clone-frame does not correctly clone frames on a pixelwise basis.
> 
> make-frame's text-pixels geometry support does not produce specified
> pixelwise geometry. This also impacts frameset-restore's ability to
> precisely reproduce pixelwise frame sizes.
> 
> I consider these to be related as clone-frame's use of make-frame could be
> using text-pixels but if that doesn't work then pixelwise cloning won't
> work. I did read through the code base as best as I could but could not
> find the source of the text-pixels issue.
> 
> The following reproducer, under -Q, shows the same results on 29.4 and
> 30.0.92. My main platform is NS and I also did some testing on GTK. GTK's
> issues seem a bit "messier" and I didn't spend any time trying to
> understand them in depth as I was more interested to know if GTK worked
> correctly or not, which it doesn't.
> 
> (switch-to-buffer "*Messages*")
> (let ((target-text-width 1700)
>       (target-text-height 1000)
>       (native-width)
>       (native-height)
>       (msg (lambda (s frame)
>              (message "%s text-width=%d (Δ%d) text-height=%d (Δ%d)
> native-width=%d (Δ%d) native-height %d (Δ%d)\n"
>                       s
>                       (frame-text-width frame) (- (frame-text-width frame)
> target-text-width)
>                       (frame-text-height frame) (- (frame-text-height
> frame) target-text-height)
>                       (frame-native-width frame) (- (frame-native-width
> frame) native-width)
>                       (frame-native-height frame) (- (frame-native-height
> frame) native-height)))))
>   (set-frame-position nil 0 0)
>   (set-frame-size nil target-text-width target-text-height 'pixelwise)
>   (setq native-width (frame-native-width)
>         native-height (frame-native-height))
>   (message "Targets: text-width=%d text-height=%d\n" target-text-width
> target-text-height)
>   (funcall msg "orig" (selected-frame))
> 
>   (message "clone-frame under frame-resize-pixelwise nil; expectation: use
> lines/columns geometry; outcome: met")
>   (let ((frame-resize-pixelwise nil))
>     (let ((new-frame (clone-frame)))
>       (funcall msg "new" new-frame)
>       (delete-frame new-frame)))
> 
>   (message "clone-frame under frame-resize-pixelwise t; expectation:
> pixelwise geometry; outcome: unmet")
>   (let ((frame-resize-pixelwise t))
>     (let ((new-frame (clone-frame)))
>       (funcall msg "new" new-frame)
>       (delete-frame new-frame)))
> 
>   (message "clone-frame followed by manual resize; expectation: pixelwise
> geometry; outcome: met (but two steps)")
>   (let ((new-frame (clone-frame)))
>     (set-frame-size new-frame target-text-width target-text-height
> 'pixelwise)
>     (funcall msg "new" new-frame)
>     (delete-frame new-frame))
> 
>   (message "manual clone under frame-resize-pixelwise using text-pixels;
> expectation: pixelwise geometry; outcome: unmet")
>   ;; code lifted from clone-frame
>   ;; incorrect width offset seems to be equal to frame-scroll-bar-width
>   (let* ((frame-resize-pixelwise t)
>          (frame (selected-frame))
>          (no-windows nil)
>          (windows (unless no-windows
>                     (window-state-get (frame-root-window frame))))
>          (default-frame-alist
>           (seq-remove (lambda (elem)
>                         (memq (car elem) frame-internal-parameters))
>                       (frame-parameters frame)))
>          (new-frame))
>     (when (and (display-graphic-p frame) frame-resize-pixelwise)
>       (push (cons 'width (cons 'text-pixels (frame-text-width frame)))
> default-frame-alist)
>       (push (cons 'height (cons 'text-pixels (frame-text-height frame)))
> default-frame-alist))
>     (setq new-frame (make-frame))
>     (when windows
>       (window-state-put windows (frame-root-window new-frame) 'safe))
>     (unless (display-graphic-p frame)
>       (select-frame new-frame))
>     (funcall msg "new" new-frame)
>     (delete-frame new-frame)))
> 
> This is an implementation of clone-frame that uses text-pixels under
> make-frame. This depends on make-frame text-pixels being corrected. Happy
> to supply this as a patch should the discussion of these issues progress in
> that direction.
> 
> (defun clone-frame (&optional frame no-windows pixelwise)
>   "Make a new frame with the same parameters and windows as FRAME.
> With a prefix arg NO-WINDOWS, don't clone the window configuration.  When
> PIXELWISE is non-nil or if `frame-resize-pixelwise' is non-nil, and frame
> is not text-only, clone the originating frame's pixel size.
> 
> FRAME defaults to the selected frame.  The frame is created on the
> same terminal as FRAME.  If the terminal is a text-only terminal then
> also select the new frame."
>   (interactive (list (selected-frame) current-prefix-arg))
>   (let* ((frame (or frame (selected-frame)))
>          (windows (unless no-windows
>                     (window-state-get (frame-root-window frame))))
>          (default-frame-alist
>           (seq-remove (lambda (elem)
>                         (memq (car elem) frame-internal-parameters))
>                       (frame-parameters frame)))
>          (new-frame))
>     (when (and (display-graphic-p frame)
>                (or pixelwise frame-resize-pixelwise))
>       (push (cons 'width (cons 'text-pixels (frame-text-width frame)))
>             default-frame-alist)
>       (push (cons 'height (cons 'text-pixels (frame-text-height frame)))
>             default-frame-alist))
>     (setq new-frame (make-frame))
>     (when windows
>       (window-state-put windows (frame-root-window new-frame) 'safe))
>     (unless (display-graphic-p frame)
>       (select-frame new-frame))
>     new-frame))

Thanks.  I hope Martin (CC'ed) will have some useful inputs.