Respect internal window/frame padding

[DivineDominion]

Inspired by https://github.com/rougier/nano-emacs, I have a internal-border-width (see Frame Layout in the manual) set to 24:

(setq default-frame-alist
      (append (list
               '(font . "Roboto Mono-18")
               '(min-height . 1)  '(height     . 45)
               '(min-width  . 1)  '(width      . 101)
               '(vertical-scroll-bars . nil)
               '(internal-border-width . 24) ;; frame padding around the text
               '(left-fringe    . 0)
               '(right-fringe   . 0))))

I noticed that the effective window width calculations wouldn't work as expected -- as a result, lines would wrap.

This change takes the optional internal-border-width into account.

Examples with internal border of 24 and 48, full screen and windowed:

	before (wrapping/truncating)	after (fits)
24px
48px

I noticed that I had to / 2 the border value, otherwise the line would be truncated too much. Still: the larger the internal-border-width, the worse the line actually fits. See the screenshot in the bottom-right at 48px: there's room for 1--2 additional characters.

But I think that's preferable to line-wrapping.

[DivineDominion]

@purcell Pinging just in case you didn't get a notification from the PR itself to see what you think of this.

[purcell]

Hmm, thanks for this, but it's weird — with a recent dev Emacs version, I can't reproduce your wrapping/truncation.

[DivineDominion]

@purcell Could also be macOS and its font rendering in GUI emacs -- there seems to be a somewhat common problem with width calculations. Not sure though if that's the case and subtracting the internal border offset is just a coincidence.

Question is: do my changes look weird on your machine, e.g. is the line too small then?

[purcell]

Question is: do my changes look weird on your machine, e.g. is the line too small then?

No, they actually don't make a difference at all, as far as I can tell, either with or without an internal border.

[purcell]

(Which seems suspicious)

[DivineDominion]

I read up a bit more about frame geometry in Emacs:

https://www.gnu.org/software/emacs/manual/html_node/elisp/Frame-Layout.html
https://www.gnu.org/software/emacs/manual/html_node/elisp/Frame-Size.html

When I query (frame-inner-width nil) and (window-width nil t) I get the same values. So your original approach should just work ™️

I wonder why it's not getting smaller for you though when you use my code. Is (alist-get 'internal-border-width (frame-geometry nil)) not returning the value you set? I updated my code to use that instead of default-frame-alist, too.

[DivineDominion]

I built Emacs 28 from source and the issue disappears. Might've been a faulty build 🤷

[purcell]

Ah, that can happen sometimes. I've frequently experienced subtle breakage in dev versions.