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bug#17303: On tty or -nw, (window-body-width) is one column too big.
From: |
Eli Zaretskii |
Subject: |
bug#17303: On tty or -nw, (window-body-width) is one column too big. |
Date: |
Mon, 21 Apr 2014 09:56:01 +0300 |
> Date: Sun, 20 Apr 2014 20:39:04 +0000
> Cc: 17303@debbugs.gnu.org
> From: Alan Mackenzie <acm@muc.de>
>
> > No, it's because the last character in the continued like is in column
> > 78 on a TTY, but in column 79 in a GUI session. Emacs counts columns
> > in continuation lines starting from the last column in the previous
> > line, as you'd expect. IOW, the continued line is treated as one long
> > line, and all its columns counted contiguously.
>
> Yes, this is true, but it's (window-body-width) which is inconsistent
> between GUI and tty.
>
> > It is true that the "\" character on a TTY takes up one column, and
> > thus leaves only 79 columns for text, but what else can Emacs do?
>
> Tell me that (window-body-width) is 79, not 80.
It can't. It's not designed for what you need. You should use
different APIs for what you want; see below.
> > current-column is it. Please tell why it doesn't fit your needs.
>
> current-column provides the "logical" column (e.g. 79). I need the
> "visual" column (e.g. 0).
Then what you want is '(car (posn-col-row (posn-at-point)))'. But see
below.
> I'm working on getting follow-mode's scrolling working properly. I have
> a situation where:
> o - point is at Col 79, this being at the start of a continuation line.
> o - this position is one line below the bottom of the window
> o - (but hasn't been redisplayed yet).
> o - set-window-start has NOT been called with a nil NOFORCE parameter.
>
> If I were to allow the redisplay without further action, redisplay would
> scroll the window back upwards to ensure point is displayed. This would
> negate the purpose of the scrolling. I want to move point back into the
> window before the redisplay. So I attempt the following:
> o - (setq dest-col (Determine-the-visual-column-point-is-in))
> o - (vertical-motion -1)
> o - (move-to-column dest-col)
>
> However this last action becomes, on a tty, (move-to-column 79) putting
> point back where it started. :-(
I think you just need to use pos-visible-in-window-p instead of all
that complexity: if that function returns an indication that point is
not visible, move it back until it is. There's also the new
pre-redisplay-function hook that you might find useful.
Don't try to outsmart redisplay; instead, ask redisplay to tell you
what it already knows. The functions I mentioned are interfaces
exposed by redisplay for this very purpose.
So can we close this bug report?
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