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Re: Something like `without-redisplay'?


From: Eli Zaretskii
Subject: Re: Something like `without-redisplay'?
Date: Tue, 01 Sep 2015 05:39:42 +0300

> Date: Tue, 1 Sep 2015 01:37:22 +0200
> From: Alexander Shukaev <address@hidden>
> Cc: help-gnu-emacs <address@hidden>
> 
> (defmacro devil-without-window-hscroll
>     (&rest body)
>   "\
> Execute BODY without horizontal scrolling in the selected window."
>   (declare (debug  t)
>            (indent defun))
>   `(let ((hscroll (window-hscroll)))
>      (set-window-hscroll (selected-window) 0)
>      (unwind-protect
>          (progn ,@body)
>        (set-window-hscroll (selected-window) hscroll))))
> 
> In brief, these are macros which somehow alter viewport (how window
> views a buffer) temporarily and then restore it.

I don't understand the need for that: since redisplay doesn't happen
as long as the code runs, why would you need to manipulate the
viewport like that during the execution, just to have it back by the
time redisplay is about to happen?

> For instance, if `auto-hscroll-mode' is on, should I fear that
> `set-window-hscroll' will move point?  I personally, have not
> experienced this problem, but still I want to know exactly what to
> expect.  For example, would you recommend to wrap
> `set-window-hscroll' into `save-excursion' or that would be
> redundant?  By the way, the same would apply to vertical changes in
> viewport (due to vertical scrolling, for example) as Emacs
> auto-scrolls (moves point to keep it in viewport) by default.  Yet,
> again, I've never experienced any problem with this too.

In general, hscroll only scrolls if point goes out of view.  Vertical
scroll can happen even with point is in view, under some rare
situations.

But again, I don't understand what you want to accomplish with these
macros, so I cannot answer your questions yet.



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