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Re: Speed of keyboard macro execution?

From: Perry E. Metzger
Subject: Re: Speed of keyboard macro execution?
Date: Thu, 10 Dec 2015 13:10:37 -0500

On Thu, 10 Dec 2015 19:53:11 +0200 Eli Zaretskii <address@hidden> wrote:
> This I can explain.  "Redisplay" comes into play not only for
> actually redrawing the screen, it also comes into play when, e.g.,
> a command moves cursor down, as in C-n.  With (the default)
> line-move-visual mode, Emacs no longer has an easy way of knowing
> what character is directly below the current one, what with all the
> variable-pitch fonts and long lines broken between several screen
> lines.  The only way of finding out where is "one visual line down"
> is to _simulate_ redisplay.  IOW, Emacs runs code that does exactly
> what redisplay does, but without displaying anything; it just
> accumulates pixel coordinates until it finds itself one visual line
> down.

Oh, my. Now I understand. Especially once you have issues like (as
just one example) complicated Unicode rendering involved, this could
get arbitrarily messy.

I suppose there are only two obvious ways to handle that:

1) radically speed up the redisplay code.
2) memoize the output of the redisplay code.

Have I missed an obvious approach or are those the choices?

Perry E. Metzger                address@hidden

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