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From: Simon Marshall <Simon.Marshall@esrin.esa.it>
To: XEmacs Beta <xemacs-beta@xemacs.org>
In-Reply-To: <m2wws9cnr9.fsf@altair.xemacs.org> (message from Steven L Baur on
	15 Feb 1997 21:40:10 -0800)
Subject: Re: set-window-redisplay-end-trigger
Reply-To: Simon Marshall <Simon.Marshall@esrin.esa.it>

>> I dunno.  That's what I was trying to find out.  I think I was looking
>> to see if there were any Lisp-visible redisplay hooks and ran into this
>> variable.  Reading the doc string it looks like something that would be
>> useful for lazy-lock and setnu-mode, but I'm not lobbying for it.

sb> Read the comments at the top of lazy-lock.el in Emacs 19.34.
sb> Lazy-lock is the only place I see it referenced in 19.34.

The feature is one of 3 (well 2) that lazy-lock.el version 2 uses to do
correct demand-driven fontification, after scrolling etc.  They are:

1.  window-scroll-functions, run when window-start changes, i.e., the most
common type of scrolling.  This is the thing that usually gets run.

2.  window-size-change-functions, run when window-height changes (or
window-end changes when window-start doesn't I suppose), i.e., when you
do C-x 1 or use the WM to resize or something.  This rarely gets run.

3.  redisplay-end-trigger-functions, run when a given position becomes
visible.  It's used by lazy-lock.el a deletion causes previously invisible
text to become visible at the bottom of the window.

lazy-lock.el doesn't use 3. by default because deferred fontification (and
deferred syntactically true fontification) is on by default.

follow.el also uses 1. and 2.

sb> You could try uncommenting the function to see how it works, but don't
sb> tell Ben.

Hmm, yes.  I think redisplay-end-trigger-functions is the only one Ben
tried to implement, but I don't know why he chose that one.

Si.

