Re: Tick Reduction

[Eli Zaretskii <eliz@gnu.org>]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: dgutov@yandex.ru,  stefankangas@gmail.com,  emacs-devel@gnu.org
> Date: Wed, 24 Nov 2021 19:41:49 +0100
> 
> There might be a bug somewhere.  I've now added the previously discussed
> `add-display-text-property' function, so now it's easier to test these
> things, and it looks like there's something not quite working as it's
> supposed to, but I haven't debugged yet.  (It only seems to affect
> "overlapping" regions.)

One thing that seems wrong is that you expect handle_stop to be called
at the end of the property.  But that is only true if there's some
text after the property, because handle_stop is called when text
properties _change_, and there's no such change at EOB.  So you need
special handling for EOB and for end-of-string (for the mode-line
case, when the padded field is the last one).

In general, handle_stop and the other functions involved here are used
both when displaying strings and when displaying buffer text, so if
implemented correctly, this feature should automagically work for both
cases.  That's the main reason for implementing the feature at this
level, the level which produces glyphs from some text, regardless of
the origin of that text.