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Re: rmsbolt.el [Was: Colorful line numbers]

From: Stefan Monnier
Subject: Re: rmsbolt.el [Was: Colorful line numbers]
Date: Sat, 23 Jul 2022 12:31:52 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (gnu/linux)

>> > The big difference from my POV is that text properties slow down
>> > redisplay code
>> If that's indeed a problem, then maybe we should provide "non-display
>> text-properties".  I.e. text-properties which do not influence the
>> display, so we can store them in a parallel interval tree
> That's quite a complication.  For starters, how to make sure the same
> property doesn't get stored in both trees?  Next, redisplay aside,
> most if not all properties that are important for redisplay are also
> important to Lisp, and so Lisp programs will now have to look at two
> interval trees.

If we need/want to solve those problems, I don't see any
technical difficulty.  Until we have found it necessary, the question is moot.

>> (tho we'd have to check whether the source of the slowdown is the
>> interval tree itself or the length of the `plist`s stored in its
>> nodes, so maybe we could have a single tree but with two `plist`
>> fields, one for display-related properties and the other for
>> non-display-related properties).
> The immediate source of slowdown is that the display iterator stops at
> every position where the properties change, and runs all of its
> "handle stop-point" handlers, each one of which examines the
> properties it handles (fontified, face, invisible, and display).
> For what we do with the tree and the properties we find, see
> compute_stop.

So adding a text property for the line numbers's face would (in
the worst case) add 2 "handle stop-points" per line (could be reduced
to one by making those properties cover the whole "line plus newline"
so there's only one stop-point between them).

Could that really cause a measurable slow down?


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