Re: Fill column indicator functionality

[Ergus <spacibba@aol.com>]

On Fri, Mar 15, 2019 at 04:59:16PM +0000, Drew Adams wrote:

Hi Drew:

>(Caveat: I haven't really been following this thread.
>Apologies if I misunderstand the intention or the
>scope, e.g., if this is off topic.)
>
>I guess y'all are trying to come up with the ability
>to have vertical display lines similar to window
>dividers - maybe 1-pixel wide (or configurable as
>N pixels wide?).
>
>Keith is apparently working on such a thing for a
>fake-cursors implementation.  And this thread is
>about using such a thing for indicating the fill
>column.
>

Not really, this patch is a much much simpler solution for a much much
less complex use case.

The fci functionality is in my opinion a very basic code editor
functionality and the solution already available was going to be
unmaintained and had incompatibilities with show-trailing-whitespace.

Eli replied to this a couple of days ago.

Up to now I implemented this to add 1 single vertical line to a
position, the expansion to multiple lines is something possible, but I
don't find a general enough use case that deserves to do so; but if we
find one we can work on that in the future.

I didn't want to over-specify the functionality or produce excessive
overhead in a key place like the display engine. So being a KISS was
part of the intention.

>Do I understand that right?  If so, will the approach
>to doing this be general, so the same implementation
>(in C) can be used for both of these applications?
>

I don't think so; at least not in an easy way. 

>In that case, could it also be used also for vertical
>lines separating table cells and other things.
>
I think that those use cases must be better implemented in elisp as the
use cases will be very specific.

>If so (if we'll have a general feature for such
>support) will there be something similar for
>horizontal lines?

This one is easy, to implement if it is not already; but I don't think
it even requires to go in the display engine. 

>And will we be able to limit
>such lines (start and stop positions), or will

If there is a real use case we can add that functionality, but now it is
not implemented.

>they always be across an entire window?

For now yes.

I hope this answers all your doubts?