Re: Fill column indicator functionality

[Ergus]

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?