Re: Fill column indicator functionality

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 16 Mar 2019 10:36:10 +0100
> From: Ergus <spacibba@aol.com>
> Cc: emacs-devel@gnu.org
> 
> I tried that solution (setting the :height attribute to 1.0 in the face
> declaration) and it didn't work.

Well, I'm not really surprised, it was a long shot.

> I see that there is a calc_line_height_property; can we use that to
> change the glyph. Maybe it is possible to implement a setter (equivalent
> to get_it_property?

I don't think I understand the proposal.  calc_line_height_property is
used to produce line-spacing, but I don't see how it could be used for
enlarging the font, since AFAIK that can only be done via a face
definition.

> We can compare the line height with the it height and change it
> temporarily to print the indicator?

That won't help, because the code we are talking about doesn't draw
anything, it just prepares the data structures for drawing.  the
actual drawing happens later, and it is terminal-dependent (for X, see
xterm.c, the function x_draw_glyph_string_foreground, for example).

I think, unless some clever idea comes up which will allow us to use
an existing feature, we should for now leave this issue alone, because
avoiding the gap between indicators when line height varies will
probably require adding some display features, and the indicator
display shouldn't be held off till we do.