bug#30553: 26.0.91; underline appears beneath line-spacing rather than beneath text

[Eli Zaretskii]

> From: Aaron Jensen <aaronjensen@gmail.com>
> Date: Mon, 26 Feb 2018 12:21:44 -0800
> Cc: Alp Aker <alptekin.aker@gmail.com>, 30553@debbugs.gnu.org
> 
> On Mon, Feb 26, 2018 at 11:25 AM, Eli Zaretskii <eliz@gnu.org> wrote:
> > "All" meaning the two involved in the underline position, right?  Yes,
> > that would be a good addition, I think.
> 
> Ok, I'll submit a separate patch for that.

Thanks.

> > So it's spacemacs' fault, perhaps exasperated by choosing some font
> > and/or colors that make this issue more prominent.  Right?  Then how
> > about asking the spacemacs developers to improve the situation on
> > their end?
> 
> No, spacemacs is setting x-underline-at-descent-line t because of
> bug#30609, I would guess.

Bug#30609 does not describe a bug, IMO.  Drawing display elements with
background and decorations needs to be done in some order, and
whatever order we chose, we will have some issues.  AFAIU, the current
order has the fewest issues, which only appear when certain fonts
and/or certain colors are used.

> By "this variable" I meant the one I introduced in my patch. Are you
> still interested in accepting that?

No, I don't think it will solve any problem that the two existing
variables cannot.

> 1. I will submit a patch to make the two existing underline variables
> work buffer local.
> 
> 2. It would be great if we could figure out a way to address
> bug#30609.

I don't see how, and I told that much in that bug report.  But I'm far
from being a GUI display expert, so maybe someone else will come up
with a solution.

> 3. I have the previously attached patch which adds a new variable that
> draws the underline below the descenders rather than at the bottom of
> the overall descent.

IMO, it's better to make x-underline-at-descent-line a tristate
variable than add another boolean.