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

[Aaron Jensen]

On Wed, Feb 21, 2018 at 9:56 AM, Eli Zaretskii <eliz@gnu.org> wrote:
> Feel free to submit patches to introduce this as yet another optional
> behavior.  We cannot just throw out the current behavior, because it
> was with us since Emacs 21.
>
> Note that this feature has 3 implementations, one each in every GUI
> back-end we support.

I changed my mind on this after discovering that these variables do
not work as buffer local variables. Whatever the current buffer has it
set to causes all other visible buffers to draw in that way, which
causes underlines to jump around if they're set differently in
different buffers.

Please see attached patch. I don't have a windows or linux machine to
test on, so if someone could do that it would be appreciated. There
are some subtle differences in the original code which I tried to
respect.

I'm open to any advice on the naming/doc strings or implementation. Thanks!

Aaron

0001-Add-x-underline-below-font-descent.patch
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