bug#20628: 25.0.50; Incorrect line height for some fonts

[Eli Zaretskii]

> Date: Sun, 24 May 2015 04:20:32 -0400
> From: Clément Pit--Claudel
>  <clement.pitclaudel@live.com>
> CC: ohwoeowho@gmail.com, 20628@debbugs.gnu.org
> 
> I looked a bit more into how other programs handle this, and it seems that 
> they take the simple approach of relying on font-wide metrics. Only, they 
> don't seem to use the same ones as Emacs. This causes LibreOffice and vim-gtk 
> to display "∫" as slightly truncated when using Latin Modern Math (it's 
> taller than the line height). Emacs on the other hand displays it fine (at 
> the cost of having a huge line height.
> 
> I wonder if changing the set of metrics used in Emacs would be easy.

Changing how?  Which metrics to use instead?  We need details to
discuss our options.

And why is it TRT to make a change that clearly results in incorrect
display of some of the glyphs in that font?  It seems we have just
found the answer to the question how do those other programs "avoid"
the problem: they do it at a price of producing incorrect display of
tall glyphs.  I don't think Emacs should go that way.

A better alternative would be to detect such tall glyphs when they are
needed for display, and enlarge the line height only then.  But I
don't yet see the data of these glyphs that could tell us to do that,
any help will be appreciated.