[Libreoffice] Bringing some sanity to interline spacing

[Khaled Hosny]

On Wed, Aug 31, 2011 at 11:54:17PM -0600, Tor Lillqvist wrote:
> > The attached patch is an attempt to bring some sanity to the situation:
> 
> It seems that you have investigate this quite deeply and I would love
> to commit and push your patch. However, I am a bit scared. Could
> somebody else who actually understands the issues involved have a
> look?

I know most of this stuff by heart anyway :) the mess of handling font
vertical metrics across applications and platforms is one of the things
that keeps font developers awake at night.

> > This only done for 'unx' similar work is needed for 'win' and 'aqua',
> > but I'm not familiar with these platforms and can't test on it.
> 
> I wonder if this patch will then introduce significant rendering
> differences between platforms? Or do we have such anyway already (even
> if the same fonts are present)?

For this issues at least we can try to do it the same on all platforms.
I can try to come with patches for Windows and Mac but I was hoping
someone more familiar than me would do it.

After a bit of research, Windows has GetOutlineTextMetrics() that
returns the typographic metrics as opposed to GetTextMetrics() that is
currently used:
http://msdn.microsoft.com/en-us/library/dd144906%28v=VS.85%29.aspx
http://msdn.microsoft.com/en-us/library/dd144941%28v=VS.85%29.aspx

It shouldn't be hard to adapt GetFontMetric implementation in
vcl/win/source/gdi/salgdi3.cxx to use the new function and have the same
logic as the unix code.

The Mac code seems to use the old ATS APIs and I can't find a way to
obtain typographic metrics using it, though it very likely to be
obtaining its metrics from HHEA table which should be the same for typo
metrics in OS/2 table for most fonts. Font designers even consider HHEA
as the Mac metrics table, so it might even be desirable to keep Mac as
is.

> Lastly, can you confirm that your patch is licensed under LGPLv3+ and
> MPL1.1?

Like my previous patches, all are LGPLv3+ and MPL1.1 licensed (though
the patch have been already committed :) )

Regards,
 Khaled

-- 
 Khaled Hosny
 Egyptian
 Arab