Re: [ft] Vert advance on line break

[Mickey Gabel]

Werner:
> From the documentation of FT_FaceRec:
>
>   height        
>
>     The height is the vertical distance between two consecutive
>     baselines, expressed in font units.  It is always positive.  Only
>     relevant for scalable formats.
>
> Or do you mean something different?
>
>       Werner

mpsuzuki and Disch:
> >                       I tried using [i]face->size->metrics.height[/i], but
> > this seemed far too steep for some fonts (almost like the font was
> > double-spaced), and simply doesn't exist at all (is zero) for many, many
> > fonts such as Courier, which makes it completely useless for me.
>
> Yeah, it notices the height of glyph, not the space between
> the lines. Usually, the calculation of the space between the
> lines is not recognized as the role of the fonts.
>
> > This is a seemingly simple question, yet the tutorials fail to mention
> > anything about it, the documentation leaves it unclear, and I've even tried
> > searching this forum with no success (someone asked the question, then
> > replied saying they found the answer -- but never said what the answer is).
>
> Maybe you want to pass "single space" or "double space" to
> some FT2 API and receive the appropriate shift from the
> previous line to current line, but such 2D layout work is
> for more intelligent layout systems. In fact, the LineGaps
> in hhea & OS/2 are no more than the minimum space. Some font
> file formats does not provide such informations at all. It
> would be the reason why FT2 tutorials don't describe line-to-
> line process.

Werner:


1) What about "line gap" (aka "external leading") mentioned in 
docs/glyphs/glyphs-3.html (Glyph Convension)? How does FT2 get this line 
gap if it's not specified in the font?
2) If FT2 does get it, how do I get this line gap / external leading 
from FT2?
I thought face->size->metrics.height IS the way to get it!
3) It seems mpsuzuki and Werner have two contradicting answers :(
Werner says "use height", mpsuzuki says "don't use it, it's wrong".
Can you help clarify?
4) Does FT2 use the hhea table in anyway by itself? (for example to 
initialize the FaceRec "height" member?
5) We sometimes use (2 + ascender - descender) as a the line height. 
This seems to work, and may be useful workaround so I mentioned it here.

Thanks,
        Mickey