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RE: [ft] scalable font metrics, ascent/descent/height, metrics struct
From: |
Turner, David |
Subject: |
RE: [ft] scalable font metrics, ascent/descent/height, metrics struct |
Date: |
Wed, 1 Jun 2005 14:14:57 +0200 |
> 1. There is discrepancy between the calculated metrics (under DIY) and
> those retrieved from the OpenType OS2 Table. i.e. If I compare
> winAscender/winDescender with Latin-1 in the Times New Roman, or the
> ascender under OS2 table and DIY in the New Courier. Do you know why?
>
> 2. This _really_ puzzles me. I call FT_Set_Pixel_Sizes to set the
> character dimensions of the desired face object (in the way shown in
> the attached source code.) But if I sum up any pairs of
> ascender/descender none of them are close to the set size. Do you
> know why?
>
Yes:
- first, the ascender/descender values embedded in the fonts are
most of the time incorrect. We do some magic within FreeType
to re-compute some of them in order to match Windows behaviour,
since this was asked by users.
- second, even when they're correct, the value returned in the
FT_Size metrics are only scaled version of the global values
found in the font. But processes like hinting (automatic or
not) generally make them differ from the real ones.
- David Turner
- The FreeType Project (www.freetype.org)
> > > 2. What is "AFM file" as mentioned in sTypoAscender and
> sTypoDescender
> > > documentation?
> >
> > Adobe Font Metrics files are text files which accompany Type 1
> > PostScript fonts (which don't contain metrics information). On
> > Windows box you'll sometimes fine PFM files which are something
> > similar.
> >
> >
> > Werner
>
> Thanks very much again for your help Werner. Your responses have been
> very helpful.
>
> Anson
>
- RE: [ft] scalable font metrics, ascent/descent/height, metrics struct,
Turner, David <=