Re: [Freetype] metric differences Freetype vs. Truetype

[David Turner]

Marc L Cohen wrote:
> > > Advance widths?
> >
> > Yes, the hinter can change the width of a gliph.
Or more precisely, it can change both the width and the
"advance width" (a.k.a. "horizontal advance" or "horizontal
escapement"). Even the Postscript and native TrueType hinter
have this ability..

> There is a difference between changing the width of the ink of a glyph and
> the advance width, space to the next glyph. Changing the advance width can
> have very serious effects on the layout of text, especially the nuerals,
> which should all have the same advance width to allow vertical columns of
> the digits.
To avoid confusion, I'll add that "space to the next glyph" is not
a correct description of the advance. Instead, it is the distance
used to increment the pen position during layout and rendering.

Many fonts use the same advance for all digits, but many others
simply do not ! The auto-hinter doesn't treat digits specially, and
will alter them more or less "randomly" when compared to their
linearly scaled value. This can cause some problems in certain
cases, though you're the first to complain on that.

Seems it will be a good idea to hard-code a few specific rules to
deal with this in the auto-hinter. It's very similar to what is
already done for blue values and shouldn't be too hard to code..

Regards,

- David Turner
- The FreeType Project  (www.freetype.org)


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