Re: [Freetype] Caching glyph metrics

[David Turner]

Hi Michael,

Michael Day a écrit :
> 
> > > What do you not understand in the cache sub-system ? Are you aware of the
> > > following draft (that is part of the "ft2docs" package):
> > >
> > >   http://www.freetype.org/freetype2/docs/cache.html
> 
> I've written a basic glyph metrics cache by copying the image cache,
> however I've noticed that linearHoriAdvance (which I need) is stored in
> the glyph slot rather than the glyph metrics. Any particular reason for
> that?
>

Yes. There are several reasons:

  - because the glyph metrics structure is used to report the
    metrics of the current glyph image, which is generally
    altered by hinting (or embedded bitmap substitution)

  - because it's in different units than the rest of the
    glyph metrics (i.e. 16.16 fixed point pixels or integer
    font units)

  - to encourage application developers to realize that they
    should not use it to perform text layout naively.

    at low resolutions, this always produces crap results.
    at high resolution, you'd better use the hinted metrics
    anyway, since you shouldn't spot the difference

    and if you want to be WYSIWYG, you should only use them
    to compute line lengths, use the hinted metrics to
    compute glyph placement on the line, while adjusting
    inter-word or even inter-letter spacing to correct for
    any difference between the hinted and linear line width..

Hope this is clear..

- David Turner
- The FreeType Project