Thread-topic: How can you control letter spacing using ATSUCreateTextLayoutWithTextPtr ?
User-agent: Microsoft-Entourage/11.2.1.051004
On 12/25/05 4:24 PM, "Edward de Jong" <email@hidden> wrote:
> How does one efficiently offer tighter than normal or wider than
> normal spacing, without resorting to the addition of a special font
> that contains negative width characters, which would require special
> presence tests, and a more complicated install?
ATSUI can do this in two ways: font-controlled, or app-controlled.
Font-controlled letterspacing is represented by the kerning and tracking
features, and relies on data in the font to make the appearance correct.
Thus, a font with a tracking table enables an app developer to provide the
user with, say, a popup menu for "Tight", "Normal" or "Loose" letterspacing,
and the tracking table will control how that happens in a font-sensitive
way.
Kerning is sensitive to which glyphs are adjacent, and adjusts spacing
accordingly. Tracking works irrespective of which glyphs are involved.
App-controlled letterspacing is represented by "with-stream shifts". These
allow you to specify either a positive or a negative amount and spacing
between pairs of glyphs will be adjusted by that amount. This does not rely
on font data; it works with any fonts. Note that both app-controlled
letterspacing and font-controlled letterspacing are handled at the style-run
level, so you can turn the features on and off by making appropriate runs.
Other letterspacing effects are available in ATSUI via justification, but
that's a much more advanced topic. If you're interested, see this
whitepaper:
http://developer.apple.com/fonts/WhitePapers/GXJustification.html
It talks about GX, which was ATSUI's spiritual predecessor. The models are
pretty much the same.
Dave Opstad
Line Layout Weenie (ret.)
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