[[Someone have URLs for what '''TrueType''' is, etc.?
Google suggests http://www.truetype.demon.co.uk/ as one possible site - appears to have a history and other information about the technology.  Note that Microsoft no longer provides their set of TrueType web fonts for people to download.

[RS]: Name of a company (later bought by [Microsoft]) which produced scalable vector fonts of good quality for Macintosh, later also for Windows. TrueType fonts typically have the extension .ttf. The format is sort of portable so that TTF fonts from large Windows desktops also work well on [PocketPC]s. I like most the quick reaction: you can resize a font in a Tk widget e.g. with a [scale] and have it react in about real time.

[KPV]: Microsoft TrueType page is http://www.microsoft.com/typography/users.htm.
----
[BR]: TrueType fonts were made popular by their support in [Microsoft Windows] since 3.1
(?) and on Apple's [MacOS].

Since the creation of the [FreeType] library TrueType fonts are supported by [X11]-based
system in various forms.  Currently the font server in XFree86 and its derivates can use
TrueType files through this library.  More sophisticated support on [X11] is possible with 
the Xft library (there is a compile-time switch for Tk to use this, see [Xft support]).

TrueType fonts are not only scalable (as opposed to the bitmapped fonts that are still
the basis of X11 text rendering) TrueType  is also an extensible format, which means that
vendors can add new data if they need that for more complicated scripts.

There are currently two major such extension systems on the market, OpenType
[http://www.opentype.com], [http://www.microsoft.com/typography/], by Adobe and Microsoft,
and AAT [http://developer.apple.com/fonts/], by Apple (both the Microsoft and Apple sites
also have the base specifications).  Both extension systems define the format of information
to add into fonts about ligatures, shaping and bidi.  Both extensions can coexist in the
same font file.

OpenType is supported by [Microsoft Windows] and on [X11] by Pango (part of [GTK]),
AAT is supported by [MacOS X].  It is planned to get better support for OpenType on
Unix systems, see the "FreeType Layout" link [http://www.freetype.org/ftlayout/index.html]
on the [FreeType] site.

Curiously, while Adobe has co-authored OpenType, and PostScript does have basic
TrueType support, PostScript does not seem to use the OpenType extensions yet
automatically.  Unless somebody can point me to some better information on that
question?

[Lars H]: As I recall it, the ''main'' difference between TrueType and OpenType
is that the latter adds support for '''CFF''' outlines, where the font is 
defined in terms of [Postscript]-style cubic Bezier curves, whereas the 
original TrueType outline format '''sfnt''' is based on the same type of 
quadratic splines that one gets from a [canvas] polygon item with 
''-smooth true''. There may certainly be other things that were added to
the standard at the same time, but this is the big difference. Fonts with
sfnt outlines generally carry a .ttf suffix, whereas fonts with CFF outlines
generally carry an .otf suffix.

As for more advanced typographic information in the font and its relation
to Postscript, I think these are meant to live on different levels. 
Remember that PS doesn't even have any built-in mechanism for kerning 
(beyond some variants of the show operator that allows you to give the 
string to print intermingled with metric adjustments). Presumably it is
instead the responsibility of the program generating the PS to make use
of more advanced typographic information, when there is any.
(Presumably the program is furthermore expected to work through the OS 
when retrieving this information, rather than directly reading the font
file. This could be a major show-stopper for cross-platform functionality.)
----
An alternative for scalable fonts, but less widely used on displays, are [Postscript]
fonts.
----
[[
[Category Characters]
]]