From: John H. Jenkins (jenkins@apple.com)
Date: Wed Apr 30 2003 - 11:06:20 EDT
On Wednesday, April 30, 2003, at 02:27 AM, Raymond Mercier wrote:
> At least this seems to settle in the negative the question as to
> whether they all have the same unicode blocks.
> On my disk the TTC's have two fonts, except for msgothic.ttc which has
> three.
> I just wondered if Microsoft or anyone else had followed firm
> guidlines, or just did it in a more whimsical way. It is hard to see
> the real point of a TTC.
TTC fonts and their rationales are discussed at some length on
Microsoft's typography Web site
(<http://www.microsoft.com/typography/>, specifically
<http://www.microsoft.com/typography/otspec/otff.htm>).
Theoretically, a TTC font can contain an indefinitely large number of
fonts, since the numFonts field is 32 bits. In practice, more than
three or four is unlikely. As explained in the spec, the purpose is to
allow large fonts to overlap their data; if you have two Japanese
fonts, say, one with proportional Roman and one with monospaced, but
identical kanji. Then the huge 'glyf' table can be shared by the two
with the smaller tables (such as 'cmap' and 'name') used to distinguish
them. The result is a single file which contains two fonts but is
considerably smaller than the two individual fonts would be as two
files.
One could also use TTC files to store multiple related fonts even
without overlap. If I had a roman, bold, italic, and bold-italic, I
could put all four into a single TTC file and have them therefore ship
as a single file, rather than four individual files.
==========
John H. Jenkins
jenkins@apple.com
jhjenkins@mac.com
http://www.tejat.net/
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