From: Eric Muller (firstname.lastname@example.org)
Date: Wed Aug 24 2005 - 15:29:39 CDT
Michael Everson wrote:
> At 18:06 +0100 2005-08-24, Bob Hallissy wrote:
>> It is technically impossible, at least as far as TrueType and
>> OpenType are
>> concerned, as these formats can contain a maximum of 65535 glyphs, and
>> there are more characters than that in Unicode.
> Why can't that be changed? Just curious.
The format is essentially binary, and there are *many* places that
specify a sixteen bit slot for a glyph id; extending the format would be
a major undertaking in itself. Furthermore, to ensure that existing
fonts are still valid, this would essentially lead to a duplication of
most of the tables, etc. Then, all implementations (layout engine,
tools, etc) would have to be extended, and some cannot be easily
touched. Then, there are all the formats derived from TT/OT which may
have inherited the 16 bit limit. Then, there are all the implementations
of those formats.
This is considerable work that has to be justified by the result: the
ability to create a single font that covers all of Unicode. Even if the
sixteen bit barrier was removed, the likelyhood of such a font to ever
exist is essentially nil; it is already the case that we do not have a
complete coverage of Unicode in any number of fonts. Furthermore, the
mere complexity of such a font would be close to intractable; certainly,
it would have many bugs for a long time, making it not too useful anyway.
Finally, there are other problems which cannot be addressed by a single
font, and more or less require some kind of font aggregation mechanism.
When you have such a mechanism, the need for a single font decreases
So, yes, the limit can be removed, but the benefit is not worth the cost.
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