RE: ligature usage - WAS: How do we find out what assigned code points aren't normally used in text?

There's no requirement that the width of glyphs in a monospaced font be 1 em. I would agree, though, that if a monospaced font forms a ligature of a pair like <0066, 0069>, then it should be twice the width (not necessarily 2em) of single-character glyphs.

In a monospace font, nothing prevents the glyph for FB01 being a ligature, and some monospaced fonts do have a ligature glyph for that character.

Of course, in a monospaced font, the glyph for that character should be the same width as all other glyphs. So if it's not a ligature, then the "f" and "i" elements still need to be narrower than the glyphs for 0066 and 0069.

Hence, in a monospaced font, FB01 certainly should look different from <0066, 0069>, regardless of whether ligature glyphs are used in either case.

Peter

-----Original Message-----
From: unicode-bounce_at_unicode.org [mailto:unicode-bounce_at_unicode.org] On Behalf Of Philippe Verdy
Sent: Saturday, September 10, 2011 10:33 PM
To: Michael Everson
Cc: unicode Unicode Discussion
Subject: Re: ligature usage - WAS: How do we find out what assigned code points aren't normally used in text?

2011/9/11 Michael Everson <everson_at_evertype.com>:
> On 11 Sep 2011, at 00:23, Richard Wordingham wrote:
>
>> A font need not support such ligation, but a glyph for U+FB01 must
>> ligate the letters - otherwise it's not U+FB01!
>
> Not in monowidth, it doesn't.

I also agree, a monospaced font can perfectly show the dot and ligate the letters, using a "double-width" (2em) ligature without any problem, or simply not map it at all, or choose to just map a composite glyph made of the 1em-width glyphs assigned to the two letters f and (dotted) i without showing any visible ligation between those glyphs (this being consistant with monospaced fonts that remove all ligations, variable advances and kernings between letters).

You could as well have a font design in which all pairs or Latin letters are joined, including in a monospaced font, in which case you should not see any difference between FB01 and the pair or Basic Latin letters. Joining letters is fully independant of the fact that the upper part of letter f may or may not interact graphically with the presence of a dot. If the style of letter glyphs does not cause any interaction, there's no reason to remove the dot over i or j in the "ligature" or joining letters.

You should not be limited by the common style used in modern Times-like fonts (notably in italic styles, where the letter f is overhanging over the nearby letters). Other font styles also exist that do not require adjustment to remove the dot, or merge it with a graphic feature of the preceding letter f which is specific to some fonts.

As the pair of letters f and (dotted) i is perfectly valid in Turkish, there's absolutely no reason why the fi ligature would be invalid in Turkish. But given that this character is just provided for compatibility with legacy encodings, I would still not recommand it for Turkish or for any other language, including English. This FB01 character is not necessary to any orthography and if possible, should be replaced by the pair of Basic Latin letters (and in fact I don't see any reason why a font would not choose to do this everywhere)

-- Philippe.
Received on Sun Sep 11 2011 - 12:00:33 CDT