ct ligature

Please try to keep all the discussions in the main forums on topic! If you have anything else, related to fonts, you want to share, please post it here!
Post Reply
William
Top Typographer
Top Typographer
Posts: 1994
Joined: Tue Sep 14, 2004 6:41 pm
Location: Worcestershire, England
Contact:

ct ligature

Post by William » Wed Jun 11, 2008 9:30 am

I have learned a lot from studying this thread.

Regarding the ct ligature.

I notice that you have the following line in the lookup dligSub section.

sub c t -> ct;

I also notice that the lookup ligaSub section has no mention of the ct ligature.

In Unicode there are three ways to express the ct sequence.

The first is just to use ct as it stands, so that whether or not to use a ligature depends upon whether the font has a glyph for a ct ligature and upon the ability of the application program using the font and upon the discretion of the person using the font. Here is that sequence. ct

Another choice is specifically to request a ligature. The request may not be able to be granted, yet plaintext can record the request. This can, for example, be useful if one is transcribing the text of an early printed book.

To do this, a U+200D ZERO WIDTH JOINER character is used between the c and the t. Here is that sequence. c‍t

The U+200D ZERO WIDTH JOINER character, which is often referred to as ZWJ which, as it name implies should be of zero width, is nonetheless sometimes included in fonts as a visible glyph so that a non-OpenType application can detect that it is being used. The design of the visible glyph is non-standard. Some fonts, such as Arial and Times New Roman, use a vertical line with a small x on top. In my own Chronicle Text font I have used my own design of ZWJ glyph for the U+200D character.

The other choice is specifically to request that a ligature not be used, even if a glyph is available.

To do this, a U+200C ZERO WIDTH NON-JOINER character is used between the c and the t. Here is that sequence. c‌t

The U+200C ZERO WIDTH NON-JOINER character, which is often referred to as ZWNJ which, as it name implies should be of zero width, is nonetheless sometimes included in fonts as a visible glyph so that a non-OpenType application can detect that it is being used. The design of the visible glyph is non-standard. Some fonts, such as Arial and Times New Roman, use a vertical line. In my own Chronicle Text font I have used my own design of ZWNJ glyph for the U+200C character.

Suppose that a transcribed text has been prepared and that it uses c‍t in the transcript specifically to indicate that a ct ligature was used in the original printed text.

As far as I can tell, a font needs a line in the lookup ligaSub section so that the three character sequence c ZWJ t results in the use of a ct ligature glyph. It is not quite clear to me how to do that at present. The postscript name that FontCreator assigned to the ZWJ character is afii301 yet I am unsure as to whether that is the glyph name needed in the lookup ligaSub section. FontCreator assigned the postscript name afii61664 to the ZWNJ glyph. However, ZWNJ does not need to be referred to in the lookup ligaSub nor in the lookup dligSub section. The ZWNJ character works automatically, as the presence of the ZWNJ character between the c and the t means that the ct sequence as such does not occur and so is not recognized, meaning that a ligature glyph is not displayed, which is the desired effect.

For the convenience of readers trying experiments using WordPad and sequences involving ZWJ and ZWNJ I mention that ZWJ is Alt 8205 and that ZWNJ is Alt 8204.

William Overington

11 June 2008

Bhikkhu Pesala
Top Typographer
Top Typographer
Posts: 8338
Joined: Tue Oct 29, 2002 5:28 am
Location: Seven Kings, London UK
Contact:

Post by Bhikkhu Pesala » Sat Jun 14, 2008 7:47 pm

Ligature ct is discretionary, ff and so on are standard ligatures.
My FontsReviews: MainTypeFont CreatorHelpFC12 Pro + MT9.0 @ Win10 1903 build 18362.295

William
Top Typographer
Top Typographer
Posts: 1994
Joined: Tue Sep 14, 2004 6:41 pm
Location: Worcestershire, England
Contact:

Post by William » Mon Jun 16, 2008 6:22 am

Bhikkhu Pesala wrote:Ligature ct is discretionary, ff and so on are standard ligatures.
Yes, the ct ligature is discretionary. A given font need not implement a ct ligature at all.

However, I am thinking of the situation, (which may well never be used by most people, yet which may be of much interest to some specialist users), where a plaintext file contains a transcription of an old printed book where the usages of ligatures in the original printed book are specifically recorded in the plaintext file. If the c ZWJ t sequence is not included in the glyph substitution table as a standard ligature, then the c ZWJ t would be rendered as ct without the use of a ligature glyph: in fact, the direct opposite of what is desired.

Certainly, this is a special situation, just as a font having several long s ligature glyphs is a special situation. Indeed, having several long s ligature glyphs each with direct ligation and ZWJ ligation situations included within the glyph substitution rules of the font would be a quite specialized font. However, a font which has all of those facilities would be a special font, perhaps widely noted and referenced for its facilities.

There is a section about Cursive Connection and Ligatures in the following pdf, from the lower part of page 8 to the lower part of page 12 of the pdf.

http://www.unicode.org/versions/Unicode5.0.0/ch16.pdf

There is also a section about Latin Ligatures: U+FB00–U+FB06 in the following pdf, in the lower part of page 14 of the pdf.

http://www.unicode.org/versions/Unicode5.0.0/ch07.pdf

Both of those pdfs and other chapters of The Unicode Standard are available from the following page.

William Overington

16 June 2008

dejudicibus
Posts: 1
Joined: Thu Aug 08, 2019 1:33 pm

Re: ct ligature

Post by dejudicibus » Thu Aug 08, 2019 10:38 pm

CT ligature is VERY common in latin documents. So I am used to simulate a «Latin Small Ligature CT» by a «Latin Small Letter C with Hook» plus a «Latin Small Letter T», that is, ƈt.

Post Reply