GNOME Bugzilla – Bug 654962
Please implement ligature features dlig, hlig
Last modified: 2012-08-25 19:19:44 UTC
Hi, The OpenType features with tables 'dlig' and 'hlig', as well as 'clig' would be very nice to see. They should be available to all scripts. They should be turned off by default, and turned on at the user's discretion. This should be pretty easy: otherwise 'dlig' and 'hlig' are just ligatures like 'liga' (which is turned on by default). The 'clig' feature is a reverse chaining substitution, which... I don't see that any of these are implemented yet in Pango. Maybe that's harder. See http://www.microsoft.com/typography/otspec/features_ae.htm The CSS3 Fonts Module Level 3 draft will allow web pages to refer to such features: http://dev.w3.org/csswg/css3-fonts/ Cheers!
Sorry, of course, 'clig' is alreday implemented. I added that at the last minute, and did the wrong search. The request for 'dlig' and 'hlig' remains.
These are all supported by harfbuzz already, but the Pango attributes to enable them are not there yet... In harfbuzz, I want to make a ZWJ character enable 'dlig' on its previous character.
Hi Behdad, I don't know if the behaviour you describe is standard. My understanding of the intent 'dlig' and 'hlig' is that they ought be be enabled somehow at the discretion of the user (via markup or an application command). The MS Layout Registry docs talk about these features "overriding" others, but I don't know quite what they mean by that, or how it would occur. But I would think that, if 'dlig' were turned on, it might somehow override the default ligature produced with a ZWJ. This doesn't sound like what you're proposing though.
*** This bug has been marked as a duplicate of bug 545510 ***