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Re: advanced font features in CSS

From: Tal Leming <tal@typesupply.com>
Date: Tue, 30 Jun 2009 08:18:14 -0400
Cc: Christopher Slye <cslye@adobe.com>
Message-Id: <9392CA1D-CF3B-4B75-9709-1B0B7E1F216D@typesupply.com>
To: www-style <www-style@w3.org>

On Jun 30, 2009, at 2:46 AM, Christopher Slye wrote:

>> Contextual ligatures (clig) may be better grouped with ligatures.  
>> Most
>> applications group these along with liga under a generic "Ligatures"
>> option.
>
> I don't personally see any reason to separate 'calt' and 'clig'.

Think of this case:

	font-variant-ligatures: no-common-ligs no-additional-ligs no- 
historical-ligs;
	font-variant-alternates: contextual;

This user is trying to deactivate all ligatures and activate  
contextual alternates. If calt and clig are grouped together the user  
still gets ligatures.


>>> swash: swsh(number), cswh(number) (OT), AAT?
>>
>> As Thomas mentioned, most fonts use contextual forward and backward
>> tracking to automatically insert the proper swash. In fact, I don't
>> know that I've ever seen a font that uses GSUB lookup type 3 as the
>> spec describes for swashes. I think it may be safer to allow users to
>> activate swashes independent of a specific number.
>
> I wouldn't be surprised if we have a 'swsh' feature in our library  
> somewhere that uses LookupType 3. The 'swsh' feature has a sloppy  
> history: It has sometimes been used as something like a stylistic  
> set, meant to be activated all at once; it has been used as a simple  
> alternate substitution, intended to be used discretely (only); and I  
> think it has been done as a one-from-many substitution and as a  
> contextual substitution. (This is speaking of the Adobe Type  
> Library. I'm not sure what everyone else is doing.) It's hard to  
> predict how it's going to be, I think.

Hm. I still think that if access to specific alternates is desired,  
aalt is a better place to do it.


>>> alternates: salt(number) (OT), character alternatives = number (AAT)
>>
>> This is the same as the swsh(number) problem mentioned above. The  
>> salt
>> implementation has been an area of debate for a long time.
>
> Has it? I'm not aware of any long running debate. We customarily  
> implement it as a LookupType 1 and LookupType 3. Either way, it's  
> intended as a user-selected, discretionary feature. Or are you  
> talking about how 'salt' is activated in the user interface? Yes,  
> that is debatable. :)

Yes. That is what I mean.

Tal
Received on Tuesday, 30 June 2009 12:19:03 GMT

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