[HarfBuzz] OpenType features in ScriptShape/PlaceOpenType

[Andrew Glass (WINDOWS)]

Hi Behdad,



The required features are marked in the published specifications where applicable. For example:


Feature

Feature function

Layout operation

Required

Language based forms:





ccmp

Character composition/decomposition substitution

GSUB



Typographical forms:





liga

Standard ligature substitution

GSUB



clig

Contextual ligature substitution

GSUB



Positioning features:





kern

Pair kerning

GPOS



mark

Mark to base positioning

GPOS

X

mkmk

Mark to mark positioning

GPOS

X






During Win 8, we added <dist> to the list of required features. Your question has made me realize that I need to update this document.



Note that not all of our engines currently accept custom feature lists. I’m currently working on updating our documentation in this area, and will make sure that specification of all of the required features is up to date.



Cheers,



Andrew



-----Original Message-----
From: Behdad Esfahbod [mailto:behdad.esfahbod at gmail.com] On Behalf Of Behdad Esfahbod
Sent: Friday, August 9, 2013 8:53 AM
To: Andrew Glass (WINDOWS)
Cc: Peter Constable; Harfbuzz
Subject: Re: OpenType features in ScriptShape/PlaceOpenType



Thanks Andrew.  That's what I suspected.  Can you please clarify which features are considered non-required?  Is that exactly kern, liga, clig, and calt?



Cheers,

behdad



On 13-08-09 11:50 AM, Andrew Glass (WINDOWS) wrote:

> Hi Behdad,

>

> Yes, this is the design. If a caller passes a list specifying features they wish to have applied, the need to specify all non-required features. For example, if they want to turn off kern and add tnum they just pass the set of optional features that they want to have applied.

>

> Cheers,

>

> Andrew

>

> -----Original Message-----

> From: Behdad Esfahbod [mailto:behdad.esfahbod at gmail.com] On Behalf Of

> Behdad Esfahbod

> Sent: Friday, August 9, 2013 6:45 AM

> To: Andrew Glass (WINDOWS)

> Cc: Peter Constable; Harfbuzz

> Subject: OpenType features in ScriptShape/PlaceOpenType

>

> Hi Andrew,

>

> Is it intentional that specifying any features in ScriptShape/PlaceOpenType disables kern, calt, clig, liga?

>

> Thanks,

> --

> behdad

> http://behdad.org/

>



--

behdad

http://behdad.org/


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