[HarfBuzz] Turning off ligatures and kerning

[Nikolay Sivov]

On 02.07.2016 2:11, Kelvin Ma wrote:
> How can I tell if a feature is enabled by default? Is it constant across
> scripts?

You can tell by looking at documentation, or source code. No, it's not
constant and depends on script/shaper used.

> And are feature values always True/False
> 

Already answered.

> On Fri, Jul 1, 2016 at 6:34 PM, Ebrahim Byagowi <ebraminio at gmail.com
> <mailto:ebraminio at gmail.com>> wrote:
> 
>     By passing a list of opentype features to harfbuzz, it just modifies
>     the default status of them but still has knows which ones should be
>     enabled or disabled in case user didn't explicitly set them.
> 
>     > Because i can turn off LIGA by passing a LIGA feature with value=0
>     and nothing will happen to arabic but CALT with value=1 changes it
>     In case of LIGA and CALT difference, that depends on that
>     specific font you are using whether it has marked which feature by
>     which tag. An identical stylic operation can have two different tag
>     on different fonts.
> 
>     On Sat, Jul 2, 2016 at 2:58 AM, Kelvin Ma <kelvinsthirteen at gmail.com
>     <mailto:kelvinsthirteen at gmail.com>> wrote:
> 
>         Now I’m even more confused, will harfbuzz override the features
>         in the features array if it’s setting arabic? Because i can turn
>         off LIGA by passing a LIGA feature with value=0 and nothing will
>         happen to arabic but CALT with value=1 changes it
> 
>         On Fri, Jul 1, 2016 at 6:24 PM, Ebrahim Byagowi
>         <ebraminio at gmail.com <mailto:ebraminio at gmail.com>> wrote:
> 
>             Different and essential operations of a shaper are divided
>             and marked by features and some features are enabled by
>             default per the specification, for example on Arabic
>             https://www.microsoft.com/typography/OpenTypeDev/arabic/intro.htm#features
> 
>             On Sat, Jul 2, 2016 at 2:33 AM, Kelvin Ma
>             <kelvinsthirteen at gmail.com
>             <mailto:kelvinsthirteen at gmail.com>> wrote:
> 
>                 && why does harfbuzz still use features if I pass it an
>                 empty list? How does it know whether to turn them on or off?
> 
>                 On Fri, Jul 1, 2016 at 6:02 PM, Kelvin Ma
>                 <kelvinsthirteen at gmail.com
>                 <mailto:kelvinsthirteen at gmail.com>> wrote:
> 
>                     So that’s what the value member does. thanks! Will
>                     it always be either 0 or 1?
>                     && what does .tag do?
> 
>                     On Fri, Jul 1, 2016 at 5:51 PM, Simon Cozens
>                     <simon at simon-cozens.org
>                     <mailto:simon at simon-cozens.org>> wrote:
> 
>                         On 02/07/2016 07:34, Kelvin Ma wrote:
>                         > So I think I figured out how to turn on font features, but how do I turn
>                         > ones off that are enabled by default? Like liga or kern?
> 
>                         Just set the value to 0 in the features array.
>                         See
>                         https://github.com/simoncozens/sile/blob/master/src/justenoughharfbuzz.c#L78
> 
>                         Simon
> 
> 
> 
> 
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