Re: Layout-dependent feature subsetting

Yes, exactly. The IFT client would be expected to include the list of
discretionary features which it's shaping engine is expected to need in the
request in addition to any content requested layout features (eg. specified
via css).

On Tue, Jun 6, 2023 at 2:39 PM John Hudson <john@tiro.ca> wrote:

> Skef wrote:
>
> With respect to layout features, IFT sits in the overall font stack at the
> same level as a shaper. That is, you tell the "client-side IFT subsystem"
> what you need using parameters analogous to how you tell your shaper what
> you need.
>
> So in your case, it seems (and correct me if I'm wrong) that whatever
> higher-level layout settings may be at issue, at some point you're going to
> feed codepoints into your shaper with the rtla and/or rtlm features active
> (or if you have a more custom shaper do something equivalent, such that it
> will wind up digging around in the lookups indicated by those tags).
> Therefore your overall system must be "rtla/rtlm 'aware'" in at least that
> sense.
>
> That makes sense. So the expectation is that the client will be passing
> all the discretionary layout features applied to the text, regardless of
> whether they have been applied by the user or by whatever process is
> handling text arrangement.
>
> Would be a good idea to make some test cases around this for CJK and bidi
> related layout-dependent features.
>
> J.
>
>
> --
>
> John Hudson
> Tiro Typeworks Ltd    www.tiro.com
>
> Tiro Typeworks is physically located on islands
> in the Salish Sea, on the traditional territory
> of the Snuneymuxw and Penelakut First Nations.
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