[MPEG-OTSPEC] 'opbd' feature

[Peter Constable]

Thanks, John

As part of a separate issue that required touching the "Application interface" fields, I've drafted a revision for 'lfbd' and 'rtbd' to say the following:

"In recommended usage, the application applies this feature automatically to characters at the right end of a horizontal line when the 'opbd' feature has been applied to those characters. See the the ['opbd'](#opbd) feature for additional information."

To allow for usage of 'lfbd' or 'rtbd' independent of 'opbd', I've have to revise that, but that would be doable.


Peter

From: mpeg-otspec <mpeg-otspec-bounces at lists.aau.at> On Behalf Of John Hudson
Sent: Wednesday, September 16, 2020 3:02 PM
To: MPEG OT Spec list (mpeg-otspec at lists.aau.at) <mpeg-otspec at lists.aau.at>
Subject: Re: [MPEG-OTSPEC] 'opbd' feature

On 16092020 2:50 pm, Peter Constable wrote:
Since Adobe had registered this feature, I asked them to investigate and come up with a recommendation. Sairus has just provided Adobe's recommendation in the issue discussion:
 "Adobe would like 'opbd' and its minions 'lfbd' & 'rtbd' to be marked as deprecated in the features registry."
 I'd like to hear from others if they would support or, at least, have no objection to these being marked as deprecated.

I am 100% okay with opbd being deprecated.

The individual lfbd and rtbd features are, however, potentially useful without opbd if rewritten and, indeed, could constitute part of a model that might also involve tpbd (top) and (btbd) bottom optical bounds features for vertical text. The error of the original feature registration was the idea that a single feature was needed to be able to apply the others, as a kind of gateway between application function and the individual features and their lookups. The idea of using GPOS to define margin alignment isn't a terrible one in itself, especially for some scripts and styles that are not well served by algorithmic margin alignment such as currently available in InDesign.

That said, implementation of GPOS optical margin alignment, in both fonts and applications, requires some significant work, which I'm not holding my breath awaiting. I would rather, however, consider these features potential or pending, rather than deprecated. It would be silly to formally deprecate them and then decide down the road that we'd actually like to use them.

JH



--



John Hudson

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