[OpenType] ReqFeatureIndex: obsolete?

[Sairus Patel]

I'd like to work on a formal proposal to deprecate ReqFeatureIndex. This is a preliminary call for concerns.

The wording would be something like: "This field has been deprecated as of OT 1.x. Fonts should set its value to 0xFFFF." Stronger wording may be warranted, depending on how this "call for concerns" plays out.

As stated in my previous message below, it doesn't make sense to keep this facility since a different and incompatible scheme for "required features" was later introduced: the OT layout specifications at http://www.microsoft.com/typography/SpecificationsOverview.mspx ("Script-specific Development" section). These specifications indicate certain standard features as required or not; e.g. the 'fina', 'medi', and 'init' features are required to be applied for Arabic layout (http://www.microsoft.com/typography/otfntdev/arabicot/features.aspx). 

These are incompatible schemes since, to quote from my message below:

"[ReqFeatureIndex] doesn't make sense in a layout model wherein features are to be applied one at a time, as in MS' Arabic layout spec -- should the required feature be applied every time one of the features is applied, or only once? If once, when? Before the other features, after them, or at some other point?"

If we support the layout specs model then we should be deprecating ReqFeatureIndex, or at least clarifying when ReqFeatureIndex should be applied if we really want to keep this facility.

So, as a start, please speak up if you think ReqFeatureIndex should not be deprecated.

Thanks!

Sairus



-----Original Message-----
From: listmaster at indx.co.uk [mailto:listmaster at indx.co.uk] On Behalf Of Sairus Patel 
Sent: Wednesday, July 21, 2010 4:39 PM
To: multiple recipients of OpenType - sent by
Subject: RE: [OpenType] ReqFeatureIndex: obsolete?

Message from OpenType list:


I'd like to see ReqFeatureIndex declared deprecated/obsolete as well.

Adobe's CoolType font engine removed support for it in 2005, and FTE (Flash Text Engine) has never supported it. It doesn't make sense in a layout model wherein features are to be applied one at a time, as in MS' Arabic layout spec -- should the required feature be applied every time one of the features is applied, or only once? If once, when? Before the other features, after them, or at some other point?

It is present in a few XP and Office XP fonts:

* Arial (Regular and Bold) version 3.00 and Times New Roman (Regular and Bold) version 3.00 These use the required feature for Arabic layout, and it points to the 'rlig' feature.

* Arial Unicode MS (Regular), versions 1.00 and 1.01 These use the required feature for Kannada layout, and it points to a 'requ' feature which raises the ASCII range punctuation (! , . : ; ?) by 200 units.

* Palatino Linotype (all 4 Windows styles), various versions These use the required feature under the Romanian language system (latn/ROM), and it points to the 'liga' feature.

My records indicate that MS had confirmed with me that ReqFeatureIndex would not be used for these fonts when they were updated for Vista.

The advantage of indicating such a facility as deprecated or obsolete in the spec is that newer layout engines may have more justification if they choose not to implement them. That said, OT doesn't have a clear definition of what "deprecated" or "obsolete" means.

Sairus
	
-----Original Message-----
From: listmaster at indx.co.uk [mailto:listmaster at indx.co.uk] On Behalf Of Adam Twardoch (List)
Sent: Wednesday, July 21, 2010 4:00 AM
To: multiple recipients of OpenType - sent by
Subject: [OpenType] ReqFeatureIndex: obsolete?

Message from OpenType list:


 Dear list members,

one aspect of OpenType that has been bugging me for some time is ReqFeatureIndex [1].

Has this been ever implemented in any major fonts and/or layout engines?

I am under the impression that this mechanism has not been used, and that it has been de facto superseded by "locl". In such case, wouldn't it make sense to declare it obsolete, or remove it?

Best,
Adam

[1] http://www.microsoft.com/typography/otspec/chapter2.htm
-- section " Language System Table"


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