[MPEG-OTSPEC] On condvalue_spec.pdf

[Skef Iterum]

On 4/23/24 11:43, Behdad Esfahbod wrote:
> Hi Skef,
>
> I'm implementing the ConditionValue proposal, and have some feedback. 
> This is based on the following document:
> units
> https://github.com/adobe-type-tools/opentype-spec-drafts/blob/main/condvalue_spec.md
>
> """
> In "FeatureVariations Table", note that if minorVersion is 0 then only 
> Condition Table version 1 can be used. If minorVersion is 1 then 
> Condition Table version 2 can also be used.
> """
> I highly suggest removing this. The minorVersion is for when new 
> fields are added to FeatureVariations table itself. It should not be 
> relied on for anything else.
>
That can be a solid suggestion for a future change. The proposals are in 
now.

The thought was to try to discourage fonts that would look like they were
compatible with the previous spec but contained new condition format types,
but I suppose it doesn't really accomplish that anyway.

Note that the existing (pre-working draft) Open Font Format specification
screwed up the advice of what to do when a new condition format is added,
referring to the version of a condition set, which doesn't exist. 
Therefore we
don't really know what implementations will do when they encounter new
condition types. The two obvious choices are "ignore" and "treat the 
condition
set containing the condition as not applying, but unfortunately those are
quite different.

> """
> Add new subpart between "Condition Table Format 1: Font Variation Axis 
> Range" and "FeatureTableSubstitution Table" with this content:
> """
> Can we name Format1 simply ConditionAxisRange? That would go better 
> with ConditionValue, ConditionAnd, ConditionOr, and ConditionNegate.
>
I recall seeing this in a recent draft of your proposal, so presumably that
will happen. Seems fine to me.
> """
> On page 166: "Within the GPOS, JSTF, GDEF and BASE tables, delta-set 
> indices are stored in VariationIndex tables."
> """
> I don't understand this. What is a VariationIndex table?
>
That's, I believe, section 6.2.8 or alternatively 
https://learn.microsoft.com/en-us/typography/opentype/spec/chapter2#device-and-variationindex-tables 
(scroll down a bit from this anchor). But I'm not sure how that would be 
relevant to what you're currently implementing.

Skef


> Thanks,
>
> behdad
> http://behdad.org/
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