[MPEG-OTSPEC] Font metrics for writing systems other than Western and CJK (was RE: AHG Kick-off ...)

[Levantovsky, Vladimir]

On Wednesday, March 25, 2020 4:27 PM John Hudson wrote:

On 25032020 12:56 pm, Levantovsky, Vladimir via mpeg-otspec wrote:

1.       Lack of font metrics for writing systems other than Western and CJK
Additional discussions are needed, we may need to consult with outside experts who are familiar with typographic environments of different languages and writing systems to consider the additional complexities associated with languages like Thai [where glyphs are often composed with multiple marks positioned above and below the base].

There are a couple of components to this:

1) Script- or language-specific versions of common metrics used for linespacing.

2) Script-specific data points that define internal relationships (in the way, e.g. cap height, x-height, ascender, and descender data points define height relationships in European scripts).

There has been a lot of prior discussion in the OTWG on (1), and the consensus seems to be that this should be done with a new version of the BASE table, using existing OTL script and language system tags with sets of vertical metrics for linespacing corresponding to the OS/2 table Typo metrics.

(2) has been discussed in various places, but as you say consultation is needed to identify the data points that are useful for each script (which might not always be obvious: much depends on how the data points might be used, e.g. in calculating size and alignment of 'dropcap' initials in CSS).

[VL] Thank you John,

As it relates to item 2), I am curious if some typographic tools used for certain scripts (drop caps in particular, as they are mentioned in CSS liaison as a use case "A") can be considered universally applicable for all scripts; or whether some of these tools (such as drop caps) are strictly a product of typographic norms and traditions that may be commonly used in some scripts but never in others.

Vladimir



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John Hudson

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