hmtx optimzation for CFF should be allowed

Sairus Patel sppatel at
Wed Aug 15 20:12:47 CEST 2012

[Sending to both the OT and OFF lists.]

I'd like the following to be considered for inclusion in the 3rd OFF WD that's being worked on. It should be a simple, straightforward change.

If there are objections, please speak up.

==== Proposal

Remove the following sentence:

"OpenType fonts that include CFF data must set numberOfHMetrics equal to the number of glyphs in the font and therefore cannot use the "repeat last width" optimization normally available within the 'hmtx' table."

from the hmtx sub-section of the Recommendations section (OT; OFF sec 7).

==== Rationale:

There is no architectural reason to prohibit CFF OT fonts from availing of optimizations that are possible in OT tables that are shared with TT OT fonts, such as the hmtx table.

If any implementations impose such a limitation, they should be changed. However, Adobe has used this hmtx optimization in our CFF OT fonts since the beginning of OT, e.g. in CourierStd.otf, and we haven't heard of any problems with this.

Thus, we do not have any hesitations in proposing that the above restriction be removed from the Recommendations page.


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