Are device metrics tables still required?

Malcolm Wooden

I have stopped adding 'hdmx' and 'LTSH' to hinted ttf's but I still add 'VDMX'. Is this table still required, even for OTVars?

John Hudson

VDMX is slightly different from the other cached device metrics tables in that it is sometimes used to actually delta the vertical ppem metric space, i.e. to set the available pixel body height to be different from the calculated value. But if the values in the VDMX table do equal the calculated value, then I would say that you don't need the table, because there's no significant performance benefit to caching the metrics any more.

We've got some fonts we maintain for Microsoft in which we're obliged to keep the VDMX table because it deltas some sizes — notably for UI fonts, to reduce the pixel height at small sizes —, but other than that we don't bother with any of the cached metrics tables any more.

Malcolm Wooden

Thank you for the information John.