HinTak/Font-Validator

Tables hdmx, VDMX, LTSH calculated by CacheTT.exe considered incorrect by FontVal

Opened this issue · 2 comments

madig commented
  1. cd /tmp && git clone --depth 1 https://github.com/daltonmaag/ubuntu.git && cd ubuntu && make # Install wine and curl first
  2. FontValidator.exe -file build/Ubuntu-R.ttf

FontVal will disagree on almost all entries of the hdmx, VDMX, LTSH tables, which have been calculated by CacheTT.exe. Not sure if FontVal or CacheTT are more correct?

HinTak commented

There are two aspects to matching the metrics returned from CacheTT.

  • the current implementation in FontVal is based on freetype; to what extent freetype matches what windows does.

  • to what extent CacheTT matches current microsoft windows.

(And there is the possibility of CacheTT being buggy also - it has not been updated for nearly 20 years AFAIK).

If the former is a problem, then it is a wider issue that freetype is not 100% windows-compatible metric-calculation wise.

As for the latter (and CacheTT being old...), I have occasionally wondered that since CacheTT was built before the millenium, and those metric tables perhaps were used in an era when computers were slower and caching metric calculation was necessary/desirable, it is more appropriate to use B/W rendering ( see #26 ). If you want to give #26 a go, please feel free to do so.

madig commented

FreeType not matching Windows is quite probable. I'd love to throw these tables out, but restaurating the Ubuntu font requires me to first match what's out there. Will try #26 when I get to it.