On Tue, Dec 18, 2018 at 11:43 AM Nikolaus Waxweiler <madig...@gmail.com> wrote:
> Thanks Alexei for chiming in at > https://github.com/googlei18n/fontmake/issues/492#issuecomment-448249543. > > > The following seems to be different: hhea does not seem to be used in > VF. Compare and decide which one is correct. > > > > > https://git.savannah.gnu.org/cgit/freetype/freetype2.git/tree/src/truetype/ttgxvar.c#n1365 > > > https://git.savannah.gnu.org/cgit/freetype/freetype2.git/tree/src/sfnt/sfobjs.c#n1670 > > The OpenType spec says nothing variation specific about hhea/typo/win > metrics, except that hhea vmetrics don't seem to be supported by the > `MVAR` in that only win and typo metrics have `MVAR` tags: > The reasoning for that was that varfonts should set OS/2 useTypoMetrics bit on and as such only one set of values need variation. I would say if that bit is off then the respective MVAR tags should be applied to hhea values. > - > https://docs.microsoft.com/en-us/typography/opentype/spec/hhea#39hhea39-table-and-opentype-font-variations > - > https://docs.microsoft.com/en-us/typography/opentype/spec/mvar#value-tags > - > https://docs.microsoft.com/en-us/typography/opentype/spec/os2#stypoascender > - > https://docs.microsoft.com/en-us/typography/opentype/spec/os2#uswinascent > > Regarding ascender, descender and height calculation in sfobjs.c and > ttgxvar.c: the math seems to be the same: > > - hhea: ascender 983, descender -217, line gap 0 -> total height 1200 fU > - typo: ascender 739, descender -217, line gap 244 -> total height 1200 fU > - win: ascender 983, descender 217, line gap 0 -> total height 1200 fU > > For static fonts, FT uses hhea metrics: `root->height = root->ascender > - root->descender + face->horizontal.Line_Gap;` or `983 - (- 217) + 0 > = 1200` > For instances, it uses typo metrics: `root->height = root->ascender - > root->descender + face->os2.sTypoLineGap;` or `739 - (-217) + 244 = > 1200` > > Will look into this deeper later. > > _______________________________________________ > Freetype-devel mailing list > Freetype-devel@nongnu.org > https://lists.nongnu.org/mailman/listinfo/freetype-devel > -- behdad http://behdad.org/
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