Hi Richard, On 15/10/18 6:53 pm, Richard Wordingham via Unicode wrote: > On Mon, 15 Oct 2018 01:55:24 +1100 > Harshula via Unicode <unicode@unicode.org> wrote: > >> 3) However, what you have observed is an issue with *explicit* >> conjunct creation. After the segmentation is completed, the >> layout/shaping engine needs to first check if there is a >> corresponding lookup for the explicit conjunct, if not, then it needs >> to remove the ZWJ and redo the segmentation and lookup(s). Perhaps >> that is not happening in Harfbuzz. > > This indeed seems to be the problem with HarfBuzz and with Windows 7 > Uniscribe. Curiously, they almost adopt this behaviour when touching > letters are not available. (The ZWJ seems not to be completely removed > - in HarfBuzz at least it can result in the al-lakuna not interacting > properly with the base character.) > > But where is this usually useful behaviour specified? > > 1. There may be nothing but time and money to stop fallbacks being > built into the font. For example, what prohibits the rendering of a > conjunct falling back to touching letters or a missing glyph symbol?
I had not considered the missing glyph symbol. Perhaps that is the most accurate solution when a font is missing a glyph during an *explicit* conjunct lookup. Note, touching letters are formed by <ZWJ><AL-LAKUNA>, so they should not be displayed as a fallback for <AL-LAKUNA><ZWJ> conjuncts. cya, #