[HarfBuzz] difference between harfbuzz and uniscribe?

[Martin Hosken]

Dear Behdad,

Some pertinent further information and that is that both diacritics were previously attached to the base before these rules are applied.

> Consider a font with the following FEA rule in it:
> 
> pos u1014' 79 u1032 u1037;
> 
> which adds 79 to the advance of the first glyph in the sequence u1014 u1032 u1037:
> 
> [u1014=0+609|u1032=0 at -89,-42+0|u1037=0 at -55,0+0]
> 
> vs without the 1037:
> 
> [u1014=0+530|u1032=0 at -10,-42+0]
> 
> But if we compare with a recent uniscribe we get:
> 
> [u1014=0+609|u1032=1 at -10,-42+0|u1037=2 at 24,0+0]
> [u1014=0+530|u1032=1 at -10,-42+0]
> 
> and if we change the rule to compensate for the advance in the windows case we get:
> 
> pos u1014' 79 u1032' <-79 0 0 0> u1037;
> 
> harfbuzz gives:
> 
> [u1014=0+609|u1032=0 at -168,-42+0|u1037=0 at -55,0+0]
> [u1014=0+530|u1032=0 at -10,-42+0]
> 
> uniscribe gives:
> 
> [u1014=0+609|u1032=1 at -89,-42+0|u1037=2 at 24,0+0]
> [u1014=0+530|u1032=1 at -10,-42+0]
> 
> Yours,
> Martin