bug#39554: 27.0.50; cairo not composing sequences

[Robert Pluim]

>>>>> On Thu, 13 Feb 2020 23:50:51 -0500, James Cloos <cloos@jhcloos.com> said:

>>>>> "YM" == YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp> writes:
    YM> I guess the difference comes from with vs. without HarfBuzz rather
    YM> than cairo vs. xft.

    James> makes sense.

    YM> Could you check if that is the case on your environment?

    James> all i know is that w/o cairo, describe-char reports:

    James>     xft:-unknown-DejaVu Sans 
Mono-normal-normal-normal-*-22-*-*-*-m-0-iso10646-1
    James> by these glyphs:
    James>   [0 1 48 19 13 0 13 17 1 nil]
    James>   [0 1 824 704 0 0 13 17 1 [-13 0 0]]

Thatʼs XFT not using harfbuzz

    James> and w/ cairo it reports:

    James>     ftcrhb:-unknown-DejaVu 
Serif-normal-normal-normal-*-22-*-*-*-*-0-iso10646-1
    James> by these glyphs:
    James>   [0 1 48 19 14 1 12 16 0 nil]
    James>   [0 1 824 741 0 -17 -1 18 1 nil]

And this is Cairo using harfbuzz.

    James> I presume that the '0 0 13 17 1 [-13 0 0]' vs '0 -17 -1 18 1 nil'
    James> represents the failed overlay.

    James> and that ftcrhb expands to freetype-cairo-harfbuzz.

    James> it is a pain to dig deep w/o the left hand, but i can try w/ some
    James> leading suggestions.  i haven't looked at the src since before my 
last
    James> stroke, much less since this one.

I donʼt see the issue with DejaVu Sans Mono in an Xft build, and
can reproduce it in an Xft+Harfbuzz build, so Cairo is not to blame
here.

Robert