Tested that Format0 works with Kannada MN font:
$ make -j5 lib -s && HB_OPTIONS=aat ./hb-shape Kannada\ MN.ttc -u 0C95,0CC2
[kn_ka=0+1000|kn_matra_uu=0@-30,0+1345]
$ make -j5 lib -s && HB_OPTIONS=aat ./hb-shape Kannada\ MN.ttc -u 0C95,0CC2 --features=-kern
[kn_ka=0+1030|kn_matra_uu=0+1375]
Note that GPOS does the same with 'dist' feature, and applies the whole difference to the
same glyph:
$ make -j5 lib -s && ./hb-shape Kannada\ MN.ttc -u 0C95,0CC2
[kn_ka=0+970|kn_matra_uu=0+1375]
$ make -j5 lib -s && ./hb-shape Kannada\ MN.ttc -u 0C95,0CC2 --features=-dist
[kn_ka=0+1030|kn_matra_uu=0+1375]
Makes our FT-backed hb_font_t safe to use from multiple threads. Still,
the underlying FT_Face should NOT be used from other threads by client
or other libraries.
Maybe I add a lock()/unlock() public API ala PangoFT2 and cairo-ft.
Maybe not.
Now that we have get_h_advances() and get_nominal_glyphs() implemented, the
overhead of doing a proper atomic load would be once per run, NOT once per
glyph. So, no need to pre-load the tables to avoid that overhead.
As such, hb_ot_font_set_funcs() has become really cheap. Can *finally* make
it be default font functions on all newly created fonts!
Some more measurable speedup. The recent commits' speedups are as follows:
Testing with Roboto, ****when disabling kern and liga****:
Before:
FT --features=-kern,-liga
user↦ 0m0.521s
OT --features=-liga,-kern
user↦ 0m0.568s
After:
FT --features=-liga,-kern
user↦ 0m0.428s
OT --features=-liga,-kern
user↦ 0m0.470s
So, 17% speedup.
Note that FT callbacks are faster than OT these days since we added an advance
cache to FT. I don't think the difference is enough to justify adding a cache
to OT.
When not disabling kern, the thing is three times slower, so the speedups
are three times less impressive... Still, 5% not bad for a codebase that I
otherwise thought is optimized out.
Note that, because of this and other optimiztions in our main shaper,
disabling kern and liga, the OT shaper is now *faster* than the fallback
shaper. So, that's my recommendation to clients that need the absolute
fastest...
Behdad Esfahbod
Ebrahim Byagowi
Michiharu Ariza