[HarfBuzz] Some optimizations

Tue Oct 16 15:02:49 PDT 2007

On Tue, 2007-10-16 at 03:22 -0400, Lars Knoll wrote:
> On Monday 15 October 2007, Behdad Esfahbod wrote:
> > Well, I went ahead and made some other changes that touched all over the
> > code:
> >
> >   - Removed FT_Memory cruft, using malloc/realloc/free directly.
> 
> I don't understand that. We have done that change in harfbuzz half a year ago 
> already in the master branch. See 
> http://gitweb.freedesktop.org/?p=harfbuzz.git;a=commitdiff;h=08bf1afd409c161321eacd5761582a02e3d823ee
> 
> Are you working against master or stable here?

Well, stable.  And that's the problem.  Simon's work on getting rid of
FreeType and adding Qt shapers was so interweaved that I had no chance
of updating to the cleanup bits without pulling in shapers until I get
to synching...

> >   - Marking harfbuzz-internal symbols HB_INTERNAL and define that
> > macro to static in harfbuzz.c, to help compiler do a better job.
> 
> That sounds like a valid and easy to apply patch.

Yep.  Shouldn't take more than 10 minutes to redo.  Just mark _HB_* with
it.

> > Also made some other cleanups and moved pango to building harfbuzz.c
> > instead of individual files.
> >
> > Anyway, seems like easiest way to deal with my changes is to wait until
> > I merge this new tree with my harfbuzz-ng rewrite tree and make that the
> > harfbuzz of future.
> >
> > In the mean time, I'm attaching the two real bugfixes here.  This should
> > be of interest to Qt.  Just pushed them in pango-1-18 branch too.
> 
> Thanks. Simon is travelling this week, and I'm also pretty tied up, but we'll 
> try to merge this and your last patch by next weeek.

Forget about the large patch I sent, just pick up the small patch that
fixes two bugs.  I'll get to grand-merging with Simon's work (master)
when I make some progress with mmap()ed tables (merging is starting to
look like a huge task btw, looking at gitk --all now).

Thanks,
behdad

> Cheers,
> Lars
> 
> > Summary:
> >
> > 2007-10-15  Behdad Esfahbod  <behdad at gnome.org>
> >
> >         * pango/opentype/harfbuzz-open.c (Load_ClassDef2),
> >         (_HB_OPEN_Load_Device): Two small bug fixes backported
> >         from trunk.  Namely: skip bad ClassDef2 entries and
> >         skip invalid DeltaFormat device tables.  Makes Nafees
> >         Nastaliq font work great, and avoids warnings with
> >         some other fonts.
> >
> >
> >
> > Regards,
> >
> > behdad
> >
> > On Wed, 2007-10-10 at 20:33 -0400, Behdad Esfahbod wrote:
> > > Hi,
> > >
> > > For Boston Summit this year I sat down optimizing harfbuzz buffer a bit
> > > to avoid unnecessary copy/swap'ing when glyphs do not change.  The idea
> > > is to use the same string for in and out, essentially working in-place,
> > > until a change that doesn't fit in-place is needed at which point we
> > > lazily create a separate out buffer and copy over.
> > >
> > > Unfortunately I didn't start this in a git-svn pango checkout and ended
> > > up piling changes on top of each other.
> > >
> > > Around the final round it was about 1700 lines worth of diff, but to
> > > find why a particular Invalid_SubTable error was being hit I needed to
> > > see where the error is originating from, so I renamed remaining FT_Err
> > > instances to HB_Err and made the entire code call _hb_err() when
> > > returning an original error, so you can set a breakpoint on it.  It
> > > helped debugging the bug in a minute, but also means that the patch is
> > > over 7000 lines now :(.  Sorry Simon :(.
> > >
> > > Anyway, it's here:
> > >
> > >   http://bugzilla.gnome.org/show_bug.cgi?id=485559
> > >
> > > Quick summary:
> > >
> > > 2007-10-10  Behdad Esfahbod  <behdad at gnome.org>
> > >
> > >         Bug 485559 – Boston Summit HarfBuzz optimizations
> > >
> > >         * pango/opentype/*: HarfBuzz hacking to:
> > >
> > >           - Rename last remaining FT_Err stuff to HB_Err.
> > >
> > >           - Fix a couple invalid table paths to be permissive so
> > >             fonts work better.  Particularly GDEF table for Nafees
> > >             Nastaliq is loaded and works great now.
> > >
> > >           - Optimize harfbuzz buffer to not copy/swap for simple
> > >           one-to-one and "copy" GSUB operations.
> > >
> > >         * pango/pango-ot*: Update to FT_Err to HB_Err renaming.
> > >
> > >
> > > I think the easiest way to apply it to harfbuzz upstream is to rip out
> > > the FT_Err and _hb_err changes out, apply it, and redo them...  I'll
> > > give it a try if it's too much pain for Simon to do (which I totally
> > > understand if it is), but other than that, it can use a pair of eyes.
> > > Specially the harfbuzz-buffer changes.
> > >
> > > Tomorrow I'll make pango cache a single harfbuzz buffer instead of
> > > recreating them all the time.
> > >
> > > A very warm feeling of doing this all is that I feel much more
> > > comfortable with the GSUB code now.  GPOS still has a bit of mystery to
> > > discover.  All in all quite good just in time for picking up the rewrite
> > > again, which I'm starting next week.
> > >
> > > Regards,
> 
> 
> _______________________________________________
> HarfBuzz mailing list
> HarfBuzz at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/harfbuzz
-- 
behdad
http://behdad.org/

"Those who would give up Essential Liberty to purchase a little
 Temporary Safety, deserve neither Liberty nor Safety."
        -- Benjamin Franklin, 1759