[HarfBuzz] Unified Text Layout Engine?

Rajeev J Sebastian rajeev.sebastian at gmail.com
Thu Feb 1 12:06:41 PST 2007

On 2/2/07, Eric Mader <emader at icu-project.org> wrote:
> Hi Behdad,
> The ICU LayoutEngine uses an abstract base class to represent fonts and
> so is independent of any particular font format or OS. (Though the model
> in the base class assumes that a font contains tables w/ four-byte
> names. ;-)
> I've thought for some time that the Indic shaper code in ICU is too
> fragile. When I wrote it, I though I could get away with a single
> routine to analyze and tag all Indic scripts. Since then, I've found out
> that there are lots of script-specific exceptions and it's sometimes
> hard to fix one script without breaking any of the others...
> A couple of years ago I talked w/ Owen Taylor about rewriting the code
> to have a (potentially) different shaper for each script. At that time I
> thought that almost all the bugs were fixed and it wasn't worth the
> effort. Subsequent experience has shown this belief to be optimistic. :-)
> As you probably know, Microsoft changed the spec. for Indic OpenType
> fonts for Vista. As soon as they publish the new spec. we'll  have to
> adapt our shaper to deal with the new fonts. I don't know all the
> details of what's required yet, but it looks like the shaper may have to
> "probe" the 'GSUB' table w/ trial lookups to determine, for example,
> which characters have pre- and post-base forms.

The model for some languages are changing as well. It is entirely
possible that Fallback Rendering will be removed for Malayalam and
perhaps other scripts or characters of scripts as well. So, the specs
may change yet again, and quite soon too.

Rajeev J Sebastian

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