Re: RTL PUA?

On Mon, 22 Aug 2011 20:58:23 +0200
Philippe Verdy <verdy_p_at_wanadoo.fr> wrote:

> The computing order of features should not then be:
> - BiDi algorithm for reordering grapheme clusters
(I trust you mean the ordering of clusters relative to one another, not
the ordering within clusters.)
> - font search and font fallback (using cmap)
> - GSUB (lookups of ligatures or discretionary glyph variants)
> - GPOS
> but really:
> - font lookup and font fallback (using cmap)
> - GSUB (lookups of ligatures or discretionary glyph variants)
> - BiDi algorithm for reordering glyphs representing the grapheme
> clusters or ligatured grapheme clusters
> - GPOS

You've forgotten the conversion from encoding order to mechanical
typing order. That is done before GSUB, but needs some assistance from
GSUB for multipart characters (typically circumposed vowels).

> The BiDi algorithm absolutely does not have to be changed.

But you have to remember that preposed combining marks (and
fragments) must inherit the BiDi class of the base letter. I'm glad
you know what a circumposed Indic vowel looks like when subject to a
right-to-left override.

Richard.
Received on Tue Aug 23 2011 - 03:18:50 CDT