Re: [css-text] Arabic letters connecting between elements with display: inline

On Fri, May 23, 2014 at 2:09 AM, Behdad Esfahbod <behdad@behdad.org> wrote:

>
> I disagree.  Joining should NOT be broken even if font changes.  Using a
> bold
> font to highlight a letter in print is a valid use.  It's hard.  But the
> alternative is wrong.  Whether user uses a different font weight or a
> different color to highlight shouldn't affect the correctness of the script
> behavior.
>

I am trying to understand what exactly joining across font changes means.

My conceptual model is that you have

a) script runs, consisting of characters with the same script and resolved
embedding level, which are broken into
b) font runs, consisting of characters with the same font and size

There are two parts to shaping:

(1) determining which joining form (and thus which GSUB features) to use
for each character
(2) applying GSUB/GPOS font features

My understanding is

- color should not affect how characters are split into either script or
font runs
- shaping (1) should be done as if applied to each script run independently
- shaping (2) should be done as if applied to each font run independently

Or are you suggesting doing shaping (2) on a font run should take into
account information from adjacent font runs?  If so, I don't understand how
that works.

James