[XeTeX] Font protrusion --- new or old ?

[Jonathan Kew]

On 9 Feb 2009, at 00:19, Nicolas Vaughan wrote:

> @ Jonathan,
> Why do you say ---as you have been quoted--- that font protrusion  
> could be supported as an OpenType feature, and not directly through  
> the XeTeX engine?

Doing a good job of font protrusion requires per-glyph metrics that  
specify how much to adjust the sidebearings at line edges. As there  
are already opentype features defined for exactly this information,  
that's how it should be provided. I don't want to duplicate  
information in a custom, xetex-specific form when there is already a  
standard defined for it.

However, there would *also* need to be modifications to the xetex  
engine, as it does not currently have any support for automatically  
applying these features only in the appropriate places.

It's also true that people will want to be able to have protrusion  
even with fonts that don't provide optical bounds features, so that  
would mean having some alternative way to specify the protrusion data.  
But I don't want to simply do something "private" within xetex and  
ignore the relevant opentype specification.

(Adam T, are you listening? Do you know of any "pro" fonts that  
actually support opbd, or has this not actually be implemented  
anywhere?)

JK