[Fontconfig] kerning improvements

[Owen Taylor]

On Fri, 2003-09-05 at 00:32, David Chester wrote:
> Hello, 
>   
>  I have a submitted a patch to freetype which improves kerning in the 
>  autohinter.  Here are my posts on freetype's devel list: 
>   
>  http://www.freetype.org/pipermail/devel/2003-July/009545.html
> http://www.freetype.org/pipermail/devel/2003-July/009559.html
>   
>  At this time the McGill site which hosts the example images seems to be 
>  down, but I put up the second graphic at: 
>   
>  http://chesterandvestal.ath.cx:8000/kern2.png
>   
>  Basically, errors from rounding the advance widths are remembered and 
>  accounted for during layout, one level up (i.e. in Xft or ftstring, etc.).
>  In the 
>  posts above, I attached a patch which makes ftstring (from the ft2demos 
>  package) able to take these errors into account.  However, I am unfamiliar
> with 
>  the Xft code, and I am wondering how this might be implemented in Xft.     
>   
>  The patch has not yet been accepted, and it may eventually have a very 
>  different implementation in the end, but it would be useful to know exactly
> how 
>  this would work with Xft. 

I've fooled around a bit with similar things for Pango recently - see
the draft of a writeup at:

 http://people.redhat.com/otaylor/grid-fitting/ 

In particular the section called "Reducing the deviation: grid-fit
kerning".

I didn't modify FreeType for the experiments I did there, but simply
figured out the side-bearing errors by comparing the unhinted outline
bounding box and metrics to the hinted outline bounding box and 
metrics.

When you get an API into FreeType, making Pango support it will be 
pretty easy; Xft support wont be necessary, since Pango does all 
glyph positioning itself and just feeds Xft the positioned string.

Regards,
						Owen