Re: [ft-devel] FT_Get_PS_Font_Private in CFF driver

[Michael Toftdal]

Hi Werner,

Okay, so in my specific case (CFF) the value is not used.

I have been busy with other things, and was about to start making the change in 
the FreeType code that we talked about. But it's a little demotivating that the 
(required!) value is not used anyway...

Thanks a lot for forwarding the Adobe communication though.

Regards,
Michael


On 01/06/2013, at 14.48, Werner LEMBERG wrote:

> 
>> BTW, I've already received a `This is a good question' answer from
>> Adobe, waiting for more to come :-)
> 
> And here it is.  The answer is far from trivial...
> 
> Dave Arnold says that there are two cases where the StemV value is
> used (he wrote that from memory):
> 
>  . to select a font weight if a font substitution happens
> 
>  . to guide stem darkening for embedded TrueType fonts.
> 
> Note that Adobe uses a special, self-made version of the TT
> interpreter which both handles stem darkening and artificial
> emboldening *before* hinting takes place.
> 
> The StemV value is *not* used by the PDF engine if the embedded font
> is either a Type 1 or CFF font; in that case the value from the
> private dictionary gets used.  For a CID font, the value associated
> with the glyph's font DICT gets used.
> 
> In case there is no StemV value in the PDF, the following algorithm
> applies:
> 
>  . use a heuristic method to measure a particular glyph outline for
>    getting a proper value
> 
>  . if that fails, use a default value (Dave believes it's 75 units)
> 
> Similarly, this default value is used for CFFs which miss a StdVW
> operator.
> 
> 
>    Werner