Re: [ft-devel] FT_Get_PS_Font_Private in CFF driver

[Werner LEMBERG]

> 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