[Devel] improved T1 hinting algorithm

[Werner LEMBERG]

I think that I've finally fixed the nasty bug which caused the jumping
(and sometimes bad hinting) of glyphs if the T1 hinter was active.

In pshalgo.c, there was a constant PSH_STRONG_THRESHOLD (set to 30)
which has been used to test whether a point becomes a `strong' point.
Regardless of the glyph's ppem value, always 30 font units have been
used as a threshold.  I've changed that.  PSH_STRONG_THRESHOLD now
holds the accepted shift for strong points in *fractional pixels* (set
to 50; this is a heuristic value) which is then converted to font
units using the current scaling value.  IMHO, this greatly improves
the appearance of hinted glyphs, reducing the number of distortions.

Please test the CVS.  I'm especially interested to improve the value
of PSH_STRONG_THRESHOLD; maybe an even smaller value is better.


    Werner