[Devel] Curves that make you hmmmmm....

[Tom Kacvinsky]

I just saw a proposed change go by one the ghostscript lists that started as
(in effect):

in a TT font, there may be curves that *start* on an off-curve point...

The operative word being start, and the crucial point (no pun intended) being
that this point is off curve.  This cannot happen with a Type 1 font just 
because
of how the Type 1 operators work.  But it may be possible in a TT font.   So, 
how
does FT handle this in the TT curve constructor?  I admit I haven't looked
yet...

Also, while I am at it, I ran across a True Type CID font in a PDF file (from
some ghostscript testing I was doing) that when printed from Acrobat had glyphs
whose path intersections were "painted" white.  This, I think, is a bug in
whatever Type 42 rasterizer exists in the printer.  But this raises a question:
how does FT handle TT glyphs which are drawn as a set of overlapping paths?  For
a Type 1 font, one would find the paths that trace the overall shape of the
overlapping paths (such that the final paths have no overlap) and use those new
paths in the actual font, but for a TT font, this has to happen on the fly.
Actually, it may have to happen on the fly for Type 1 fonts.  If I recall
correctly, the T1 spec doesn't explicitly state that it is technically incorrect
for two paths to overlap, though it does recommended that this not happen.

Anyway, I suspect that the path overlap problem is not taken care of during
curve construction time (at least this is true for CFF and Type 1 fonts).
Rather, the overlap problem is taken care of at rasterization time.  Just fill
paths 1 through n, using some curve filling method that fills the intersection 
of
two overlapping paths with black.

Am I on the right track?