CyanoHao
commented
4 years ago I’m trying to explain it in top-down approach.
Quad2Cubic (defined in otfcc-q2c.cpp) handles metadata of the font. It writes CFF font dict (CFF_ in JSON-serialized OpenType font file, aka “otd file”), and calls Tt2Ps to convert glyphs.
Tt2Ps (defined in tt2ps.cpp) converts TT-outlined glyphs to PS-outlined glyphs. For each in glyf in a otd file, it calls ConvertApprox to do the conversion.
In ConvertApprox, for each contour, the algorithm handles 2 quadratic segments at a time. It calls CombinePair to determine whether the 2 quadratic segments can be combined to a single cubic curve. If yes, append the combined cubic curve to cubic contour (by ConstructCffPath::Curve), or convert the first segment to cubic one (by SimpleCurve) and append it to cubic contour, the second segment to be proceeded next time.
The 2 quadratic segments that are handled at a time is stored in Point p[6].
TT points are read, proceeded, and accumulated in p. (Note that an on-curve point can be emitted if it is mid-point of 2 off-curve points.) This is implemented using a state machine as follows:
state sequence points
0=off,1=on accumulated
0 1 0
1 1 0 0-1
2 1 0 0 0-3 (p[2] is mid-point of p[1] and p[3])
3 1 0 1 0-2
4 1 0 1 0 0-3
Hi, how are you. I need some help. Firstly, I'm very happy to find this library. But, I need rewrite this library using C#. So, would you please explain the convertion arithmetic. Thanks a lot.