In the glyf table, if a glyph is a composite glyph, I don't understand what it means if the flag ARGS_ARE_XY_VALUES is not set. The msdn docs say
the first point number indicates the point that is to be matched to the new glyph. The second number indicates the new glyph’s “matched” point. Once a glyph is added, its point numbers begin directly after the last glyphs (endpoint of first glyph + 1).
But I have NO idea what it means:
What is a "point number"? Is it an index into the glyph's points?
Yes. It’s an index into the array of pairs of coordinates that make up the glyph’s outline (as defined in the glyph’s contour data).
What does "matched to the new glyph" mean?
It means that the new component glyph of that composite/compound glyph is to be positioned so that the coordinates of its ‘match point’ are equal to those of the ‘match point’ of the base component glyph. In other words: so that the indicated points for the two components match. This is repeated for each new component glyph, with the point numbers/indices of the already matched components being treated as if it were a single, base component glyph.