[Devel] updated GSUB and GPOS support in FT 1

[Werner LEMBERG]

Paul Nelson wrote in the OpenType list:

  To clarify the ordering of glyph arrays for input, backtrack and
  lookahead sequences, the following illustration is provided.  Input
  sequence match begins at i where the input sequence match begins.
  The backtrack sequence is ordered beginning at i - 1 and increases
  in offset value as one moves away from i.  The lookahead sequence
  begins after the input sequence and increases in logical order.

    Logical order -      a  b  c  d  e  f  g  h  i  j
                                     i
    Input offsets -                  0  1
    Backtrack offsets -  3  2  1  0
    Lookahead offsets -                    0  1  2  3

A similar statement will be in the OpenType 1.4 specification.  I've
updated FreeType 1's GSUB and GPOS code to support this behaviour.


    Werner