Re: [ft-devel] compressed psnames table

[David Turner]

Werner LEMBERG a écrit :
> David,
>
>
> please add an explanation to glnames.py how the compression scheme for
> the psnames table work.
OK, I've commited it.

- David Turner
- The FreeType Project (www.freetype.org)

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# here's an explanation about the way we now store the Adobe Glyph List.
# First of all, we store the list as a tree. Consider for example that
# you want to store the following name mapping:
#
#  A         => 1
#  Aacute    => 6
#  Abalon    => 2
#  Abstract  => 4
#
# it's possible to store them in a tree, as in:
#
#  A => 1
#  |
#  +-acute => 6
#  |
#  +-b
#    |
#    +-alone => 2
#    |
#    +-stract => 4
#
# we see that each node in the tree has:
#
# - one or more 'letters'
# - an optional value
# - zero or more child nodes
#
# you can build such a tree with:
#
#   root = StringNode( "",0 )
#   for word in map.values():
#     root.add(word,map[word])
#
# this will create a large tree where each node has only one letter
# then call:
#
#   root = root.optimize()
#
# which will optimize the tree by mergin the letters of successive
# nodes whenever possible
#
# now, each node of the tree is stored as follows in the table:
#
#   - first the node's letters, according to the following scheme:
#
#
#         name         bitsize     description
#         -----------------------------------------
#         notlast            1     set to 1 if this is not the last letter
#                                  in the word
#         ascii              7     the letter's ASCII value
#
#   - then, the children count and optional value:
#
#         name         bitsize     description
#         -----------------------------------------
#         hasvalue           1     set to 1 if a 16-bit Unicode value 
follows
#         num_children       7     number of childrens. can be 0 only if
#                                  'hasvalue' is set to 1
#         if (hasvalue)
#           value           16     optional Unicode value
#
#   - followed by the list of 16-bit absolute offsets to the children.
#     Children must be sorted in increasing order of their first letter.
#
# All 16-bit quantities are stored in big-endian. If you don't know why,
# you've never debugged this kind of code ;-)
#
# Finally, the root node has first letter = 0, and no value.