[Devel] Discrepancy between freetype and Adobe Compact Font Format Spec

[Eric Nickell]

[This was previously sent to address@hidden, but I have been told
since that address@hidden is more appropriate for bug
reports/feature requests, etc.]

We have been unable to load the example CFF font contained in appendix D
of Adobe's Technical Note #5176, "The Compact Font Format Specification"
using FT_New_Memory_Face.

Freetype seems to raise an FT_Error at line 1608 of cffload.c, after
satisfying the error condition ( num_glyphs != 229 ).  (Fwiw, it seems
that the 229 might be better represented as a symbolic constant here.)

The example font contains only two glyphs, both empty. In section 13,
the spec states "A font may use a predefined charset if it exactly
matches in the first nGlyphs."  I interpreted that sentence to mean that
if the CharStrings INDEX for a font only has 2 glyphs in it, the
effective charset used is the first two charset entries of the
predefined charset.

I'm a little confused by the comment just above the FT_Error in
cffload.c, which states:

      /* In order to use a predefined charset, the following must be  */
      /* true: The charset constructed for the glyphs in the font's   */
      /* charstrings dictionary must match the predefined charset in  */
      /* the first num_glyphs, and hence must match the predefined    */
      /* charset *exactly*.                                           */

Could this be due to a difference of interpretation as to whether
"nGlyphs" refers to the number of glyphs in the predefined charset vs
the number of glyphs found in the CharStrings INDEX?

Eric Nickell