[ft-devel] `prep' problem

[Werner LEMBERG]

Friends,


I have a font which has this buggy `prep' program:

  SVTCA[0]
  SVTCA[0]
  SVTCA[0]
  SRP0[ ]

The last command needs some data on the stack, but nothing has been
pushed (executing SVTCA three times is useless also).  Now the
problem: The current implementation runs the `prep' program on demand,
this is, as soon as the first glyph is encountered.  After this, the
`prep' program gets marked as executed if there was no error.  In this
particular case, however, there is an error (stack underflow), and the
`success' flag isn't set as a result.  The same happens while loading
the second glyph: Executing the `prep' program fails again, and so on,
and so on.  With other words: Not a single glyph of this font is
displayed if the bytecode interpreter is hinting the font.

How shall FreeType behave?  Up to version 2.3.4, the handling of
`prep' was different (it didn't cause such an error) and the glyphs
were displayed.

My feeling says that FreeType currently does the right thing: Refusing
to handle the glyphs.  Perhaps I shall add to the documentation that
in case of bytecode errors the user always has the choice to try auto
hinting?

An alternative solution is to make the interpreter stack never
underflow, this is, if the stack is empty, it simply pops zero
values.

Opinions, please.


    Werner