RE: [Devel] severe problems with Legendum.otf

[Turner David]

Hello,

> The problem is the different interpretation of the MSIRP instruction. 
> FreeType has an /* UNDOCUMENTED BEHAVIOUR */ part for twilight points 
> which I can't reproduce at all using Windows 95 and 2000, if I remember 
> correctly. I actually thought a patch that basically deleted that bit of 
> code was around but it wasn't applied yet because David wasn't sure this 
> wouldn't break other fonts.

I can't really tell you what's wrong with lengendum or MSIRP as implemented
in FreeType. I can however explain what the origin of the /* UNDOCUMENTED */
portions in the source code.

Simply put it, the specification I used when writing the initial bytecode
interpreter didn't produce acceptable results for the core MS Fonts like
Arial, Times New, etc...

Through heavy trial-and-error and experimentation, I could find some additionnal
code to produce correct results, and that's what the "UNDOCUMENTED" comments
are all about: code that was necessary to get adequate rendering of the core
fonts.

However, there are several undocumented portions, and there may be some
dependencies that I didn't quite spotted at the time. It's possible that
a first "UNDOCUMENTED" section later became irrelevant when a new
"improvement" was found. I didn't take the time to reduce the sections
to the minimum, however.

Now, a few simple questions:

- Does the same "incorrect" behaviour happens with FreeType 1
  (if not, something fuzzy happened when the code was ported to
  FT2)

- since you've written your own rasterizer, could you check the
  differences it has with the FreeType one(s) ? Also, does your
  code renders the MS Core Fonts perfectly ? (I suppose so, but
  who knows :-)

By the way, I'd like to point the fact that the monochrome renderer
ignores the "drop-out" mode set by the glyph program(s) because
experience has shown that this was the only way to get correct
rendering of most well-hinted fonts. Again, this assumption may
be wrong, especially if we remove or change some of the "undocumented"
sections in the interpreter.


Hope this helps,

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

--
This message and any attachments (the "message") is intended solely for the
addressees and is confidential. If you receive this message in error, please
delete it and immediately notify the sender.
Any use not in accordance with its purpose, any dissemination or disclosure,
either whole or partial, is prohibited except formal approval.
The E-Mail transmission can not guarantee the integrity of this message.
CANAL+TECHNOLOGIES will not therefore be liable for the message if modified.