Re: [Devel] Help me understand this... I'm loosing my sanity. Please.

[Vincent Caron]

> 1. TTF files have both a data part and a code part. The code part is
> made of bytecode, which describes how to deform the font in order to
> render them better with low-resolutions. The byte-code interpreter can
> be used with both antialiased and unantialiased fonts.

True.


> 2. For patents problems, freetype2 introduces an auto-hinting module,
> which IGNORES the bytecode BUT tries to achieve a decent hinting
> effect nevertheless. This auto-hinting module can also be used BOTH in
> antialiased and unantialiased fonts.

True.


> 3. The freetype2 implementation can EITHER use the bytecode
> interpreter OR the auto-hinting, but not both at the same time. And
> the choice is made at compile time, with
>
>        #define TT_CONFIG_OPTION_BYTECODE_INTERPRETER

If you compile the TrueType byte code interpreter, you still have the 
choice between 'native hinging' (byte code) and 'auto hinting' at runtime.


> 4.  maybe redhat 8-9 activates the bytecode interpreter, whereas
> debian doesn't?  That would explain the better rendering of fonts in
> redhat.

RedHat 9 does not compile in the byte code interpreter due to the patent 
issue. Quoting Matt Wilson, RedHat : "We would prefer to enable the 
patented TrueType hinting algorithms in FreeType to improve our font 
rendering, but this is not possible."

  http://osnews.com/story.php?news_id=3219


> 5. maybe debian uses auto-hinting in replace. That would explain why
> the fonts are not as awful as in the nopatents.png picture.

The TrueType Debian maintainer (Anthony Fok) chose to compile the byte 
code interpreter a while ago. Today, I can testify that in my 
Debian/unstable the macro is defined in the libfreetype6-dev package.

Now the question is : does the GTK and/or Qt font frontends (thus Xft2 
?) invoke native or autohinting ? My guess is 'native' if present, auto 
otherwise. There is a per-distro configuration issue I guess.


> 6. how can I know if the debian libfreetype6 package I am using
> activates the byte-code interpreter? I DID read
> /usr/share/docs/libfreetype6/README.Debian but there is no mention.

$ grep -r BYTECODE /usr/include/freetype2
/usr/include/freetype2/freetype/config/ftoption.h:  /* Define 
TT_CONFIG_OPTION_BYTECODE_INTERPRETER if you want to compile   */
/usr/include/freetype2/freetype/config/ftoption.h:#define 
TT_CONFIG_OPTION_BYTECODE_INTERPRETER

The defined would be commented out if the interpreter was not compiled in.


> 7. I noticed that redhat 8 sets the following resources by default:
>
> Xft.dpi:        96
> Xft.hinting:    true
> Xft.hintstyle:  hintmedium
>
> What do they mean? What reads them? Where can I find more info about
> them?

Xfd.dpi forces an arbitrary resolution for the output device (your 
screen). This is the unit that links 'points' and 'pixels'. Due to 
habits in the Windows and Mac world, it is preferable to use common 
values rather than the 'real' value (plug'n'play monitor can tell their 
physical resolution to your computer).

For other fields, I guess you'll need to have a look at the Xft2 
documentation. I think that all you need to know about the great new 
unified (client-side, anti-aliased, <insert buzzword>) font rendering 
for X is here : http://fontconfig.org/


> 8.  I can't see why in redhat 9, openoffice.org's menus are
> antialiased, and in debian this is not the case. I don't know if the
> problems are related, so I just thought to mention it.

Could you check which library OpenOffice is using ? Run 'ldd' on the 
binary, Xft2 clients have a libXft.so.2 dependency for instance. You can 
compare with other binaries of course.

Regards,

        Vincent.