[cairo] Struggling with subpixel text (last blocker for 1.8)

David Turner david at freetype.org
Wed Oct 1 07:01:43 PDT 2008

I'm not sure I've been clear enough, because I really don't understand
whether Carl wants to do LCD filtering
in Cairo or not. Just as a clarification, the LCD-specific APIs in FreeType
have been designed in such a way
to enable the following:

1/ FreeType clients can use the LCD-specific APIs independent of FreeType's
implementation. It's still there by default
    but will return 'gray' pixmaps (where R=G=B is enforced). You can change
that with a single config macro change

2/ Whenever one wants to enable LCD filtering on their system, they only
need to update their build of FreeType.
    All other clients that use the APIs directly don't need to change their
binaries. They should just work.

So, ideally, there should be a *single* library that needs to be changed on
your system to enable the feature.

If you decide to do the filtering in Cairo / LibXft / whatever, you simply
make the situation more complex and byzantine
for everyone (distributors, packagers, end-users)

2008/9/30 Carl Worth <cworth at cworth.org>

> On Sun, 2008-09-28 at 18:17 -0500, Brandon Wright wrote:
> > David Turner wrote:
> > >If you absolutely want to support LCD filtering even if FreeType
> doesn't,
> > >then I really
> > >recommend you to simply ignore the FreeType-specific APIs and just
> > >re-implement the
> > >damn thing in Cairo.
> > >
> > >then deal with the legal consequences yourselves...
> > I agree with the point David makes here. This is subverting the most
> > logical place to cut off the filtering for legal ramifications.
> I'm sorry Brandon, but that's presuming that the original patch (for
> cairo) had "legal ramifications" as its motivation. It did not as I
> understood it, (I thought people just wanted the option of different
> kinds of filtering).
> Meanwhile, I do not think that speculation on the impact of patents is
> appropriate for the cairo mailing list. But I will say at least this
> much:
> > "Hmm, the system FreeType says sub-pixel support isn't legal here, but
> > we'll provide it anyway because that's how it's always been done."
> No. The fact that freetype was compiled with its default options in no
> way suggests that someone has made a ruling about the legality (or
> illegality) of code that wasn't compiled.
> A much more likely explanation is that the distributor (Debian, say) of
> a freetype package, (2.3.7, say), had no idea that there was new code in
> freetype, (subpixel rendering), not compiled by default. And if
> applications are using cairo or Xft for that functionality, how would
> the distributor even know that there's unused and uncompiled code
> available in the freetype source distribution.
> -Carl
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