Mailinglist Archive: opensuse-bugs (8956 mails)

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[Bug 213989] cairo needs a LCD filtering patch
  • From: bugzilla_noreply@xxxxxxxxxx
  • Date: Fri, 20 Oct 2006 10:09:35 -0600 (MDT)
  • Message-id: <20061020160935.DB13DF1F@xxxxxxxxxxxxxxxxxxxxxx>
https://bugzilla.novell.com/show_bug.cgi?id=213989





------- Comment #1 from mfabian@xxxxxxxxxx 2006-10-20 10:09 MST -------
First some background information:

freetype versions <= 2.2.1 always could do sub-pixel-hinting
(the "coloured" rendering).

David Turner seems to believe now that Microsoft has
Patents for practically *everything* which has to do with
sub-pixel-hinting:

David Turner> I have been relunctant to publicly comment on this issue, but I
think
David Turner> it's the right time now, because while the news aren't so good,
in my
David Turner> opinion, the more people are aware of it, the better. I've also
CC-ed
David Turner> Keith Packard and Carl Worth to this message since this will have
an
David Turner> impact on the code they distribute.
David Turner>
David Turner> first of all, the reason why the patches were taken down is
simply
David Turner> because my ISP lost all the files on my "personal web space"
hosted on
David Turner> their servers. it seems I can't upload anything there anymore,
and it
David Turner> has all to do with incompetence, not malice.
David Turner>
David Turner> However, I've been reluctant to propagate the files through other
David Turner> means, because I wanted to analyze the Microsoft patents. That's
David Turner> mainly because I intended to move the LCD-filtering capability
into
David Turner> FreeType itself, and didn't want to be responsible for yet
another
David Turner> sub-marine patents that could make millions for MS in a few
years,
David Turner> once the technique is being used in all kinds of gizmos like
mobile
David Turner> phones and PDAs; incorporated by unsuspecting developers.
David Turner>
David Turner> And my final understanding is that the MS patents pretty cover
*all*
David Turner> cases of LCD-specific rendering we're interested in (there are
David Turner> ClearType patents that clearly don't affect us). And by the way,
this
David Turner> includes the original LCD-specific code found in libXft, Cairo,
and
David Turner> probably the XRender implementation of your X11 Server, even
without
David Turner> my FIR-filter patch.

David's complete mail here:

http://lists.gnu.org/archive/html/freetype/2006-09/msg00064.html

Almost everything we released up to CODE10 contains code for
sub-pixel-hinting in freetype2, libXft, XRender, Cairo and could be
affected by problems with patents concerning sub-pixel-hinting.

Now David has introduced a new compile time option
FT_CONFIG_OPTION_SUBPIXEL_RENDERING in freetype2. One has to
explicitly define that option if one wants freetype2 to support
sub-pixel-hinting.

The upstream default does not define that option.

The freetype2 version we currently have in STABLE
(freetype2-2.2.1.20061013) already is like that. Currently the option
is *not* defined in STABLE, i.e. we currently loose the capability for
sub-pixel-hinting.

Actually it is even worse that that: In order to make
sub-pixel-hinting a compile time option *and* to move the LCD
Filtering code from libXft and Cairo into freetype2, the current
version of freetype2 does not work well with the current libXft and
Cairo.

libXft and Cairo still do some colour filtering on the rendered glyphs
they get from freetype2. This leads to hideous results with freetype2,
no matter whether the subpixel hinting option is compiled into
freetype2 or not.

If freetype2 has been compiled *without* sub-pixel-hinting, libXft
nevertheless does some colour filtering if sub-pixel-hinting is
enabled for example in KDE. This just leads very ugly glyphs
which look extremely coloured for no good reason.

Even if freetype2 has been compiled *with* sub-pixel-hinting, the
fonts on our desktop still look strange. That is because some of the
LCD filtering is done in freetype2 in that case and that doesn't work
well with the extra filtering done in libXft and Cairo.

David's complete mail here:

http://lists.gnu.org/archive/html/freetype/2006-09/msg00069.html


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