[cairo-bugs] [Bug 10301] LCD filtering patch

[bugzilla-daemon at freedesktop.org]

http://bugs.freedesktop.org/show_bug.cgi?id=10301





--- Comment #67 from Carl Worth <cworth at cworth.org>  2008-10-11 09:25:38 PST ---
(In reply to comment #66)
> Hello again. I was curious, so I added a new section to my comparison page
> juxtaposing Vista and Cairo:
> http://www.alice-dsl.net/towolf/cairo/#vista

Hello again,

While you're adding new images, I'd like to write up a couple quick thoughts
based on your presentation so far.

First, you seem to be largely arguing for a change in the default filtering,
beyond just adding code to allow for the freetype filtering to be used. That's
certainly a useful discussion to have. But oddly, the images on the page don't
actually show direct comparisons of the different choices we have here for a
default. I'd like to see the results of cairo's current code compared to
freetype's LEGACY and that compared to FIR3 and FIR3 compared to FIR5. Things
like that.

You also limit the presentation by saying "This is not a test of the boring
canonical high contrast scenario with bytecode hinted DejaVu Sans, 8pt text,
and pixel-fitted stems.". As "boring" as that scenario might be, it's a
terribly important one, so I would really like to see some examples of that
added if you would. I'd like to ensure a "do no harm" situation here.

Meanwhile, another problem I had with the original patch series was that it
simply exported all of the freetype filters as-is up to the user level through
cairo's public API. One problem with this is that the filters are all obviously
freetype-specific while cairo provides a cross-platform API. An argument for
providing the API is for someone like Behdad to be able to write a
font-preferences dialog that presents (unnamed) font-rendering samples to the
user and lets them simply click on which one they prefer.

But for that kind of font-preferences dialog, we already have 3 different
ANTIALIAS font options and 4 different HINT_STYLE options. So that's 12
different necessary samples now, and adding 4 different filters expands that to
48, which seems to go way beyond what any user could ever want to see.

Meanwhile, the descriptions on your page seem to argue for specific filters
being best in specific situations. For example, there seems to be an implicit
preference for FIR5, (no FIR3 examples, and a link to an Ubuntu poll favoring
FIR5). So is there any reason to provide FIR3 at all? Also, you argue that
LEGACY doesn't do well in anything but the strongly-hinted case, but does it
(or cairo's code?) actually do best there?

I'm wondering if we shouldn't automatically choose a filter based on the
HINT_STYLE option. I'm also wondering that if we do decide to expose these in
the API whether we should just export two options absed on their general
characteristics, (INTER_PIXEL and INTRA_PIXEL ?), rather than so much about
their details implementation, (FIR3 and FIR5, etc.).

Well, this is all a little bit off-topic for the specific bug here, and it's
getting into API discussion that really needs to take place on the cairo list.

Let's move the discussion there. Feel free to quote my stuff liberally or
completely if you'd like to reply on the list.

Thanks,

-Carl


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