Hey Carl,
thanks to you! We come closer to the point---great! ;-)
I really enjoyed your detailed explanation. I did know before that hinting
makes use of the knowledge where pixels are (to make antialiasing become less
fuzzy) and subpixel hinting makes use of the fact that a pixel isn't a pixel
but three of them (red, green, blue)---but nothing more. Although I had some
signal processing courses at university and although I understand more about
it after your description, I am still far from beeing a font rendering pro
;-). For example, I still do not get how the subpixel and hinting renderer
knows, where the (sub-)pixels are. But this is no course in font rendering :)
So please excuse, I didn't follow your links in detail. It is not a lack of
interest but a lack of knowledge.
But I hope I got the important points:
> Then when you enable sub-pixel rendering, both applications start using
> various colors on the edges of the glyphs. So it's not the case that
> anything is simply ignoring your configuration.
Now you mentioned it, I can see it.
The thing that still confuses me is that both Konqueror and Iceweasel have
colored edges in their window title font in
withoutsubpixelhinting(hintmedium,nativ).png
Okay. So there is a patch, which changes cairo to use the subpixel filtering
of freetype instead of its own and it is this one proposed here
http://bugs.freedesktop.org/show_bug.cgi?id=10301
right? And my Debian version does not use it. Is this the patch applied to the
Debian package by the Ubuntu guys (resulting in the font rendering I
personally prefer)?
http://archive.ubuntu.com/ubuntu/pool/main/c/cairo/cairo_1.8.8-2ubuntu1.diff.gz
http://packages.ubuntu.com/en/source/karmic/cairo
Is it that what distinguishes the packages "cairo-lcd" and "cairo" in arch
linux?
http://wiki.archlinux.org/index.php/Fonts#The_original_.22LCD.22_packages
> Cairo does not currently use freetype to do the filtering.
> I'm guessing that konqueror does, (but that's only a guess---
> Qt could be doing its own filtering as well).
Yeah, I think that is what Qt=>4.5 does---at least if I parse
http://labs.trolltech.com/blogs/2008/09/01/subpixel-antialiasing-on-x11/
correctly.
To summarize: The behavior I reported is not directly a bug, but we have a
typical feature vs. bug issue here, because it is a matter of taste which
subpixel filter looks better:
> I happen to be in the camp that really does prefer vertical stems
> to be rendered as sharp as possible, (without blurring into
> neighboring columns of pixels).
Therefore I suggest: Would it be a possibilty to let users decide (either by a
config option or by providing two different packages, as the arch linux people
do---if it's that what they're doing)? Ok, as you say, it results in more
(complicated) options:
> I've personally been unwilling to add an option to cairo to control
> sub-pixel filter until someone can propose names for the options
> that actually map to differences the end user would like to effect.
I completly understand that. Somehow, these Qt guys must have solved this
problem as well---at least the selection of the subpixel filtering algorithm‽
Maybe it would be good to do it the same way‽
> Yes, this is "hinting style". And for this, I can see code very clearly
> in cairo that reads these values from fontconfig and sets corresonding
> options within freetype. See here for example:
>
> http://cgit.freedesktop.org/cairo/tree/src/cairo-ft-font.c?id=26e9f149063b9
> e1fdb54fc54fccbefdf04a68190#n1387
>
> So I would be very surprised if this wasn't working.
Yepp. It works perfectly AFAICS.
Thanks again and kind reagrds,
micu
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