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Re: [css3-multicol] Test with excessively wide column-gaps

From: Dirk Pranke <dpranke@chromium.org>
Date: Wed, 7 Aug 2013 15:33:48 -0700
Message-ID: <CAEoffTDHcX4UVStSmzdMrV5=A3YjYgdjKBLtjO=3_-mFQzpQbg@mail.gmail.com>
To: Morten Stenshorne <mstensho@opera.com>
Cc: www-style@gtalbot.org, HÃ¥kon Wium Lie <howcome@opera.com>, www-style mailing list <www-style@w3.org>
On Wed, Aug 7, 2013 at 3:07 PM, Morten Stenshorne <mstensho@opera.com>wrote:

> "Gérard Talbot" <www-style@gtalbot.org> writes:
>
> > We have hundreds of tests which use Ahem font and correspondent reference
> > test files using images. This is the first I hear about what you say. So,
> > this is somehow worrisome.
>
> OK, maybe my setup is weird. :)
>
> Can't say I'm too fond of the Ahem font. I try to avoid it when writing
> tests. I guess I've seen too many Ahem tests with expectations that not
> all font engines can live up to (like now). In my pessimistic mind, an
> Ahem rendering can only be compared with another Ahem rendering, and not
> with images, filled squares, etc. I usually end up using (inline-)blocks
> with a background instead, or if I really have to use text, I just use
> the default font, since I don't expect to be able to assume anything
> about how Ahem text is going to be rendered (or even laid out), anyway.
>
> BTW, on the computer I use now (Ubuntu something), Presto displays an
> ugly half pixel wide vertical stripe between the characters in your
> test. There are so many ways to "fail". :)
>
> > Do you have ClearType on or off? Do you use ClearType default, initial
> > setting?
>
> I don't think I've changed anything. I don't have access to that
> computer right now, so I can't tell you more. I was running Windows 7
> with IE10 inside a VirtualBox that runs under Debian. That might be a
> clue, I suppose.
>
> > Are you using a color LCD display?
>
> Yes.
>
> > Is the phenomenon still occuring in all/every ClearType Text Tuner
> > situations?
>
> I could check.
>
> > If you reset all IE10 settings to factory default, is there still a half
> > pixel offset affecting test versus reftest ?
>
> I could try that as well.
>
>
As another data point, in Blink (Chromium), we see a large number of test
failures on Mac OS 10.8 when rendering tests containing the Ahem font with
text antialiasing enabled; when I turned off antialiasing, the failures
went away.

It's possible this is some weirdness in the font definitions for Ahem that
could be corrected. It's also possible that this is a bug in Core Graphics
or our graphics libraries. However, we also turn off antialiasing by
default on our other platforms when running tests (and I believe Apple also
turns off antialiasing by default in WebKit).

I think it is fairly safe to say that antialiasing text can cause reference
tests to fail in ways that you wouldn't expect by simply looking at the
tests and assuming that everything just has integer precision and
quantization.

-- Dirk
Received on Wednesday, 7 August 2013 22:34:35 UTC

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