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Re: Text anti-aliasing on the Mac

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Wed, 3 Oct 2012 10:57:39 -0700
Message-ID: <CAAWBYDAqGPU1sPbWN6Jmpy9eNNKkXAOrng+GQNyi-F7fn-oTdQ@mail.gmail.com>
To: John Daggett <jdaggett@mozilla.com>
Cc: www-style list <www-style@w3.org>
On Tue, Oct 2, 2012 at 8:23 PM, John Daggett <jdaggett@mozilla.com> wrote:
> Tab Atkins wrote:
>> More investigation into this issue has shown that the problem is
>> different than what I explained at the start of the page.  It's not
>> *really* about the AA.  However, a proprietary property we have
>> (-webkit-font-smoothing) which lets you switch between AA modes
>> *also* has the effect of turning hinting on or off.  Chrome 22
>> changed that, so that it no longer had this side effect.
>
> Tab, can you provide some simple examples with screenshots to
> illustrate what you're talking about here?  I think you're mixing up
> hinting/rasterization/shaping but I can't quite tell from the language
> you're using.

I pointed to a Chromium bug with before/after shots earlier in this
thread: http://code.google.com/p/chromium/issues/detail?id=152304

> The -webkit-font-smoothing property is basically a way of directly
> accessing controls that are CoreGraphics specific (i.e. OSX specific).
> What do they do for Chrome on Windows, where the underlying
> rasterizer used (GDI) isn't the same?  There are rough equivalents but the
> results are *not* the same.
>
> What do you mean by hinting here?  I think you're confusing the
> rasterization of the outlines and their adjustment via hinting
> instructions.  In general, the OSX rasterization is heavier than the
> GDI rasterization of the same outline. Hinting instructions are
> generally ignored on OSX but are used in GDI and DirectWrite.

I really don't know. :/  All I know is that we have ways to render
fonts both "skinny" and "fat" on Mac, and that we've traditionally
made this user-switchable via the -webkit-font-smoothing property,
which is *nominally* about anti-aliasing behavior, but appears to do
more than that.

We had a meeting with the guys that submitted the Chrome 22 change,
but it apparently didn't go into enough detail.  Either we asked
confusing questions, or they considered it obvious enough to not
explain, but regardless, I'm *confused*.  I'll try and set up another
meeting so we can dig into this properly.

~TJ
Received on Wednesday, 3 October 2012 17:58:26 GMT

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