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Re: Text anti-aliasing on the Mac

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Wed, 3 Oct 2012 13:25:01 -0700
Message-ID: <CAAWBYDD=5H_LUc0iRwiFVfQLfE2JrW31t=+SqXPTa_tcFDqiuw@mail.gmail.com>
To: John Daggett <jdaggett@mozilla.com>
Cc: www-style list <www-style@w3.org>
On Wed, Oct 3, 2012 at 10:57 AM, Tab Atkins Jr. <jackalmage@gmail.com> wrote:
> On Tue, Oct 2, 2012 at 8:23 PM, John Daggett <jdaggett@mozilla.com> wrote:
>> 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.

According to the implementor that did the Chrome 22 change, you're
wrong, John.  The glyph dilation occurs as a result of OXS's
auto-hinting.  Here's his exact words:

> This is not true. The OSX rasterization is not actually any
> heavier, they actually do auto-hint the outlines to dilate them.
> This is auto-hinting. You can't obtain the auto-hinted outlines,
> but those dilated outlines are what is being rasterized. Saying
> otherwise is completely disingenuous. Basically, when you ask
> for lcd smoothed text from CoreGraphics, you get fake bold.

~TJ
Received on Wednesday, 3 October 2012 20:25:48 GMT

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