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Re: Ahem font and anti-aliasing

From: Gérard Talbot <css21testsuite@gtalbot.org>
Date: Thu, 02 Feb 2017 15:33:57 -0500
To: "Myles C. Maxfield" <mmaxfield@apple.com>
Cc: Public CSS Test suite mailing list <public-css-testsuite@w3.org>, Geoffrey Sneddon <me@gsnedders.com>
Message-ID: <bc7c94a735ae632a7456f59455a0ec3d@gtalbot.org>
Le 2017-01-31 20:00, Myles C. Maxfield a écrit :
> The exact math used to compute antialiasing is a property of the
> rasterizer software. The rasterizer uses hints from various sources to
> determine which kind of antialiasing to apply. Some of these signals
> may be from the font, some may be from the user’s preferences, some
> may be from system defaults, and some may be from a higher-level
> construction like CSS. Every rasterizer pays attention to different
> signals when performing this determination.
> 
> Which environment and platforms are you interested in?
> 
> —Myles


Myles,

We had a long (scattered) thread in January 2017, here [1] and elsewhere 
[2][3], on the Firefox results when taking the Writing modes test suite. 
Geoffrey Sneddon claims that 588 tests (I do not know under which 
operating system and under which conditions exactly) fail mainly because 
of anti-aliasing differences in reftests. Under Linux and with Firefox, 
I have seen small tiny vertical lines between Ahem glyphs, at Ahem 
glyphs' edges, like in the left part of this screenshot [4].

Why can't we disable (or reduce or neutralize) anti-aliasing potential 
or effects in the Ahem font itself to begin with? Or why can't we set 
the hint (signal) from the Ahem font to disable any and all 
anti-aliasing methods?

In CSS2.1 test suite and CSS3 Writing modes test suite, we never use 
Ahem font for shapes with curvy or oblique (\/) sides; it is always for 
rectangular shapes with horizontal and vertical sides.

- - - - - -

Maybe gasp range 1 (instead of 2) would only do gridfit, if I understand 
this page:

http://www.truetype-typography.com/ttalias.htm

- - - - - -

Under Linux, I can disable system anti-aliasing and I guess (although 
not sure exactly how; haven't had time to experiment) it could do 
possible for 1 single font.

CSS properties affecting anti-aliasing:
text-rendering
-webkit-font-smoothing
-moz-osx-font-smoothing

Under Windows operating system, clearType can be turn off: 
Tools/Internet Options/Advanced tab/Multimedia section/uncheck Always 
Use ClearType for HTML

[1]:
http://lists.w3.org/Archives/Public/public-css-testsuite/2017Jan/0003.html


[2]:
Writing Mode Reftests Anti-Aliasing Failures
https://github.com/w3c/csswg-test/issues/1174

[3]:
Writing Modes PR & Testsuite
http://lists.w3.org/Archives/Public/www-style/2017Jan/0024.html

[4]:
https://bug1260387.bmoattachments.org/attachment.cgi?id=8735781

Gérard

P.S. I will be slow (slower than usual) to reply to emails for the next 
5 days or so.



> 
>> On Jan 28, 2017, at 7:18 PM, Gérard Talbot 
>> <css21testsuite@gtalbot.org> wrote:
>> 
>> Le 2017-01-28 22:02, Gérard Talbot a écrit :
>>> Myles,
>>> Would it be possible to create a version of Ahem font that would
>>> reduce or minimize or neutralize anti-aliasing? or that would specify
>>> that font smoothing (anti-aliasing) must not be applied?
>> 
>> https://github.com/litherum/AhemMaker/blob/master/AhemMaker/main.swift#L308
>> func gaspTable()
>> 
>> https://github.com/litherum/AhemMaker/blob/master/AhemMaker/main.swift#L314
>> append(result, value: UInt16(2)) // Greyscale
>> 
>> As I understand this, Greyscale is one anti-aliasing method. What does 
>> the 2 value mean here? What would be the best value to minimize or 
>> neutralize anti-aliasing in a new Ahem font version?
>> 
>> Gérard
>> --
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>> 
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>> 

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Received on Thursday, 2 February 2017 20:34:37 UTC

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