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Re: A property for font antialiasing control on Mac OS X

From: Dirk Schulze <dschulze@adobe.com>
Date: Thu, 18 Jul 2013 07:31:59 -0700
To: Rik Cabanier <cabanier@gmail.com>
CC: "L. David Baron" <dbaron@dbaron.org>, "www-style@w3.org" <www-style@w3.org>
Message-ID: <AED13979-6DDE-4EC6-81D5-BA6E5ED7584F@adobe.com>

On Jul 17, 2013, at 7:39 PM, Rik Cabanier <cabanier@gmail.com> wrote:

> On Wed, Jul 17, 2013 at 5:58 PM, L. David Baron <dbaron@dbaron.org> wrote:
> On Wednesday 2013-07-17 17:04 -0700, Rik Cabanier wrote:
> > Other cases where you might want to turn off anti-aliasing:
> > - animations
> > when animating text, you don't want to anti-alias because of performance
> > and also because subpixel AA will cause "jiggling" of characters when you
> > move a text run
> The jiggling is a result of subpixel *positioning* of text (which
> also requires re-rasterizing for the different subpixel positions,
> which integer shifts don't).  I think that's independent of
> antialiasing.
> It depends how you do subpixel AA. I agree that in most cases you won't be able to tell the difference.'

The property I was speaking about is 'text-rendering'. If you use text-rendering: geometricPrecision you won't see the described problems.

> > - content that will end up in a 3d transform
> Implementations already know how to disable subpixel AA here;
> authors don't need to give hints.
> I think you misunderstood.
> What I meant is that if you have text that is going to be animated, transitioned or will have a 3d transform applied to it, you want to disable subpixel positioning. Otherwise you will notice a change in rendering when it is animated.

Try the text-rendering property on SVG content. Would be interesting if you still experience issues during text animations (with SVG animations on <text>). I did not test if this property works on HTML content as well, but assume that this depend on the platform. After all, it was just specified for SVG in the first place. On SVG I did not experience AA issues with this property set.


> Other cases where an author might want this, is if the element that contains the text:
> - becomes transparent
> - has a filter applied to it
> - has blending applied to it 
> > - match canvas text
> > Text in canvas never uses subpixel-AA (although there are some browsers
> > that allow it) and an author might want to match HTML text with Canvas text
> I don't think this is a strong use case.
> Unsure. How about text in an SVG image?
> > Maybe for background-clip you might want the text to be a hard clip and not
> > antialiased?
> I don't think antialiasing of text will ever cause it to extend
> outside a clip that it's in.
> Doesn't background-clip use the text as a clipping path for the background image? If so, you might not want blurry edges
> > Because of transition, animations and 3d transform, I don't believe that
> > this will be a temporary solution (unless of course display technology
> > advances so much that subpixel-AA is no longer needed)
> I think in the long run, as display densities increase, we may well
> be moving towards subpixel AA no longer being needed.  But that's
> probably a long ways off.  I don't think your other examples are use
> cases for author control (nor have I heard of such author control
> ever being provided on platforms other than Mac).
> -David
> --
> 𝄞   L. David Baron                         http://dbaron.org/   𝄂
> 𝄢   Mozilla                           http://www.mozilla.org/   𝄂

Received on Thursday, 18 July 2013 14:32:30 UTC

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