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Re: [whatwg] Enabling LCD Text and antialiasing in canvas

From: Gregg Tavares <gman@google.com>
Date: Wed, 13 Mar 2013 19:28:25 -0700
Message-ID: <CAKZ+BNpdg5haPi+w=ki8jCnidXYwdKZpJCvtsTnV2JeuR67S3A@mail.gmail.com>
To: "Robert O'Callahan" <robert@ocallahan.org>
Cc: Stephen White <senorblanco@chromium.org>, WHAT Working Group <whatwg@whatwg.org>, Ian Hickson <ian@hixie.ch>, Rik Cabanier <cabanier@gmail.com>
On Wed, Mar 13, 2013 at 1:18 PM, Robert O'Callahan <robert@ocallahan.org>wrote:

> On Thu, Mar 14, 2013 at 8:04 AM, Gregg Tavares <gman@google.com> wrote:
>
>> It seems like an opaque canvas should be an orthogonal issue to
>> subpixel-aa. Subpixel AA seems like it should be a Canvas2DRenderingContext
>> setting though maybe with a name like
>>
>>    ctx.antialiasingRenderQuality =
>>
>> With options of
>>
>>    none
>>    grayscale
>>    bestForDeviceIfAxisAlignedAndNotScaledOrBlended
>>
>
My mistake. They should be

    none
    alpha

bestForDeviceIfNotCanvasIsNotRotatedAndCanvasIsNotScaledAndCanvasIsOpaque

;-)

Yes, I know that's a horrible name but it spells out the limitation of the
higher quality aa needed on some devices. A dev can opt in (Since the
default is alpha which is what happens today).

If they opt in

(a) it will look good if they follow the rules

and

(b) as the world transitions to HD-DPI it will end up being alpha so it's
forward compatible.




> Ugh!
>
>
>> This would let the developer choose. It would be clear what the limits
>> are, when to use it, and would let the developer choose what they need,
>> even in an opaque canvas.
>>
>
> Then we would need to come up with a spec for what happens when you
> composite subpixel AA over non-opaque pixels, including how the per-channel
> alpha values are combined to form a single alpha value. IIRC in some cases
> (D2D) you just can't do it.
>
> If we said that in a non-opaque canvas, subpixel AA is treated as
> grayscale, that would be OK.


sure.


>
>
> Rob
> --
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> lbh zhfg or lbhe freinag, naq jubrire jnagf gb or svefg zhfg or lbhe fynir
> — whfg nf gur Fba bs Zna qvq abg pbzr gb or freirq, ohg gb freir, naq gb
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>
Received on Thursday, 14 March 2013 02:28:51 GMT

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