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

From: Rik Cabanier <cabanier@gmail.com>
Date: Fri, 15 Feb 2013 14:44:13 +1100
Message-ID: <CAGN7qDCQyb-_ioWRWoxBiQwAL7N2K5rPukbjWt7g-XjFfC509A@mail.gmail.com>
To: robert@ocallahan.org
Cc: whatwg@whatwg.org, Ian Hickson <ian@hixie.ch>, Stephen White <senorblanco@chromium.org>
On Fri, Feb 15, 2013 at 2:21 PM, Robert O'Callahan <robert@ocallahan.org>wrote:

> On Thu, Feb 14, 2013 at 11:59 PM, Stephen White <senorblanco@chromium.org>wrote:
>
>> I think this is difficult to do in the general case, such as
>> putImageData() or drawImage() or patterns, since you would need to examine
>> all the pixels of the source image to determine if they contain non-1
>> alpha.  This would be cost-prohibitive.
>
>
>> If it's just for the purposes of optimization, you could be conservative
>> and simply clear the flag when there's the potential for (but not certainty
>> of) non-1 alpha.  But if you're also using that flag to allow subpixel AA,
>> the behaviour becomes quite unpredictable for the web developer and hard to
>> spec crisply.
>>
>
> What if we just said
> a) non-over operators clear the subpixel AA flag
> b) putImageData clears the subpixel AA flag
> Both of these are infrequently used AFAIK. Authors could work around most
> cases of b) by doing putImageData to another canvas and compositing it into
> the destination with 'over'.
>

Yes, that's pretty much my proposal. Except putImageData could detect it
but that might be too hard for authors to figure out.


>
> How bad would that be? Would it help if we added an attribute to the
> canvas to let authors detect whether the subpixel AA flag is set?


I think that would be very helpful.

So, if you clear (or matte) the canvas, the flag becomes true but if you do
an operator that removes alpha, it will become false.


>
>
> Rob
> --
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>
Received on Friday, 15 February 2013 03:44:39 UTC

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