[whatwg] Enabling LCD Text and antialiasing in canvas

[Robert O'Callahan]

On Thu, Feb 14, 2013 at 11:59 PM, Stephen White <senorblanco at 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'.

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?

Rob
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