[whatwg] Enabling LCD Text and antialiasing in canvas

Rik Cabanier cabanier at gmail.com
Thu Feb 21 16:01:49 PST 2013

On Fri, Feb 22, 2013 at 10:33 AM, Robert O'Callahan <robert at ocallahan.org>wrote:

> I think Rik is convincing me that we shouldn't expose mozOpaque or any
> other explicit subpixel AA control to the Web. It will be very easy for Web
> authors to test it in one place and discover that it works without
> realizing that they're causing problems for some users.
> I think a fully automatic solution that tries to use subpixel AA but is
> always able to render grayscale AA if needed is the way to go. Possibly
> with an author hint to suggest opting into a more expensive rendering path.
Great! I think matteColor (or matteStyle to be more consistent) can easily
be implemented. We can optimize rendering later.

So, if a mattecolor is set the UA can assume that:
- all compositing operation within the canvas can ignore background alpha
- the canvas can be copied directly to the screen (unless another effect is
applied to the canvas element or its ancestor)

If mattecolor is set, the UA should matte with that color. If a compositing
operation (that introduces alpha) is used, the matte operation needs to be


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