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Re: [css3-images] cross-fade()

From: Rik Cabanier <cabanier@gmail.com>
Date: Wed, 4 May 2011 14:43:34 -0700
Message-ID: <BANLkTi=nHHZQ0u43JH7-X3jZcGWCcT1rBw@mail.gmail.com>
To: "L. David Baron" <dbaron@dbaron.org>
Cc: www-style@w3.org
I *think* you're right.

It should read either:

Then, the start image has a global alpha applied to it equal to (1-p), the
end image has a global alpha applied to it equal to p, and the end image is
then composited over the start image with the plus operation

or

Then, the end image has a global alpha applied to it equal to p, and the end
image is then composited over the start image with the source-over operation

but I could be wrong...

Rik

On Wed, May 4, 2011 at 9:40 AM, L. David Baron <dbaron@dbaron.org> wrote:

> I think the current definition of cross-fade() in
> http://dev.w3.org/csswg/css3-images/#cross-fade-function is
> incorrect.  It defines cross-fade() in terms of the porter-duff over
> operator, which is not symmetric.  This means that cross-fade(A, B,
> 30%) is different from cross-fade(B, A, 70%).
>
> I *think*, though I'm not sure, that the right way to define
> cross-fade is in terms of the plus operator described in section 4.5
> of the original Porter-Duff paper:
> http://keithp.com/~keithp/porterduff/
>
> -David
>
> --
> L. David Baron                                 http://dbaron.org/
> Mozilla Corporation                       http://www.mozilla.com/
>
>
Received on Wednesday, 4 May 2011 21:44:46 GMT

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