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Re: [css3-background] vastly different takes on "blur"

From: Brendan Kenny <bckenny@gmail.com>
Date: Mon, 14 Jun 2010 19:24:12 -0500
Message-ID: <AANLkTinHsdeUT8hHl4hA0NaEZLVU7M9ARkcIokkX_pLk@mail.gmail.com>
To: Brad Kemper <brad.kemper@gmail.com>
Cc: fantasai <fantasai.lists@inkedblade.net>, Simon Fraser <smfr@me.com>, "L. David Baron" <dbaron@dbaron.org>, Brian Manthos <brianman@microsoft.com>, "www-style@w3.org" <www-style@w3.org>
On Mon, Jun 14, 2010 at 5:55 PM, Brad Kemper <brad.kemper@gmail.com> wrote:
> On Jun 14, 2010, at 2:56 PM, Brendan Kenny <bckenny@gmail.com> wrote:
>> To me, the new text actually seems more "you know what I
>> mean"/"hand-waving" than before.
> I don't understand why spec text that describes the required results is a
> bad thing. I don't think the steps taken to get there are nearly as
> important as clearly and precisely describing how it needs to end up. It is
> a visual effect, so we need to say something about what it should look like.
>> This might not be tenable, but thinking of Simon's SVG filter
>> suggestion and looking at the spec for feGaussianBlur
>> http://www.w3.org/TR/SVG/filters.html#feGaussianBlur
>> this whole conversation might be made a lot simpler by simply
>> specifying the blur used rather than leaving it undefined.
>> If the shadow is blurred by a Gaussian blur (or its box filter
>> approximation) with a standard deviation of the blur-radius divided by
>> 3 (or the "blur width" divided by 6), the effect will be exactly what
>> we all seem to mean while still leaving room for efficient
>> implementations.
> I don't understand enough about Guassian math or whatever to say if that is
> enough or not. Is it? The Guassian blur filter in Photoshop gave me a much
> different blur width than Safari did with the same input.

That is sufficient for defining the blur, getting the effect currently
listed in the spec for "a long, straight shadow edge," and for getting
the "expected" result when blurring corners and concave shadows
(listed as concerns earlier in this thread).

I should have noted that it is subject to the rounding behavior Rob
mentioned earlier, but I believe that is as expected as well.
Received on Tuesday, 15 June 2010 00:24:45 UTC

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