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

From: Robert O'Callahan <robert@ocallahan.org>
Date: Mon, 14 Jun 2010 13:34:34 +1200
Message-ID: <AANLkTimYDDyc_6Tq9hdUFC5LcqYwMIlNKCYvw-z_Ox_f@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 12:26 PM, Robert O'Callahan <robert@ocallahan.org>wrote:

> In Firefox, a blur with radius 'Npx' increases the size of the blurred
> object's (in terms of pixels affected) by exactly N CSS pixels in each
> direction ... if you ignore the effects of rounding. In practice, for large
> values of N, rounding causes pixels near the edge of the shadow to not
> change. I think this is a good way to interpret the radius and the word
> 'radius' is a reasonable term for this value.
> For the record, our blurring algorithm uses three passes of a box filter,
> similar to what's described here:
> http://www.w3.org/TR/SVG/filters.html#feGaussianBlur. We round the blur
> radius down to the nearest device pixel and then choose three (integer) box
> lobe sizes that add up to the blur radius while being roughly equal. This is
> slightly tricky. The exact algorithm is in ComputeLobes here:
> http://mxr.mozilla.org/mozilla-central/source/gfx/src/thebes/utils/gfxBlur.cpp#264

Hmm, I see that the spec has been changed so that we're supposed to blur
inside the shadow edge as well as outside. I guess that makes some kind of

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healed. We all, like sheep, have gone astray, each of us has turned to his
own way; and the LORD has laid on him the iniquity of us all." [Isaiah
Received on Monday, 14 June 2010 01:35:02 UTC

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