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Re: [css3-background] Where we are with Blur value discussion

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Tue, 20 Jul 2010 17:47:36 -0700
Message-ID: <AANLkTineEC1dvah73AAR0BQh2ou0bPeuJBxCwjSmKl-q@mail.gmail.com>
To: Aryeh Gregor <Simetrical+w3c@gmail.com>
Cc: Brad Kemper <brad.kemper@gmail.com>, "L. David Baron" <dbaron@dbaron.org>, Simon Fraser <smfr@me.com>, Brendan Kenny <bckenny@gmail.com>, www-style list <www-style@w3.org>
On Mon, Jul 19, 2010 at 3:53 PM, Aryeh Gregor <Simetrical+w3c@gmail.com> wrote:
> Then it will look different between different browsers.  We should try
> to not write specs that allow this unless there's a specific good
> reason, like respecting platform conventions or limiting optimization
> opportunities.  If browsers use entirely different blur algorithms,
> then they will diverge a lot in edge cases at the very least, and
> that's not interoperable.  Mandating that browsers should use one
> particular *pixel-specific* blur algorithm (or close approximations
> thereto) is the correct thing to do, if implementers are okay with it
> -- which isn't clear to me at this point.

I'm digging in deeper with our Skia devs to see what the precise
reasoning was behind using what appears to be a single box-blur.  As I
said before, I think it was for performance reasons, but I'm trying to
get an answer from the horse's mouth before I come down hard on one
side of the issue or another.

If it turns out that the performance savings of Skia blurs really
aren't that important, and that it would be fine to just change our
impl to do a triple box-blur like I think everyone else does, then we
can define the conformance criteria as each pixel having to be within
X% of a gaussian blur with stdev equal to half the blur length.  (X%
being probably 3% or 5%.)  That'd pass everyone who's doing pretty
blurs right now, and pass Chrome on all platforms once we change Skia
to be prettier.

Received on Wednesday, 21 July 2010 00:48:28 UTC

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