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

From: Brad Kemper <brad.kemper@gmail.com>
Date: Fri, 16 Jul 2010 16:29:03 -0700
Message-Id: <B90C2EE8-A06D-455E-9659-98DDF0E0562A@gmail.com>
Cc: "Tab Atkins Jr." <jackalmage@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>
To: Aryeh Gregor <Simetrical+w3c@gmail.com>
On Jul 16, 2010, at 3:20 PM, Aryeh Gregor <Simetrical+w3c@gmail.com> wrote:

> On Thu, Jul 15, 2010 at 8:45 PM, Brad Kemper <brad.kemper@gmail.com> wrote:
>> I mean that you seem to be arguing against the sort of language we have in the draft, because you want the blurs to be pixel perfect. Yet the part you are objecting to is the part that attempts to have measurable results that match the author's input length, and replace it with something where the only way to measure the result is to compare it to results in other standards (which are similarly vague in their wording).
> I still don't get what you're saying.  Both canvas and SVG are
> absolutely precise: a given input maps to a Gaussian blur with sigma
> equal to a specific well-defined value. 

That's fine if you're an implementor, I suppose, but it's fairly meaningless to the authors who will be using it every day. I want to be able to say, "give me a blur that extends out 40px", and then verify that it has done so. This is a testable result that anyone who can count the pixels can verify. If the only way to verify is by using a complex formula that ordinary authors don't understand (Tab's math-jitsu is extraordinary) or by comparing it to other implementations of other specs,  then that's not good enough. If, on the other hand, I can say, "give me a blur that extends out 40px" by typing '40px' into the appropriate part of the rule, then that is not only intuitive, it is something that the UA can create very precisely with a Gaussian blur or any other kind of blur. 

>> As far as how smooth the blend is, or how the shades are distributed within that space, I think that's less important, as long as the blend perceptibly fills the space it is supposed to, and is not so heavily weight to one end or the other that it noticeably changes the whole character of the blur. If an implementor wants to improve performance by, say, having 2 identical opacity pixels adjacent to each other in a large blur, rather than having a tenth of a percent of difference between them, I think that would probably be fine, as long as the blur width (or blur extending amount) matched what the author asked for.
> That's not so easy to automatically test,

I've seen some pretty clever tests. I expect to see more. 

> and results will vary more.

The spec allows some variance, so that the UA can make decisions that balance beauty, performance, memory footprint, etc. But the width of the blurry part of the shadow should be precise and easily and intuitively understood by authors. 

> I don't see the problem with setting a reference in terms of Gaussian
> blur, 

I also don't see the problem with having a reference example of a Gaussian function that fulfills the clearly-worded pixel width requirements of the spec. 
Received on Friday, 16 July 2010 23:30:32 UTC

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