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

From: Brad Kemper <brad.kemper@gmail.com>
Date: Mon, 21 Jun 2010 18:49:22 -0700
Message-Id: <19C10DC3-6D23-4586-B1D7-9A82747121B9@gmail.com>
To: "Tab Atkins Jr." <jackalmage@gmail.com>
Cc: fantasai <fantasai.lists@inkedblade.net>, Brian Manthos <brianman@microsoft.com>, "www-style@w3.org" <www-style@w3.org>
Whether or not the blur occurs entirely inside the box, outside the  
box, or half and half (as we now know it does, more or less), it is  
still a blur value that the author provides, and thus it is the blur  
effect that can and should be measured to see if it was rendered  
correctly. Regardless of your priorities, the number is supposed to  
represent an amount of blur, and that is what it should be equal to  
when rendered. Not half the amount of rendered blur.

On Jun 21, 2010, at 6:13 PM, "Tab Atkins Jr." <jackalmage@gmail.com>  

> On Mon, Jun 21, 2010 at 5:55 PM, Brad Kemper <brad.kemper@gmail.com>  
> wrote:
>> I liken it to PostScript, where a border is drawn down the center  
>> of a path:
>> half inside, and half outside. Sure, you may be interested in  
>> knowing how
>> much wider that border is going to make your box, but at the end of  
>> the day,
>> if you ask for a 19 point border, you get get a 19 point border,  
>> not a 38
>> point border. You don't have to specify 8.5 points to get a 19  
>> point border.
>> Because it is a border you are setting in PostScript, not a  
>> distance that
>> the border extends the box width on one side.
> My description of why I expect what I do should explain the
> difference.  For a border, you care about the whole thing.  The whole
> area is visible and important.  Thus, a length specified for the
> border width should apply to the whole thing.  That's fine and
> uncontroversial.  (SVG also works that way, btw.)
> Blur is different, because I simply don't care what sort of blurring
> it does inside the box.  Like I said, before this conversation I had
> no idea that the blur area was equal inside and outside.  In fact, I
> think I can go further than that - I'm pretty sure that I've never
> consciously realized that the blur goes into the box *at all*.  I
> mean, I certainly saw that the box was lighter just inside the normal
> area, but it never consciously struck me that "blur extends both ways
> from the box perimeter".  Like I said, as long as it looks pretty, I
> don't care about what the blur does inside the box.
> When I add a blur to something, my thoughts are "okay, now I want to
> blur this out 10 pixels" or sometimes "I want this blurred so that the
> total size of the thing + blur is 100px".  My thought processes and
> internal dialogue *explicitly* refer only to the length that the blur
> extends out of the current shape.
> That's fine that you always think about blur explicitly in terms of
> the size of the entire blur area.  I don't, and it appears several
> other people don't either.  I think about it in roughly the same way I
> think about spread.  It's possible that, had CSS used a stroke model
> rather than a border model, like SVG, I'd think differently.  But it
> doesn't, and I don't.
> ~TJ
Received on Tuesday, 22 June 2010 01:50:08 UTC

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