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

From: Simon Fraser <smfr@me.com>
Date: Fri, 11 Jun 2010 15:44:27 -0700
Cc: Brad Kemper <brad.kemper@gmail.com>, "L. David Baron" <dbaron@dbaron.org>, Brian Manthos <brianman@microsoft.com>, "www-style@w3.org" <www-style@w3.org>
Message-id: <7AE2A002-1075-42D0-92FF-7090778289D4@me.com>
To: fantasai <fantasai.lists@inkedblade.net>
On Jun 11, 2010, at 3:18 PM, fantasai wrote:

> On 06/11/2010 02:03 PM, Brad Kemper wrote:
>> On Jun 11, 2010, at 11:13 AM, Simon Fraser <smfr@me.com> wrote:
>> 
>>> I don't think the current definition, which describes the blur in
>>> terms of a gradient, is good for shapes with concave portions.
>> 
>> I don't know why not. It doesn't say it's a gradient, it just defines
>> the size of the region to blur within. I think that saying that a 15px
>> blur covers a perimeter that is 15px wide will be a whole lot more
>> understandable and predictable and meaningful for authors than to ask
>> them to guess how much that will be based on the results of plugging
>> that length into a guassian function.
> 
> What Simon is trying to say is that it's not a straight-up transition
> of 15px.
> 
> If I'm understanding this correctly (I'm shooting in the dark here),
> the Gaussian function, when applied to concave shapes like the inside
> of a corner, will result in an effective "radius" that is much larger
> at certain points. This is in fact what you want: otherwise the corner
> doesn't look blurred, it looks gradient-ed.
> 
> Imagine a sharp concave corner (i.e. the border with an inner shadow).
> If you put a true Gaussian blur on that, the edge where the shadow
> finally disappears will have a slight curve.
> 
>     +--------------     [ I lack hixie's awesome ascii art skillz,
>     |                     but I'm trying here... ]
>     |         _____
>     |      ,'
>     |     :
>     |     |
>     |     |
> 
> In the current definition, you'll get a sharp edge.
> 
>     +--------------
>     |
>     |      ________
>     |     |
>     |     |
>     |     |
>     |     |
> 
> If I'm understanding this correctly, applying a true Gaussian and
> then thresholding it will probably fix those weird kinks you were
> seeing on inner shadow spreads with the current definition.

Yes, this is exactly the issue.

Simon
Received on Friday, 11 June 2010 22:45:21 GMT

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