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

From: fantasai <fantasai.lists@inkedblade.net>
Date: Fri, 11 Jun 2010 15:18:40 -0700
Message-ID: <4C12B640.3040301@inkedblade.net>
To: Brad Kemper <brad.kemper@gmail.com>
CC: 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 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.

~fantasai
Received on Friday, 11 June 2010 22:19:19 GMT

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