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

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Wed, 23 Jun 2010 08:17:40 -0700
Message-ID: <AANLkTikJa5s3gkOew9wY3vJNu6tlN7CBQP5oI4PltAhT@mail.gmail.com>
To: robert@ocallahan.org
Cc: Simon Fraser <smfr@me.com>, Brad Kemper <brad.kemper@gmail.com>, fantasai <fantasai.lists@inkedblade.net>, Brian Manthos <brianman@microsoft.com>, "www-style@w3.org" <www-style@w3.org>
On Tue, Jun 22, 2010 at 9:28 PM, Robert O'Callahan <robert@ocallahan.org> wrote:
> On Wed, Jun 23, 2010 at 3:08 PM, Tab Atkins Jr. <jackalmage@gmail.com>
> wrote:
>>
>> Interesting.  I'm really not seeing that.  Check out this test case, frex:
>>
>> <!DOCTYPE html>
>> <body style="font-size: 1000px; text-shadow: 0 0 100px black; color:
>> white; font-family: Arial, sans-serif;">
>> f
>> <div style="background: red; width: 100px; height: 3px; position:
>> absolute; top: 700px; left: 183px;"></div>
>>
>> (You may have to adjust the "left" on the <div>.)
>>
>> It seems very clear from a visual inspection that the blur only
>> extends outward roughly 50px.  This effect occurs on both my Windows
>> and Linux machines.
>
>
> With that testcase, there's a 79 pixel-wide shadow of
> not-completely-transparent pixels on both my Mac and Linux trunk builds.
> Certainly some of those pixels are not apparent to the naked eye :-) ... a
> screen magnifier that displays the actual color values of selected pixels is
> useful.

Oh, jeez.  I was looking at webkit's rendering twice, rather than
looking at webkit and then firefox.  I feel silly.  You're correct -
for a 100px blur, the shadow extends outward 79px.

That still doesn't explain Simon's statement that the blur extends
outward by the full blur length.  I continue to measure a nearly
perfect half-blur-length of shadow extending from the main shadow body
in Chrome, whether the blur is 8px or 100px.

~TJ
Received on Wednesday, 23 June 2010 15:18:32 GMT

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