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Re: [CSSWG] Minutes and Resolutions 2009-02-04: box-shadow and border-image

From: Brad Kemper <brad.kemper@gmail.com>
Date: Tue, 17 Feb 2009 22:19:43 -0800
Cc: fantasai <fantasai.lists@inkedblade.net>, "www-style@w3.org" <www-style@w3.org>
Message-Id: <57E61D77-9174-40E8-9A2C-FEFA2D5D8EE8@gmail.com>
To: "Tab Atkins Jr." <jackalmage@gmail.com>

On Feb 17, 2009, at 2:13 PM, Tab Atkins Jr. wrote:

>>> Using manhattan distance is like using a square brush.  Lines stay
>>> lines, curves stay curves, but corners *stay* corners.
>>
>> Isn't that only true if the corners are horizontal and vertical lines
>> that intersect at 90deg angles? If I outline a star with a square  
>> brush,
>> the top point looks like this:
>>
>>                    ______
>>                   /      \
>>                  /        \
>>                 /    /\    \
>>                /    /  \    \
>
> Huh.  Yeah, you're right.  Don't know why I didn't see that
> immediately.  And since applying a manhattan distance metric really
> *is* just like tracing it with a square brush, this is exactly what
> would result.

The way I see it, you're either going to have chunky, brush-shaped  
corners somewhere where you don't want them, or nice round corners  
that computer artists are used to, especially for shadows with spread.  
The latter (round corners) is what you get with PhotoShop spread  
shadows.

By the way, the term "spread" in this sense was previously applied to  
a technique used for trapping [1] when printing two solid colors next  
to each other, and the term predates digital trapping techniques that  
also use spreading. In PostScript, such as when using Adobe  
Illustrator, etc., you could get a spread by stroking a vector path  
with the same color as the background, and then setting it to  
overprint whatever object was behind it. I was doing that in the very  
late 80s, as I recall, with Illustrator 88. Because it was a vector  
path, you could get nice sharp corners, round corners, chopped off  
corners, or corners that were sharp when greater than a certain angle  
and chopped off otherwise. But before that, spreads and chokes were  
created through diffusion through pieces of film, and as a result the  
corners were always rounded.

[1] http://en.wikipedia.org/wiki/Spreading_and_choking
Received on Wednesday, 18 February 2009 06:20:21 GMT

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