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Re: [CSS3, Backgrounds and Borders Module] some questions about border-radius

From: Zack Weinberg <zweinberg@mozilla.com>
Date: Sat, 22 Aug 2009 22:10:39 -0700
To: Andrew Fedoniouk <news@terrainformatica.com>, W3C Emailing list for WWW Style <www-style@w3.org>
Message-ID: <20090822221039.7acb6c51@trurl>
Andrew Fedoniouk <news@terrainformatica.com> wrote:
> "The transition must be contained within the segment of the border
> where the tangent of the inner curve either not defined or is not
> parallel with the sides of the box."
> It is not clear what does "tangent of the inner curve not defined"
> mean exactly. Is it an attempt to define case #9 here? :
> http://www.terrainformatica.com/w3/round-corners-sciter.png
> (case: width of borders is larger than border radius)

That's how I read it.  The tangent is undefined at a sharp corner.
Thus, in your case #9, the gradients can extend to the points where the
outer and inner edges become parallel lines again.

Perhaps that's better wording?  Something like

  The transition may not include any region of the border which is
  visually "side" rather than "corner": formally, the transition may
  not include any region where the inner and outer edges are parallel
  straight lines.

I'm having trouble coming up with words that are both unambiguous and
plain, so I think a diagram would be helpful; maybe something like the
attached SVG file.

> I believe that the only reasonable type of gradient here is so called 
> conic gradient. Probably it makes sense to define just that?

I'd call that out of scope for Level 3.  There are several shipping
implementations that do sharp transitions.


(image/svg+xml attachment: corner-transition-diagram.svg)

Received on Sunday, 23 August 2009 05:12:33 UTC

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