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RE: [css3-background] color transition line

From: Brian Manthos <brianman@microsoft.com>
Date: Tue, 1 Nov 2011 08:43:17 +0000
To: fantasai <fantasai.lists@inkedblade.net>, "www-style@w3.org" <www-style@w3.org>
Message-ID: <9710FCC2E88860489239BE0308AC5D1704415685@TK5EX14MBXC266.redmond.corp.microsoft.com>
Ok, I think we're interpreting the 3rd sentence differently.

> # The line demarcating this
> # transition is drawn between the point at that angle on the outer arc
> # and the point at that angle on the inner arc.

I read "that angle" as referring to the 45deg / 30deg in the preceding sentence, and the phrasing in the 3rd sentence as meaning "draw a line segment connecting where that line meets the inner arc/point and the outer arc".

I think you're reading it as "use the angle an indicator of the location along the partial ellipse of the outer curve, do the same with the inner curve, and connect the dots".


Perhaps my interpretation is the less common interpretation.


That said, upon further inspection referring to the "inner arc" at all is folly since sometimes it's a point not an arc and thus it's just confusing at best.


Perhaps we should just strike the 3rd sentence entirely.  Is that the proposal?


-Brian

> -----Original Message-----
> From: fantasai [mailto:fantasai.lists@inkedblade.net]
> Sent: Tuesday, November 01, 2011 12:55 AM
> To: www-style@w3.org
> Subject: Re: [css3-background] color transition line
> 
> On 10/31/2011 09:15 PM, Brian Manthos wrote:
> > Also, I thought the spec was pretty clear on this topic in section
> 5.4:
> 
> It is, and it's wrong. See previous message.
> 
> > http://www.w3.org/TR/css3-background/#corner-transitions
> > # The center of color and style transitions between adjoining borders
> > # is at the point on the curve that is at an angle that is
> proportional
> > # to the ratio of the border widths. For example, if the top and
> right
> > # border widths are equal, that point is at a 45 angle from the
> > # horizontal, and if the top is twice the width of the right the
> point
> > # is at a 30 angle from the horizontal. The line demarcating this
> > # transition is drawn between the point at that angle on the outer
> arc
> > # and the point at that angle on the inner arc.
> >
> > IE9's implementation matches this conformance requirement.
> 
> No, it doesn't. It matches the first rendering in this set:
>    http://lists.w3.org/Archives/Public/www-archive/2011Jul/0005.html
> But the spec is the third one.
> 
> > In your sample (0005.html), it appears that you are using consistent
> width
> > across all 4 sides of the border.
> 
> Yes.
> 
> > As such, the correct rendering would have a color split along 45 deg
> angle
> > in the upper right corner.  Your first rendering looks like it might
> be
> > matching that, but I didn't pixel verify.
> 
> No, you're missing the last sentence in the spec. It's not drawn at a
> 45deg
> angle. The 45deg ray is used to find the intersection point on the
> inner
> and outer curves, and the line segment drawn between them is the
> transition
> line.
> 
> > While interesting to look at, the border-radius has no impact on the
> angle
> > at which the color transitions.  That's been my understanding since
> the
> > very beginning of working on CSS3 backgrounds in IE.  In fact we have
> > internal test cases to verify that this doesn't break accidentally.
> >
> > Has something changed since the spec went CR in February 2011 that
> necessitates
> > revisiting this?
> 
> The thing that's changed is that I've spent more time on this with an
> implementer,
> and thereby
>    a) noticed that the definition in the spec (the third one) can give
> results
>       that are totally wonky
>    b) found the answer that people seem to agree is the right one
> 
> ~fantasai
> 
Received on Tuesday, 1 November 2011 08:50:53 GMT

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