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Re: [css3-images] Probably Editorial: radial-gradient() and concentric ellipses

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Wed, 29 Feb 2012 11:01:35 -0800
Message-ID: <CAAWBYDBU1w6rC4x7P2ivRY_cCqgQcBMYn-iov0yups6Fq6oyrA@mail.gmail.com>
To: Øyvind Stenhaug <oyvinds@opera.com>
Cc: "Kang-Hao (Kenny) Lu" <kennyluck@csail.mit.edu>, WWW Style <www-style@w3.org>
On Wed, Feb 29, 2012 at 10:22 AM, Øyvind Stenhaug <oyvinds@opera.com> wrote:
> On Wed, 29 Feb 2012 18:17:41 +0100, Kang-Hao (Kenny) Lu
> <kennyluck@csail.mit.edu> wrote:
>
>> (12/03/01 0:58), Øyvind Stenhaug wrote:
>>>
>>> On Tue, 28 Feb 2012 17:16:28 +0100, Tab Atkins Jr.
>>> <jackalmage@gmail.com> wrote:
>>>>
>>>> Yup, everyone does the obvious thing.  I've added the word
>>>> "proportional" in front of "concentric ellipses".  That sound good?
>>>
>>>
>>> I think you'd need a further restriction. As I understand it, a radial
>>> gradient consists of all ellipses E such that
>>> 1) E and the ending shape are concentric - that is, they have the same
>>> center
>>> 2) E and the ending shape have the same eccentricity - I assume this is
>>> what "proportional" means, though using that word when talking about
>>> two-dimensional shapes sounds unfamiliar to me (I didn't use the term
>>> "similar" since that has a non-mathematical meaning which is much more
>>> vague)
>>> 3) the major semiaxes/radii of E and the ending shape coincide
>>> (otherwise you'd include ellipses that are rotated by any arbitrary
>>> amount)
>>
>>
>> Well, in some sense "proportional" could be interpreted as "scaled
>> proportionally" (so no roation involved and hence it covers 3) ) so I
>> found Tab's tweak satisfactory. Most importantly, it doesn't seem to be
>> necessary to confuse readers with mathematicl terms like "eccentricity"
>> and "semiaxes/radii" when the interoperability problem this vagueness
>> might cause is pretty theoretical.
>
>
> Right, I didn't mean to suggest an actual wording, and I agree that it's a
> relatively minor and theoretical issue. (Though in general I think exactness
> should trump briefness and readability for non-technical readers, for the
> normative sections. I'd prefer not to have to interpret and guess what the
> writer meant.)
>
> How about "uniformly scaled" instead of "proportional"?

Based on this discussion, I've made a few tweaks to the wording.  I'm
using the term "uniformly-scaled" in a few places, and better define
the actual rendering of the gradient with the following paragraph:

"""
The color of the gradient at any point is determined by first finding
the unique ellipse passing through that point with the same center and
ratio between major and minor axises as the ending-shape. The point's
color is then the color of the gradient ray at the point where this
ellipse intersects it.
"""

Does this sound all right?

~TJ
Received on Wednesday, 29 February 2012 19:02:36 GMT

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