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

From: Kang-Hao (Kenny) Lu <kennyluck@csail.mit.edu>
Date: Thu, 01 Mar 2012 01:17:41 +0800
Message-ID: <4F4E5DB5.8090700@csail.mit.edu>
To: Øyvind Stenhaug <oyvinds@opera.com>
CC: WWW Style <www-style@w3.org>
(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. 

> (I also think that the orientation of the ending shape's axes is only
> implicitly given near the very end of "4.2.1.  radial-gradient() Syntax"
> - before that it seems to be taken for granted that they are
> horizontal/vertical.)

Agreed. In particular, the orientation is not well-defined for ellipses
that don't take explicit lengths but a keyword.

Received on Wednesday, 29 February 2012 17:18:15 UTC

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