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[css3-2d-transforms] animation of skewX(), skewY(), skew()

From: L. David Baron <dbaron@dbaron.org>
Date: Wed, 2 Dec 2009 11:58:13 -0800
To: www-style@w3.org
Message-ID: <20091202195813.GA20179@pickering.dbaron.org>
http://dev.w3.org/csswg/css3-2d-transforms/#animation says that an
animation of skewX(), skewY(), or skew() is animation in the space
of angles.

In other words, it says that the midpoint (along the transition
function, not necessarily in terms of time) of an animation between
skewX(0) and skewX(60deg) is skewX(30deg).

I think it would make more sense if the animation of these functions
were in the space of the tangent of the angles (which seems like
it's a common representation of such transformations, see, e.g.,
http://en.wikipedia.org/wiki/Shear_mapping ).  In other words, the
midpoint of the animation between skewX(0) and skewX(60deg) should
be skewX(40.8934deg), because at this angle any point is transformed
to a position halfway between where it would be at skewX(0) and
where it would be at skewX(60deg), since atan(tan(60deg)/2) ==
40.8934deg.

-David

-- 
L. David Baron                                 http://dbaron.org/
Mozilla Corporation                       http://www.mozilla.com/
Received on Wednesday, 2 December 2009 19:58:50 GMT

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