Peter Popov wrote in message <375a9e93.26520084@news.povray.org>...
>
>No, the _plane_ of twirling is perpendicular to this 3-points-defined
>plane, not the _normal vector_ of the twirl.
>


But there can be an infinite number of such planes. You mean the one facing
the camera?
OK, but this would still look weird if the surface is at a shallow angle
towards the camera, i.e. the axis of rotation is near-parallel to the
surface. Since the warp would actually still be cylindrical, this would
result in a blocky gradient displacement of colur, not a "whirlpool"
pattern.
I believe a user-defined axis of twirl would be the best way to go; I can
think of no efficient way of taking into account surface topography when
applying a basically 2D pattern to a 3D surface.

Margus

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