"Pov-Ray Dummy" <nomail@nomail> wrote:
> [...] I would like them to rotate to make them appear to
> roll instead of just 'sliding'.

A broad approximation would be to find the distance that the centre of the ball
has moved since the previous frame, and rotate the ball (in degrees) by "z *
360 * distance / radius". This would slip slightly if the curve was tight, but
the calculation is easy to understand and do on a 2D curve when you know the
animation path. If the can't create the path directly, you'd need to make an
'inset path' from the curved surface, and make that your animation path.

Then there's a physics-based approach, which would be a lot more accurate. I
don't really have the skill nor patience to describe that here :o)

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