Carl Hoff e-mailed this to me:
> Ok... I see what you are doing now I think.  To be honest I want the
> effect to continue around corners a little so I can work with that.  The
> main problem I'm having isn't with the effect at the head of the trail.
> That will be moving with the bike.  Where I'm having the hardest time
> with is simply how to draw the trail.  Its fixed in position and growing.
> I can of course break each line segment into its own little animation
> and deal with it that way but say I wanted to animate your sphere
> sweep having it start with zero length till it covered the whole path at
> the end.  I can animate a sphere moving along a linear_spline but
> at present I'm not sure how to animate a sphere moving along a
> linear_spline leaving the bent cylinder behind it.  The other issue I
> see coming (I'm not to this point yet) but lets say the object I'm
> animating along the linear_spline isn't a sphere but it has a defined
> front and back.  At a given point along the linear spline how do I
> define forward?  And to take this one dimension farther if the cycle
> can drive up walls how do I define up?
And I'm posting it here so I don't get backed into a corner (pun intended)
alone while trying to help him.

Hi Carl.

Well, glad you explained that this is about tacking a trail start down and
stretching it along from there. I wasn't catching onto that idea at all,
before now. I was only thinking of a blur left behind the bike. Looking at
TRON DVD on shelf and it doesn't even show any of that, must see movie
again.

Growing the trail along as the bike moves... guess that could be done...
maybe by giving the sphere_sweep the number of points as 'frame_number'. Or
at least some integer based on it. Then the points could be gathered from an
'array', previously set up, invoking them via a 'while' loop which uses the
point count to pull them out of the array.

Make sense? Gee, I hope somebody else out there knows what we're talking
about and has some ideas too. I never became a wizard at using arrays in
POV. Thinking it over, I'm not so sure it could be done this way.

What you asked about the front/back or leading/trailing sides is simply a
matter of pulling a vector from out of the spline by its time (or t) value.
Such as I did to place the light_source ahead of center. It's just any
amount +/- of the clock, in that example. And then the question about going
up walls would be done by adding y values to the sphere_sweep and spline
vectors.

-- 
Bob H.
http://www.3digitaleyes.com

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