On Wed, 6 Feb 2002 11:53:21 -0500, "cadman" <cad### [at] graffitinet>
wrote:

>The docs say that the cylinder light syntax is exactly like the spotlight
>syntax.

It is.

>How can this be so?

Because they act exactly the same from the point of emission to the
point_at point.

>The radius keyword in the spotlight is the radius angle of the cone 
>surface from the reflective vector.  There is no such thing for a cylinder.

There is, it is the visible angle, as seen from the point of emission,
of the cross-section of the cylinder containing the point_at point.
Simple, eh? :))

>Same with the falloff keyword.

Exactly.

>What effect do these keywords have on a cylinder light?  When toying with
>it, it seems that the falloff has the most effect on the look of the light,
>and radius seems to have no effect.  Anyway, you get the idea.  How is the
>cylinder light supposed to be used?

A cylinder light *is* a spotlight, from the point of view of
controlling parameters and lighting behaviour. The only difference is
that the cone of light is trimmed with an infinite cylinder, but this
does not affect the light distribution within it. The axis of this
cylinder is colinear with the vector between the emission point and
point_at, and the radius of the cylinder is exactly the radius of the
cone at its focal plane (if that could be said for a spotlight :) )

If my babblings make it more clear, then the docs could use a
refreshment.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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