In article <web.3fbfd9e59a8fede7cf187cb30@news.povray.org>,
 "stoecher" <sto### [at] gmxat> wrote:

> But there is a problem with shadows,
> as can be seen in the scene below.
> Is this a bug in povray?

Not a bug. Objects do not shadow light from a projected_through light 
until it hits the projected_through object. The light still comes from a 
single point, so while the positive light is getting shadowed, the 
negative light is constantly leaking through the projected_through 
planes past the shadowing object. Parallel lights will partially fix 
this problem:

light_source {LaserPoint, Red
    parallel point_at -z
}
light_source {LaserPoint, -Red
    parallel point_at -z
    projected_through {
        plane {z, 20 clipped_by {union {plane {-y,-0.3} plane {y,-0.3}}}}
    }
}

However, they introduce a new one...all light rays are parallel, rather 
than originating from a vertical line. This will affect shading and 
shadowing, but may not be noticeable. You could approximate a "spread" 
light by using multiple spot lights combined with this technique...

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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