Render the scenes in this post with +UD so you can see the Vista Buffers,
and have an idea of where the bounding boxes of the objects are.

This scene has no problems:

camera {location <-10,10,-10> look_at 0}
light_source {<-100,100,-100> rgb 1}

// 2 identical sphere sweeps:
sphere_sweep {
 linear_spline,
 4,
 40, .1
 50, .1
 60, .1
 70, .1
}
sphere_sweep {
 linear_spline,
 4,
 40, .1
 50, .1
 60, .1
 70, .1
}

However, when we introduce one more sphere_sweep to the scene, identical to
the other two...

camera {location <-10,10,-10> look_at 0}
light_source {<-100,100,-100> rgb 1}

// 3 identical sphere sweeps:
sphere_sweep {
 linear_spline,
 4,
 40, .1
 50, .1
 60, .1
 70, .1
}
sphere_sweep {
 linear_spline,
 4,
 40, .1
 50, .1
 60, .1
 70, .1
}
sphere_sweep {
 linear_spline,
 4,
 40, .1
 50, .1
 60, .1
 70, .1
}

The third sphere_sweep insists that its bounding box contains the point
<0,0,0>, even though none of the sphere_sweeps come even close to that
point. Again, render with +UD in order to see this fact.

Note that the sphere_sweeps don't have to be entirely coincident for the bug
to occur. I discovered it in a scene where each sweep touched each other at
two of the four points. (The bug still occurs if you reduce the number of
points in each sphere_sweep.)

(Oh! Just discovered! They don't have to be coincident at *all* - the
following scene also produces the error:
camera {location <-10,10,-10> look_at 0}

light_source {<-100,100,-100> rgb 1}

sphere_sweep {
 linear_spline,
 2,
 40, .1
 50, .1
}
sphere_sweep {
 linear_spline,
 2,
 60, .1
 70, .1
}
sphere_sweep {
 linear_spline,
 2,
 90, .1
 100, .1
}

)

I hope this hasn't already been reported.

- Slime
[ http://www.slimeland.com/ ]
[ http://www.slimeland.com/images/ ]

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