Hello all,

this is my first time posting here, even though I've been using POVRay on and
off for quite a few years. I'm currently using version 3.7 as shipped by Debian
(sid), I believe I have a found a configuration where the no_image tag is
ignored for a union member when the union itself is inside a difference. A repro
is the following:

--- 8< -----

#version 3.7;

#include "colors.inc"

#declare Wall = box {
 <-100, 0, 0>
 < 100, 100, 5>
}

#declare Pair = union {
 object { Wall translate 100*z no_image on }
 object { Wall translate 200*z }
}

difference {
 object { Pair }
 box { <0, 0, 0> <0, 0, 0> }
 pigment { color White }
}

light_source {
 <200, 200, -10>
 color White
}

camera {
 location <0, 200, 0>
 look_at  <0, 100, 100>
}


--- 8< -----


illustrate the odd behavior: both walls are rendered. Replacing the `difference`
with a direct use of the object `object { Pair pigment { color White } }` works
as expected, as does using a union instead of a difference (in both cases, a
single wall is visible, albeit with a shadow cast from the other, invisible
wall).

I'm not entirely sure if this behavior is expected or a bug. In the latter case,
should I open a GitHub issue?

Best regards and thanks for your patience,

Oblomov

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