gadoid nous apporta ses lumieres en ce 2007/09/06 16:11:
> The code below generates five spheres which should be invisible, yet three
> of them are visible from their interaction with the environment.  The
> spheres become visible when you apply a rotation to a texture that uses a
> texture_map  containing clear (rgbt <1,1,1,1>) components as in the
> T_Electron texture below.  If the texture is not rotated, then the sphere
> remains invisible.  Rotation applied to a clear texture not part of a
> texture_map also remains invisible.
> 
> It also seems to be the case that the surface behind the spheres must have a
> "normal" for the effect to occur.  The effect goes away if you remove the
> "normal" block in the texture of the  "floor".
> 
> I realize the T_Electron texture as written below is pretty pointless, but
> in the actual scene I am trying to create, not all of the texture map is
> clear. The intent was to create a spherical shell of lightning with parts
> of the texture_map representing the lightning, and the rest clear.  The
> problem I am having is the the clear portions affecting the appearance of
> objects behind it.  I removed the "lightning" portion for this example.
> 
> I am using povray 3.6
> 
> #include "colors.inc"
> 
> #declare T_Clear = texture {pigment { Clear }}
> 
> #declare T_Electron =
>   texture {
>     crackle
>     texture_map {
>         [0.00   T_Clear]
>         [1.00   T_Clear]
>     }
>   }
> 
> //
> // Three of these spheres are visible (those at x positions -1,
> // 0 and 1).
> //
> sphere { <-1,1,0>,   0.2 hollow texture { T_Electron rotate 90*y }}
> sphere { <-0.5,1,0>, 0.2 hollow texture { T_Electron rotate 0*y }}
> sphere { <0,1,0>,    0.2 hollow texture { T_Electron rotate 90*y }}
> sphere { <0.5,1,0>,  0.2 hollow texture { T_Clear rotate 90*y }}
> sphere { <1,1,0>,    0.2 hollow texture { T_Electron rotate 90*y }}
> 
> 
> plane { y, 0
>   texture {
>     pigment {
>       checker
>       Red
>       White
>       scale 0.05
>     }
>     normal { bozo 4}
>   }
> }
> 
> light_source {
>   <-8.0,   6,   -10>
>   color rgb 2
> }
> 
> camera {
>   //
>   // New Main view
>   //
>   look_at <0,1,0>
>   location <0,1.5,-2>
> 
>   up <0,1,0>
> }
> 
> 
> 
> 
> 
Strange. After playing with the rotation, it apears that the effect is affected 
by the amount of the rotation, as well as the axis of the rotation. At rotation 
90, 60 and 30 give me the most effect.

-- 
Alain
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