Dave VanHorn nous apporta ses lumieres en ce 2007/07/06 17:13:
> That got it.
> 
> I had to step back a bit though, as it wouldn't let me do the differencing
> with pre-defined shapes.
> 
> IOW, the example you showed works fine, but if I declare a hole and try to
> difference it as below, I wasn't able to get that to work:
> 
> #declare Hole = object { cylinder {
> 0,(x*Ball_Dia),((Cam_Lens_Dia+(30*Mil))/2)
>                          rotate <0,0,(0 - Cam_Angle)>
>                          rotate <0,180,0>   //Around the vertical axis
>                        }
> 
> #declare Top = difference { sphere { <0,0,0>, (Ball_Dia/2) }
>                             sphere { <0,0,0>, ((Ball_Dia/2) - Wall_Thick)}
>                             Hole
>                             plane{-y,0}
>                             material { White_Plastic }
>                             photons { target 1.0 refraction on reflection on
> }
>                          }
> 
> 
> I'm also not convinced that I have the photons working right..  Photons seem
> to behave differently for a union or difference than they do if I take the
> objects that would have been in the union, and do them separately.
> 
> 
> 
> 
When you have a solid spherical object, it cause the light to converge. If you 
have one that have a hole in it's center, the cause light to DIVERGE.
So, if in this case photons apears to act that way, it's the physicaly correct 
behaviour.
Light coming trough the edges without encountering the empty space will converge.
Light that encounter the inner space at a low angle will get reflected outward 
by total internal reflection.
Light that enter that space will be affected as by a divergent lense. ( I did 
make extensive testing of that case )

If you use an union, photons will be affected by the interior surfaces, use a 
merge to remove those.

In every cases, make sure that you don't have coincident surfaces. Make a 
differenced or intersecting object slightly larger so that it protude slightly 
from the parent object.

-- 
Alain
-------------------------------------------------
Episcopalian: It's not so bad if shit happens, as long as you serve the right 
wine with it.

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