Le 18-03-27 à 23:30, Sven Littkowski a écrit :
> Thanks Alain and Stephen.   :-)
> 
> The item is what is to be checked for (like the name of a Declare union,
> I would assume).
> 
> The first coordinate is from where the search ray is starting?
> 
> The second coordinate is towards which direction (destination) the
> search ray is heading?
> 
> Norm contains the coordinates of a hit?
> 
> 
> ---
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The correct way to use trace with an arbitrary, oddly shaped, target 
object is :
#declare Normal =<0,0,0>;
#declare SurfacePoint= trace(<PosX, 1000, PosZ>, -y, Normal);
#if(vlength(Normal))
	...do your stuff...
#end

"SurfacePoint" will contain the location of the point directly under 
<PosX,1000,PosZ>, or <0,0,0> it the trace miss the object. As a 
legitimate point may be at that location, this is not a reliable way to 
know if the trace hit or not.
"SurfacePoint" contain the location that interest you.

If the trace miss the target object, Normal have a zero length. If it 
find the object, Normal contain the normal of the surface at that point 
as an a unit length vector.


Alain

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