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First I show an example where what for the patch is good. Consider the
menger fractal constructed as follows:
macro menger(l,d)
#if (d>0)
#local p = menger(l/3,d-1) union{
#declare ix=-1; #while(ix<2)
#declare iy=-1; #while(iy<2)
#declare iz=-1; #while(iz<2)
#if ((ix!=0 & iy!=0) | (iy!=0 & iz!=0) | (ix!=0 & iz!=0))
object{p translate <ix,iy,iz>*l/3}
#end
#declare iz=iz+1; #end
#declare iy=iy+1; #end
#declare ix=ix+1; #end bounded_by{box{-l/2,l/2}}}
#else sphere{0,l/2} #end
#end
#declare myplane = plane{x,0 translate<-6,0,0> rotate <0,90,0> rotate
<45,-20,0>}
intersection{
object{menger(4,3) rotate <20,30,0> translate <0,0,10>}
object{myplane} // *
pigment{rgb 1}
}
light_source{<-100,200,-20>,1 }
This needs about 250s to render and the statistics say
Box 1417965 164676 11.61
CSG Intersection 82765 13615 16.45
CSG Union 164676 131410 79.80
Plane 82765 81320 98.25
Sphere 1958320 105681 5.40
Bounding Object 1417965 164676 11.61
But if you remove the line markes with an '*' it only needs 2 seconds and
gives:
Box 1422461 161254 11.34
CSG Intersection 83741 17944 21.43
CSG Union 161254 122553 76.00
Sphere 1886360 100982 5.35
Bounding Object 1422461 161254 11.34
You see that the number of test are nearly the same. Why does it take so
much longer then? Each time a ray hits the plane it tests if the
intersection point is inside the menger fractal. But it seems to do this
for *each single sphere*.
My patch changes this. It first tests if the point is inside the bounding.
If it is NOT then it knows that it can already decide that the point is
outside (if the object IS NOT inversed) or that the point is inside (if the
object IS inversed).
Therefore with my patch applied it needs only 2 seconds to render for *both
cases*.
- Micha
--
http://objects.povworld.org - the POV-Ray Objects Collection
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