I was experimenting with a small macro which creates a mesh shaped like
a lathe from a spline. (The advantage of meshes over lathes is speed. Another
one is that with lathes you sometimes get artifacts which you don't get with
meshes.)

  This should demonstrate what does the macro do:

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#macro MakeEvenSplinePoints(Points)
  #local Amnt = dimension_size(Points, 1)-1;
  #local Ind = 0;
  #while(Ind <= Amnt)
    Ind/Amnt, Points[Ind]
    #local Ind = Ind+1;
  #end
#end

#declare Points = array[18]
{ <0,.1>,<1,0>,<1.2,.05>,<1,.1>,<.2,.3>,
  <.25,.4>,<.1,.9>,<.1,2.5>,<.3,2.8>,<.3,3.1>,
  <1,3.25>,<1.25,4>,<1,5>,<.9,5>,<1.1,4.5>,
  <1.15,3.8>,<1,3.4>,<0,3.2>
}

#declare Spline = spline { cubic_spline MakeEvenSplinePoints(Points) }

camera { location -z*14 look_at 0 angle 35 orthographic translate y*2.5 }
light_source { <100,200,-300>, 1 }
light_source { <-100,20,-30>, <1,.5,0>*.5 }
plane { -z,0 pigment { checker rgb 1, rgb .5 } }

// Final mesh:
object
{ MeshLathe(Spline, 80, 20)
  no_shadow
  pigment { rgb 1 } finish { specular .5 }
  translate x*3
}

// Mesh with flat triangles:
#declare MeshLatheDebug=3;
object
{ MeshLathe(Spline, 80, 20)
  no_shadow
  pigment { rgb 1 } finish { specular .5 }
}

// Spline preview with normals:
#declare MeshLatheDebug=2;
#declare MeshLatheDebugNormalColor=x;
object
{ MeshLathe(Spline, 80, 20)
  no_shadow
  pigment { rgb x+y } finish { specular .5 }
  translate x*-3
}
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Attachments:
Download 'MeshLatheDebug.jpg' (53 KB) Download 'MeshLatheExample.jpg' (23 KB)

Preview of image 'MeshLatheDebug.jpg'

Preview of image 'MeshLatheExample.jpg'