/*
 ====================================================
 The Hall effect in metal under various circumstances
 ----------------------------------------------------
 Created by Søren Peo Pedersen - see my user page at
 http://da.wikipedia.org/wiki/Bruger:Peo
 ====================================================
 */
 
 #declare NorthAtLeft=no; // Orientation of magnetic field:
 // Use "yes" for north pole to the left, and south pole to the right
 // Use "no" for north pole to the right, and south pole to the left
 
 #declare PlusTowardsViewer=yes;  // Direction of current:
 // Use "yes" to have the positive pole at the ends of battery and Hall sensor nearest to viewer
 // Use "no" to have the negative pole at the ends of battery and Hall sensor nearest to viewer
 
 #declare PositiveCharge=no; // Polarity (color) of charge carriers in the circuit:
 // Use "yes" for orangeish colored charge carriers in wires and Hall sensor
 // Use "no" for light blue colored charge carriers in wires and Hall sensor
 
 #declare HallUpwards=yes; // Direction of sideways force upon charge carriers:
 // Use "yes" to have the charge carriers "bend upwards" inside Hall element
 // Use "no" to have the charge carriers "bend downwards" inside Hall element
 
 #declare NegativeEdgeUp=yes;  // Electrical polarization of Hall element (indicated by color):
 // Use "yes" to have bluish color at top of Hall element, indicating negative charge here
 // Use "no" to have reddish color at top of Hall element, indicating positive charge here
 
 #declare MagnetFont="arialbd.ttf" // Font for the "N" and "S" nomenclature on magnets
 
 // -----------------------------------------------------------------------------------------
 
 #declare txtNeutralElement=texture {  // Texture for electrically neutral parts of Hall element
   pigment {color rgbft <.5,.5,.5,1,0>}
   finish {
     reflection rgb .5
     phong 1
     metallic
     }
   }
   
 #declare txtNegativeElement=texture { // Texture for negatively charged parts of Hall element
   pigment {color rgbft <.1,.3,.9,1,0>}
   finish {
     reflection rgb <.1,.3,.9>
     phong 1
     metallic
     }
   }
   
 #declare txtPositiveElement=texture { // Texture for positively charged parts of Hall element
   pigment {color rgbft <.9,.3,.1,1,0>}
   finish {
     reflection rgb <.9,.3,.1>
     phong 1
     metallic
     }
   }
 
 #declare txtPolarisedElement=texture {  // Texture for polarized parts of the Hall element
   gradient y
   texture_map {
     [0 txtNegativeElement]
     [.5 txtNeutralElement]
     [1 txtPositiveElement]
     }
   translate <0,-.5,0>
   #if (NegativeEdgeUp)
     rotate <180,0,0>
   #end
   }
 
 #declare txtHallElement=texture { // Complete texture for the entire Hall element
   gradient z
   texture_map {
     [0 txtNeutralElement]
     [.5 txtPolarisedElement]
     [1 txtNeutralElement]
     }
   translate <0,0,-.5>
   scale 4
   }
 
 #declare WireTxt=texture {  // Texture for the wires connecting Hall element with power source
   pigment {color rgb .5}
   finish {
     reflection rgb .7
     phong 3
     metallic
     }
   }
 
 #declare Qtorus=intersection{   // 1/4 of a torus, for rounded "corner" on the wiring
   torus {1,.06 rotate <0,0,90>}
   box {-2,<2,0,0>}    
   }
 
 #declare PlusPgmt=pigment {   // Pigment for positive end of the battery (power source)
   object {
     merge {
       box {<-.3,0, .35>,<.3,1,.45>}
       box {<-.05,0, .1>,<.05,1,.7>}
       }
     pigment {color rgb <1,0,0>}
     pigment {color rgb 1}
     }
   }
 
 #declare MinusPgmt=pigment {  // Pigment for negative end of the battery (power source)
   object {        
     box {<-.3,0,-.55>,<.3,1,-.45>}
     pigment {color rgb <0,0,1>}
     pigment {color rgb 1}
     }
   }
 
 #declare PowerSource=union {  // Power source, symbolised by a battery
   merge {
     torus {.45,.05 rotate <90,0,0> translate <0,0,-.95>}
     cylinder {<0,0,-.95>,<0,0,.8>,.5}
     torus {.45,.05 rotate <90,0,0> translate <0,0, .8>}
     pigment {
       object {
         plane {<0,0,1>,0}
         pigment {PlusPgmt}
         pigment {MinusPgmt}
         }
       rotate <0,0,-35>
       }
     finish {ambient .4}
     }
   merge {
     torus {.35,.05 rotate <90,0,0> translate <0,0,-.95>}
     cylinder {<0,0,-1>,<0,0,-.9>,.35}
     torus {.35,.05 rotate <90,0,0> translate <0,0,.8>}
     cylinder {<0,0,.85>,<0,0,.8>,.35}
     difference {
       cylinder {<0,0,.85>,<0,0,.9>,.15}
       torus {.15,.05 rotate <90,0,0> translate <0,0,.9>}
       }
     cylinder {<0,0,.9>,<0,0,.95>,.1}
     torus {.05,.05 rotate <90,0,0> translate <0,0,.95>}
     cylinder {<0,0,.95>,<0,0,1>,.05}
     pigment {color rgb .5}
     finish {reflection rgb .9 phong 1 metallic}
     }
   }
 
 #macro txtChargeCarrier(Transparency) // Texture for charge carriers and their "motion blur tails"
 pigment {color rgbt <
   #if (PositiveCharge)
   1,.5,.2,Transparency
   #else
   .2,.5,1,Transparency
   #end
   >}
 finish {ambient .4}
 #end
 
 #declare FieldArrow=merge {   // Arrow indicating direction of magnetic field
   cylinder {<-2.5,0,0>,<2.3,0,0>,.003}
   cone {<2.3,0,0>,.05,<2.5,0,0>,0}
   pigment {color rgb 0}
   #if (NorthAtLeft)
   #else
   scale <-1,1,1>
   #end
   no_shadow
   no_reflection    
   }
 
 #declare StraightCharge=union {   // Charge carrier with straight "motion blur tail"
   sphere {0,.15 texture {txtChargeCarrier(0)}}
   cylinder {0,<0,0,.499>,.15 hollow
     texture {
       gradient z
       texture_map {
         [0 txtChargeCarrier(0)]
         [1 txtChargeCarrier(1)]
         }
       scale .5
       }        
     }
   no_shadow
   no_reflection
   }
 
 #declare CurvedCharge=union {   // Charge carrier with curved "motion blur tail"
   sphere {<0,-1,0>,.15 texture {txtChargeCarrier(0)}}
   difference {
     torus {1,.15 rotate <0,0,90>}
     plane {<0,0,1>,0}
     plane {<0,0,-1>,0 rotate <-29.99,0,0>}
     hollow
     texture {
       radial
       texture_map {
         [0 txtChargeCarrier(.3)]
         [1 txtChargeCarrier(1)]
         }
       frequency 12
       rotate <0,0,90>
       }
     }
   no_shadow
   no_reflection
   }
 
   // The scenario:  
   box {<-.16,-1,-2>,<.16,1,2>   // The hall element
     texture {txtHallElement}        
     no_shadow
     }
   
   merge { // Wiring with travelling charge carriers
     // Wiring on the side towards the viewer:
     cylinder {<0,0,-2>,<0,0,-3>,.06}
     #object {Qtorus rotate <90,0,0> translate <0,-1,-3>}
     cylinder {<0,-1,-4>,<0,-2,-4>,.06}
     #object {Qtorus translate <0,-2,-3>}
     cylinder {<0,-3,-3>,<0,-3,-1>,.06}
     // Wiring on the side facing away from the viewer:
     cylinder {<0,-3, 1>,<0,-3, 3>,.06}
     #object {Qtorus rotate <-90,0,0> translate <0,-2,3>}
     cylinder {<0,-1, 4>,<0,-2, 4>,.06}
     #object {Qtorus rotate <180,0,0> translate <0,-1,3>}
     cylinder {<0,0, 2>,<0,0, 3>,.06}
     texture {WireTxt}
     }
 
   union { // Charge carriers:
     // Charge carriers on the side towards the viewer:
     #object {StraightCharge translate <0,-3,-2.7>}
     #object {CurvedCharge rotate <30,0,0> translate <0,-2,-3>}
     #object {CurvedCharge rotate <90,0,0> translate <0,-2,-3>}
     #object {StraightCharge rotate <90,0,0> translate <0,-1,-4>}
     #object {StraightCharge rotate <90,0,0> translate <0,-1,-4>}
     #object {CurvedCharge rotate <150,0,0> translate <0,-1,-3>}
     #object {StraightCharge rotate <180,0,0> translate <0,0,-2.5>}
     // Charge carriers inside Hall element:
     #if (HallUpwards)
       #object {CurvedCharge rotate <195,0,0> translate <0,-.3,0>}
       #object {CurvedCharge rotate <30,180,0> translate <0,1.15,-1.5>}
       #object {CurvedCharge rotate <0,180,0> translate <0,1.15,1.5>}
     #else
       #object {CurvedCharge rotate <210,0,0> translate <0,-1,-1.5>}
       #object {CurvedCharge rotate <15,180,0> translate <0,.3,0>}
       #object {CurvedCharge rotate <180,0,0> translate <0,-1,1.5>}
     #end
     // Charge carriers on the side facing away from the viewer:
     #object {StraightCharge rotate <180,0,0> translate <0,0,3>}
     #object {CurvedCharge rotate <270,0,0> translate <0,-1,3>}
     #object {StraightCharge rotate <270,0,0> translate <0,-2,4>}
     #object {CurvedCharge rotate <330,0,0> translate <0,-2,3>}
     #object {StraightCharge translate <0,-3,2.3>}
     #if (PlusTowardsViewer)
       scale <1,1,-1>
     #end
     }
       
   #object {PowerSource  // The battery symbolising the power source of the circuit
       #if (PlusTowardsViewer) scale <1,1,-1> #end
       scale 2
       translate <0,-3,0>
       }
   
   #union {    // Pair of magnets
     // The magnet at the left-hand side of the image:
     box {<-15,-1,-1>,<-3,1,1>
       pigment {
         object {
           text {ttf MagnetFont
             #if (NorthAtLeft) "N" #else "S" #end
             ,3,0
             scale 2
             translate <-4.3,-.7,-1.5>
             }
           #if (NorthAtLeft)
             color rgb <1,0,0>
             color rgb .85
           #else
             color rgb .85
             color rgb <1,0,0>
           #end
           }
         }
       finish {ambient .4}
       no_shadow
       no_reflection
       }
     // The magnet at the right-hand side of the image:
     box {<3,-1,-1>,<15,1,1>
       pigment {
         object {
           text {ttf MagnetFont
             #if (NorthAtLeft) "S" #else "N" #end
             ,3,0
             scale 2
             translate <3.2,-.7,-1.5>
             }
           #if (NorthAtLeft)
             color rgb .85
             color rgb <1,0,0>
           #else
             color rgb <1,0,0>
             color rgb .85
           #end
           }
         }
       finish {ambient .4}
       no_shadow
       no_reflection
       }
     }
 
 // 4 x 4 arrows to indicate the direction of the magnetic field:
 #local Ktal=-.75;
 #while (Ktal<1)
   #local Rtal=-.75;
   #while (Rtal<1)
     #object {FieldArrow translate <0,Rtal,Ktal>}
     #local Rtal=Rtal .5;
   #end
   #local Ktal=Ktal .5;
 #end
 
 // Point of view:
 camera {
     location <4,3,-5>
     look_at <.8,-1.3,0>
     }
 
 // Illumination:
 light_source {<20,10,-15> color rgb 1}
 light_source {<-10,20,10> color rgb 1}
 
 // Spotty surroundings outside viewfield to enhance reflective surfaces:
 #declare Spotty=pigment {
   marble
   color_map {
     [0 color rgb 0]
     [1 color rgb .8]
     }
   scale .1
   }
 
 sky_sphere {
   pigment {
     gradient z
     pigment_map {
       [0.00 Spotty]
       [0.88 Spotty]
       [0.88 color rgb 1]
       [1.00 color rgb 1]
       }
     translate -.5
     scale 2
     rotate <35,-32,0>
     }
   }