#This script generates a helix double.
#This is intended as the script of a 'Programmable Source'
import math
 
numPts = 80 # Points along each Helix
length = 8.0 # Length of each Helix
rounds = 3.0 # Number of times around
phase_shift = math.pi/1.5 # Phase shift between Helixes
 
#Get a vtk.PolyData object for the output
pdo = self.GetPolyDataOutput()
 
#This will store the points for the Helix
newPts = vtk.vtkPoints()
for i in range(0, numPts):
   #Generate Points for first Helix
   x = i*length/numPts
   y = math.sin(i*rounds*2*math.pi/numPts)
   z = math.cos(i*rounds*2*math.pi/numPts)
   newPts.InsertPoint(i, x,y,z)
 
   #Generate Points for second Helix. Add a phase offset to y and z.
   y = math.sin(i*rounds*2*math.pi/numPts+phase_shift)
   z = math.cos(i*rounds*2*math.pi/numPts+phase_shift)
   #Offset Helix 2 pts by 'numPts' to keep separate from Helix 1 Pts
   newPts.InsertPoint(i+numPts, x,y,z)
 
#Add the points to the vtkPolyData object
pdo.SetPoints(newPts)
 
#Make two vtkPolyLine objects to hold curve construction data
aPolyLine1 = vtk.vtkPolyLine()
aPolyLine2 = vtk.vtkPolyLine()
 
#Indicate the number of points along the line
aPolyLine1.GetPointIds().SetNumberOfIds(numPts)
aPolyLine2.GetPointIds().SetNumberOfIds(numPts)
for i in range(0,numPts):
   #First Helix - use the first set of points
   aPolyLine1.GetPointIds().SetId(i, i)
   #Second Helix - use the second set of points
   #(Offset the point reference by 'numPts').
   aPolyLine2.GetPointIds().SetId(i,i+numPts)
 
#Allocate the number of 'cells' that will be added. 
#Two 'cells' for the Helix curves, and one 'cell'
#for every 3rd point along the Helixes.
links = range(0,numPts,3)
pdo.Allocate(2+len(links), 1)
 
#Add the poly line 'cell' to the vtkPolyData object.
pdo.InsertNextCell(aPolyLine1.GetCellType(), aPolyLine1.GetPointIds())
pdo.InsertNextCell(aPolyLine2.GetCellType(), aPolyLine2.GetPointIds())
 
for i in links:
   #Add a line connecting the two Helixes.
   aLine = vtk.vtkLine()
   aLine.GetPointIds().SetId(0, i)
   aLine.GetPointIds().SetId(1, i+numPts)
   pdo.InsertNextCell(aLine.GetCellType(), aLine.GetPointIds())