How to define a single scalar as an input parameter for Programmable Filter

I would like to create a custom filter consisting of the programmable filter and others. The programmable filter has a hardcoded parameter in it, that I would like to define as an input parameter. Is that possible?

As an example, let’s take the helix code from the tutorials (below). Is it possible to have length be an input field for the filter instead of it being hardcoded?

#This script generates a helix curve.
#This is intended as the script of a 'Programmable Source'
import math

numPts = 80 # Points along Helix
length = 8.0 # Length of Helix
rounds = 3.0 # Number of times around

#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 the Points along the Helix
   x = i*length/numPts
   y = math.sin(i*rounds*2*math.pi/numPts)
   z = math.cos(i*rounds*2*math.pi/numPts)
   #Insert the Points into the vtkPoints object
   #The first parameter indicates the reference.
   #value for the point. Here we add them sequentially.
   #Note that the first point is at index 0 (not 1).
   newPts.InsertPoint(i, x,y,z)

#Add the points to the vtkPolyData object
#Right now the points are not associated with a line - 
#it is just a set of unconnected points. We need to
#create a 'cell' object that ties points together
#to make a curve (in this case). This is done below.
#A 'cell' is just an object that tells how points are
#connected to make a 1D, 2D, or 3D object.

#Make a vtkPolyLine which holds the info necessary
#to create a curve composed of line segments. This
#really just hold constructor data that will be passed
#to vtkPolyData to add a new line.
aPolyLine = vtk.vtkPolyLine()

#Indicate the number of points along the line
for i in range(0,numPts):
   #Add the points to the line. The first value indicates
   #the order of the point on the line. The second value
   #is a reference to a point in a vtkPoints object. Depends
   #on the order that Points were added to vtkPoints object.
   #Note that this will not be associated with actual points
   #until it is added to a vtkPolyData object which holds a
   #vtkPoints object.
   aPolyLine.GetPointIds().SetId(i, i)

#Allocate the number of 'cells' that will be added. We are just
#adding one vtkPolyLine 'cell' to the vtkPolyData object.
pdo.Allocate(1, 1)

#Add the poly line 'cell' to the vtkPolyData object.
pdo.InsertNextCell(aPolyLine.GetCellType(), aPolyLine.GetPointIds())

#The Helix is ready to plot! Click 'Apply'.

Yes, it is possible. But you’ll have to write your slightly differently using the PythonAlgorithm. This will allow you to add parameters and gui interface to your algorithm.


section 4.4 Python Algorithm.