I’m trying to make an animation by growing a curve. I have a python script like this, which is based on http://blenderscripting.blogspot.fr/2011/05/blender-25-python-bezier-from-list-of.html

import bpy
from mathutils import Vector

w = 1 # weight
Scale = 0.03

def readCoords(filename):
    with open(filename, 'r') as File:
        Coords = [[float(x) * Scale for x in line.split()] for line in File]
        return list(map(Vector, Coords))

ListOfVectors = readCoords("/Volumes/Stuff/3d/Lorenz/3d-data.txt")

def makePolyLine(objname, curvename, cList):
    curvedata = bpy.data.curves.new(name=curvename, type='CURVE')
    curvedata.dimensions = '3D'

    objectdata = bpy.data.objects.new(objname, curvedata)
    objectdata.location = (0,0,0) #object origin

    polyline = curvedata.splines.new('NURBS')

    for i in range(len(cList)):
        # bpy.context.scene.frame_set(i+1)
        if i > 0:
        x, y, z = cList[i]
        polyline.points[i].co = (x, y, z, w)

makePolyLine("NameOfMyCurveObject", "NameOfMyCurve", ListOfVectors)

Basically I read the coordinates of points from a file, and add them to a curve in sequence. My question is, how can I animate this process (eg. add 1 point per frame)? I notice there’s a build modifier, but I want precise control on this, so that I know the exact coordinate of the end of the curve at each frame.

  • $\begingroup$ I'm not sure you can animate adding points but you could create a curve with len(cList) points all at the same location then animate moving them into place. You would have to create a hook for each point and keyframe the movement of each hook. see wiki page on hooks $\endgroup$
    – sambler
    Dec 31, 2013 at 6:38
  • $\begingroup$ This might give some some pointers youtube.com/watch?v=CkbC787SvGk $\endgroup$
    – stacker
    Dec 31, 2013 at 15:34
  • $\begingroup$ @sambler Thanks for the reply. I’m not sure if it’s useful, but I’ll think about it. $\endgroup$
    – MetroWind
    Jan 8, 2014 at 3:37
  • $\begingroup$ @stacker It looks interesting. The problem is though the same with using a build mod. I don’t have precise control, i.e. I don’t know how the movement of the control object is mapped to the curve length. But thanks for the link~ $\endgroup$
    – MetroWind
    Jan 8, 2014 at 3:39

1 Answer 1


I had this exact same problem a couple of months ago. The solution irc provided to me was to create a full curve and animate the End Bevel Factor. End Bevel Factor on the properties of the curve data

The beginning of your curve is bevel_factor=0. The end of your curve is 1.0. I am pretty sure it maps from the bevel factor to the index of a control point. So if your curve has 11 points (0..10), then bevel 0.3 will include control points (0..3) .

Consider carefully if you want to animate it with a linear animation curve or the default bezier curve.

  • 1
    $\begingroup$ Is there any function that allows me to calculate the end point of the bevel from this “end bevel factor”? Because I really need that… $\endgroup$
    – MetroWind
    Feb 5, 2014 at 23:04
  • $\begingroup$ Wonderful, Never thought to use it because of "Bevel" kinda ambigus $\endgroup$
    – snoob dogg
    Sep 18, 2018 at 22:34

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