problems with circular extrusion

[Falky]

hello everyone, i am just experimented a bit with vpython and extrusions. i wanted to create an extrusion out of 5 segments in a shape of a circle. i also wanted it to be a bit radom everytime. Now it works but sometimes it is not a circle but an elipse. maybe someone can tell me what i am doing wrong. 

My Code:

import vpython as vp

import random as rd

i = 0

t = 5

pathv1 = vp.vec(rd.uniform(-t,t),rd.uniform(-t,t),i)

print(pathv1)

i = i+2

pathv2 = vp.vec(rd.uniform(-t,t),rd.uniform(-t,t),i)

print(pathv2)

i = i+2

pathv3 = vp.vec(rd.uniform(-t,t),rd.uniform(-t,t),i)

print(pathv3)

i = i+2

pathv4 = vp.vec(rd.uniform(-t,t),rd.uniform(-t,t),i)

print(pathv4)

i = i+2

pathv5 = vp.vec(rd.uniform(-t,t),rd.uniform(-t,t),i)

print(pathv5)

i = i+2

pathv6 = vp.vec(rd.uniform(-t,t),rd.uniform(-t,t),i)

print(pathv6)

myshape = vp.shapes.circle()

mypath = [ pathv1,pathv2,pathv3,pathv4,pathv5,pathv6]

paperclip = vp.extrusion(shape = myshape, path = mypath, color=vp.color.yellow)

while True: vp.rate(30)

[John]

Maybe you can have a look at the vpython extrusions demo program for clues of what you might be doing wrong.

https://glowscript.org/#/user/GlowScriptDemos/folder/Examples/program/Extrusions

To see the source code for these extrusion shapes in the demo just click onView this program link.

John

[Bruce Sherwood]

John, there really is something wrong with the extrusion object. I have no idea why the circle shape is sometimes rendered as an ellipse; I've never seen this effect before. The bug is seen in both the vpython module and in Web VPython.

Bruce

[Falky]

it seems to depend on the first to vectors but i cannot confirm it 100%

[Bruce Sherwood]

Here is a minimal program that shows that the error does indeed occur when the first step in the path has both nonzero y and nonzero z components: 

from vpython import *
myshape = shapes.circle()
mypath = [vec(0,0,0), vec(0,-5,-2)]
extrusion(shape=myshape, path=mypath)

So it's definitely a bug in the extrusion object. The only way around this at the moment would seem to be to build the extrusion with a different orientation, then rotate it to the desired orientation.

Many thanks for reporting this problem!

Bruce