Re: [Visualpython-users] Question: Redrawing vectors

[Bruce S. <bas...@un...>]

 From your description it sounds like you are creating arrows inside your 
main loop. Instead, create the arrows just once, before entering the main 
loop. Then as the magnetic field changes, continually alter the axis 
attributes of the arrows. Here's the basic outline:

Barrow = arrow(pos=(x1,y1,z))
while 1:
     # calculate mag. field B as a vector
     Barrow.axis = scalefactor*B  # alter the axis of the Barrow object

For an example of this, see the VPython demo program toroid_drag.py. If on 
the other hand you create the arrow object inside the loop, each time that 
you create it the old one becomes a (visible) orphan on the screen, and the 
new arrow is displayed. And if you try to make this arrow invisible, the 
old orphaned arrow objects will still be visible, since the name "Barrow" 
has been removed from the old arrows and currently references the most 
recently created object.

If I've misdiagnosed the problem, please show us the relevant portion of 
your program.

Bruce Sherwood

At 12:13 AM 02/06/17 -0400, Karim Diff wrote:
>This question may have been addressed before, but I am
>new to vpython and I have not found the answer so far:
>I am drawing vectors representing the magnetic field surrounding a moving 
>charge but at every iteration my program draws the new vectors on top of 
>the previous ones. I would like to be able to draw only the current 
>vectors. Is there a way of "refreshing" the display as in Java?
>I tried to tinker with the visible attribute of my vectors (trying to turn 
>"visible" on and off) but it did not work.
>Thanks for any pointers.
>
>Karim Diff