Attaching trails or arrows

[Bruce Sherwood]

There is now improved documentation on attaching trails or arrows to moving objects:

http://www.glowscript.org/docs/VPythonDocs/trail.html

[moca...@gmail.com]

Dear Bruce

I have tried the command attach_arrow under a Jupyter notebook in my Debian system and it does nothing: no trail shows up for a moving ball :-( Does it only work under Glowscript?

Best

[Bruce Sherwood]

Thanks for your report. Consider the following program:

b = box()

attach_arrow(b, "axis", scale=3,

         shaftwidth=0.3, color=color.green)

b.pos = vec(1,0,0)

print(b.axis)

scene.pause()

b.axis = vec(1,1,0)

print(b.axis)

I find that this works properly in GlowScript. In Jupyter and IDLE VPython 7 displays the arrow but in the direction of "up" instead of the specified "axis"! Very strange. And it always displays the direction of "up" no matter what object vector I name. So there is a serious bug in VPython 7.

You say that there is no trail, but there shouldn't be a trail if you specify attach_arrow. Instead, there should be an arrow attached to the moving object.