Creating Polyline Animation in Bongo


I am in Bongo and trying to find a way to animate the creation of a polyline. I want to be able to start from a specific tick, start a polyline, move to a different tick, and continue drawing the polyline. In my case, it should animate in the direction I am drawing in, which is linear.

An alternative I tried was to use the Scale-1D command by drawing the line, changing the pivot to the end, and then scaling it. However, this is a very tedious process in which drawing the polyline would make it much simpler to get faster results. Let me know if anyone has a solution.

Hi DRGR, welcome to our community.

DRGR.3dm (58.5 KB)

A way is to use Sweep 1 rail with History Recorded. It draws a ribbon which is viewed as a line in Top View.

A short vertical line (“tractor”) is moved along the path by means of a Simple Constraint ‘To Path’. The curve used as a path for the Simple Constraint as well as the rail for the Sweep 1 is located on layer 01 which is hidden.

A second short vertical line is stable at the start of the path.

The Sweep 1 uses the (hidden) path for ‘rail’ and both short lines for ‘sweep shapes’. It is necessary to position the timeline slider away from 0 to be able to make the sweep. Obviously Record History must be enabled in order to make the Sweep dynamic.

History based animations cannot be pre-viewed by clicking the Play button. You have to press and hold the next tick button of the timeline-slider.

I hope this solution matches your intention,

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There is a video on the use of History in Animation on my YouTube channel.

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Hello Luc,

I appreciate your help!

I did have an additional question. In your YouTube video, you used Sweep 1 to loft two shapes together. I am doing the same thing with your solution for two circles to make them look like cables. Is it possible to do this with just polylines, or does it have to be an extruded object for it to work?

Edit: I am struggling with Sweep 1 not following the entire length. I have simplified the cables, but this motion would happen 24 times. I have it for 200 frames. At frame 49, it works until it hits frame 50 and stops. On the frame it is supposed to turn, it says, “History failed to update 1 object”.


Indeed you will get a kind of cable when you use 2 small circles instead of the 2 small vertical lines in my example above. In order to get the shape right a “Look Along Z Up” constraint is needed instead of a “To Path” constraint. A Look Along constraint will keep de tractor circle perpendicular to the path.

You can find some more info on the Simple Constraints on Rhino - Object Properties

About your last question: Maybe your issue is due to the Tweenings default setting being “Cardinal Spline”. Changing the Tweening of keyframe 100 to ‘Linear’ might help out - give it a try.
More info on Rhino - Tweening

Although … your screenshot 2 is puzzling me. When you post or mail me the model I can have a closer look. :face_with_monocle:


Hello Luc,

I emailed you the model as I tried your suggestion and was still having the same issue.

HI Dante Rafael,

One way or another it has to do with the algorithm of Sweep 1 Rail in combination with History.
Changing the degree of the “Cable Path” curve to 2 (use the ChangeDegree command) fixes the issue in your model. The curve is somewhat smoothed, but I guess that doesn’t harm (on the contrary).


BTW I guess you’ll have to adapt the shape of the Rings anyway – modify the design of the notch to accommodate the cross-section of the cable.

Hello Luc,

Thank you for the response. I wanted to let you know I had to delete two odd points in my polyline for what you recommended to work. Later this week, I will work on the full-length cable system, which would need to loop around 24 times. If I run into any other issues, I will let you know.

I don’t know exactly what you mean by “odd points”, but I’m glad the degree trick worked for you.
Assuming the full system will use 1 long cable let’s hope the History can cope with the complexity of the path. Please keep us posted.