Creating a Horizontally Moving Circle with Random Vertical Motion in BonVision

[chengyuan717]

Hi, I’m a beginner in using BonVision, and I’d greatly appreciate your help. I’m trying to create a visual stimulus where a circular object moves from left to right across the screen. However, I would like the circle to move along a curved path — specifically, I want it to randomly shift up and down in the vertical (y-axis) direction during its horizontal movement. In other words, the object should not follow a straight horizontal line, but a more natural, wavy trajectory.

I’ve gone through the documentation and examples, but I’m not sure how to implement this kind of motion, especially the part where the y-position changes randomly or smoothly over time.

Could you please guide me on how to achieve this in BonVision? If there’s a specific node or script I should look into, I’d be happy to follow up.

Thank you so much for your time and support!
Best,
Yuan

[banchan86]

Hi @chengyuan717 Not sure if this is the best solution, but you can add an ExpressionTransform after RangeAnimation to draw out any curve that can be modelled with a math equation (using functions from the Math class).

For instance something like

will modulate LocationY to give a bounded exponential curve (from -1 to 1) with a sine wave jitter (thanks ChatGPT 😄)
I'm sure there are simpler ones that will give you what you need but I will leave that to you to explore.

You can check out how that is written out in the ExpressionTransform in the attached workflow.
#2241 exponential.zip

[chengyuan717]

Hi @banchan86,

Thank you so much for your help!
I tried the script you shared, and it definitely works. However, when I run it directly, the dot moves upward along the y-axis. So, following your suggestion, I modified the math equation to use A * sin(2πft) instead. This makes the dot move horizontally instead of drifting in one direction along the y-axis.
I have a couple of follow-up questions:
What if I don’t want to use a sine function to define the circular jitter? How could I edit the equation? What about using random numbers ranging from -1 to 1?
I was also wondering—do you know how to control the dot's movement by directly inputting a sequence of x and y values? That might be a more straightforward way to achieve this.

Yuan

[banchan86]

@chengyuan717 Ah I see, I think I got caught up in the "curved path" and thought you wanted an exponential line! So several options:

1. You can continue to use the ExpressionTransform and the Math functions with other equations, check out the links to the documentation in my previous reply to see more examples and a language guide.

2. So if you really just want random Y jitter, then you can do something like this (which I think you tried to do originally) but add an Accumulate operator (so that it updates the position rather than substituting the Y value).

• I'm using a Timer instead of a RangeAnimation here for a slower animation (RangeAnimation is set to the display refresh cycle if I am not mistaken).
• I'm using Zip here also as sort of a substitute for Sample. Sample only works when both sequences are being produced over time. In this case, SampleMany produces the specific number of elements immediately and they are just being queued to be packaged by Zip whenever Timer issues a value.

3. So I don't recommend directly inputting the sequence, but it is possible by creating a CSV file with the values and using CsvReader to read from it. Similar to my previous explanation, all of those elements would be produced immediately, which you can "sample" with Zip and a Timer.

Also updated the attached workflow here.
#2241 random motion.zip

[glopesdev]

@chengyuan717 I want to reiterate everything @banchan86 said above, which should work perfectly. My only observation is that I would probably make sure to use the Timer operator from the Shaders package rather than Reactive.

The reason is that the Timer from Shaders is synchronised with the render loop, so should guarantee frame locked behaviour.

[chengyuan717]

Thank you so much for your help @glopesdev @banchan86 — it was really useful. After running it a few times, I noticed that using random numbers to add jitter on the y-axis can sometimes cause the dots to shift slightly up or down. This makes it hard to ensure that the final dot always lands exactly at (0, 1). I was wondering if it's possible to add some periodicity to the random values, maybe something like a sine function, so that the dot starts from (-1, 0) and ends at (1, 0) in a controlled way. But no worries if that’s too complicated — I think the current setting already meets my immediate needs.

[banchan86]

So instead of really random jitter one way to achieve that is to have pseudorandom jitter - where you define a set of values that add up to 0 and then select randomly from the set (without repetition). If you finish the set, it will return the accumulated value back to 0. Here is one possible way of generating such a set:

Workflow updated:

#2241 random motion.zip