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Difficulty animating a line along motion path

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Gabriel Curtin
Difficulty animating a line along motion path
on Jan 16, 2020 at 12:02:55 pm

Basically what I'm trying to do is animate a green line to follow the finger of a figure I have filmed as though they are drawing the line.
I want the line to stay on the screen once they have drawn it.
The video will loop so the figure will perform the same gesture over and over again. With each loop I want the line to get thicker until, eventually, the whole screen is blotted out. At the beginning of each loop all the previous lines that were drawn are to remain on the screen.
I've attached a few mockup images of how I picture it as well as my attempt at animating it.

Here is the link to my attempt: https://vimeo.com/363282745
and here is the password to view the video: gabrielpoint

The animation attempt is only of the first loop and the only tutorial I could find made the line using some sort of bubbly animation where all the bubbles are very densely packed and so appear like a solid line. However, as soon as you increase the size of the line it is very apparent it is made of bubbles! I'm thinking there should be an easier way... Also you'll notice I've motion tracked the figure's movements but they've been nudged a bit out of place. I can fix that up later I'm mainly hoping to get advice on animating the line. If anyone has any ideas I'd love to hear them!

Let me know clarification is needed, I realise it's a little confusing.

Also I should note I'm an after effects novice

Many thanks

Gabriel

Here is a still mockup of how I picture the video unfolding:


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Graham Quince
Re: Difficulty animating a line along motion path
on Jan 19, 2020 at 2:59:06 pm

There’s a few steps needed but it’s all possible.

1) Create an null object and either track or manually keyframe it to follow the guys finger.

2) Then link this Null to CC Particle world using a set of expressions, Ive shared a tutorial on how to do that:





3) In the Physics section of CC Particle World, set the velocity and gravity to 0

4) In the Particle section, use the birth and death sizes they have the particles start small and grow big.

http://www.YouTube.com/ShiveringCactus - Free FX for amateur films
http://shiveringcactus.wordpress.com/ - FX blog


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Gabriel Curtin
Re: Difficulty animating a line along motion path
on Jan 20, 2020 at 10:08:48 pm

Hi Graham,

Thanks for the detailed instructions. I'm pretty sure that this is the method I used to animate the line in the sample video I linked in the original post. The problem being is that when I increase the particle sizes to make the line bigger it becomes obvious that the line is made up of particles rather than being a single, solid line.

I'll have another go and follow your instructions and let you know if the same thing happens or not.

Thanks,

Gabriel


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Tomas Bumbulevičius
Re: Difficulty animating a line along motion path
on Jan 20, 2020 at 7:53:35 am

Hey Gabriel, few questions:

1. How do you 'draw' the lines initially? Is it based on motion tracker data?
2. How do you animate the lines? Is it done manually?

Based on answer above, I might have a different solution than Graham has suggested, based on shape paths instead (you could control the stroke width to achieve 'filling effect').

Find out more:
After Effects Tutorials: motion design, expressions, scripting.
Boxer - Dynamic Text Boxes Template with a Live Preview


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Gabriel Curtin
Re: Difficulty animating a line along motion path
on Jan 20, 2020 at 10:14:39 pm

Hi Tomas,

Yeah its a null object that follows the path set by the motion tracker. The line is animated by linking it to CC particle.
As described in the original post though, this means that when I increase the size of the particles to make the line bigger, it becomes clear it isn't a solid line.

If you have another suggestion I'd love to try it.

I should note I'm happy to start from scratch.

Thanks,

Gabe


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Tomas Bumbulevičius
Re: Difficulty animating a line along motion path
on Jan 21, 2020 at 10:49:17 am

Hey Gabe, thanks for a clarification.

While I am not certain whether animation itself was made dynamically or manually with CC Particles, here is my take on this, to achieve it through shape layer instead.

1. Selection tracking data of position.
2. Copy it.
3. Create a shape layer.
4. Apply a single path to it with a pen tool.
5. Select path in layer stack and paste position data.
6. What you will get, is a path that matches position (might need to tweak its origin of placement)

From this point, you could apply Trim paths and animate the line as it goes (yeah, manual stuff out there). BUT if you are going to do this in a loop, then it would be a matter of duplicating the line and increasing the stroke width.

Is this is something that might work for your case, or not at all?

Find out more:
After Effects Tutorials: motion design, expressions, scripting.
Boxer - Dynamic Text Boxes Template with a Live Preview


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Gabriel Curtin
Re: Difficulty animating a line along motion path
on Jan 27, 2020 at 2:29:50 am

Thanks for getting back to me with this suggestion.
I ended up making it work with the Write-On effect.

I very much appreciate your help!


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Cassius Marques
Re: Difficulty animating a line along motion path
on Jan 21, 2020 at 12:56:26 pm

Is your hand tracked to 3d? or you just have 2d position?

If its 3d you must use a particle generator, just increase the number of particles.

If its 2d, there is an effect called Write-on.

Cassius Marques
http://www.zapfilmes.com


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Gabriel Curtin
Re: Difficulty animating a line along motion path
on Jan 27, 2020 at 2:28:57 am

Hi Cassius,

Thanks so much the Write-on effect worked!

My only issue now is that I need the px size to be larger than 200, it seems to cap it at that size.
I'm sure I can figure that out though.

Thanks for the suggestion, much appreciated.

Gabriel


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