Link cc particle world producer to an emitter in after effects

[Michael Lansdell]

I tried this:

But then all trace of the particles disappear!
Is that what you meant? I got those expressions by alt clicking on the particle producer positions and then pick-whipping to the corresponding position of the light I want to follow the path of. I should probably point out I’ve tried this without the wiggle expression on the light too, as I wondered if that was the problem, but it didn’t make a difference.

Thank you!

[Michael Lansdell]

This project was meant to be a fool around and see what happens kind of thing, but I’m just getting frustrated now. Whilst those expressions are on I can’t seem to get anything visual produced by Particle World. It’s all very upsetting!

I’ve included a couple of screen shots here, one is without the expressions to illustrate what I want the particles to look like across the path:

And this is with the expressions on, and the birth rate RIGHT up:

I’m still fiddling with all this, but if you (or anyone!) have a brainwave I’d be keen to hear it :o)

Many thanks, again!

Michael Lansdell

Online/Offline Editor

My system:

2 x 3 GHz Quad-Core Intel Xeon
5GB DDR2 RAM
512MB ATI Radeon X1900 XT
OS X 10.4.11
Final Cut Pro 6.0.4
After Effects CS4
Blackmagic Design DeckLink HD Extreme (6.6.2)

Take a gander at my personal blog:

http://www.monstersareart.co.uk

[Kevin Camp]

cc particle world uses coordinate values based on a ratio of the position to the comp’s width, rather than pixels, so it’s a little goofy to set it up.

andrew has a tutorial that covers that, it’s the one that creates a 3d stroke effect using particle world. you might want to check that one out.

basically you need to add this width ratio into your expressions. so you expressions would look something like this…

position x:
target = thisComp.layer(“Null 1”); // this would be your layer to track
(target.position[0]-(thisComp.width/2))/thisComp.width

position y:
target = thisComp.layer(“Null 1”); // this would be your layer to track
(target.position[1]-(thisComp.height/2))/thisComp.width

position z:
target = thisComp.layer(“Null 1”); // this would be your layer to track
target.position[2]/thisComp.width

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW

[Michael Szalapski]

Where is the camera pointing?

– The Great Szalam
(The ‘Great’ stands for ‘Not So Great, in fact, Extremely Humble’)

No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.

[Kevin Camp]

i just took a closer look, and it’s a ratio of the position to the layer’s width… which is often the same as the comp, but the expressions are more correct like this…

position x:
target = thisComp.layer(“Null 1”); // this would be your layer to track
(target.position[0]-(thisComp.width/2))/width

position y:
target = thisComp.layer(“Null 1”); // this would be your layer to track
(target.position[1]-(thisComp.height/2))/width

position z:
target = thisComp.layer(“Null 1”); // this would be your layer to track
target.position[2]/width

also note that pixel aspect ration of both the comp and layer are not accounted for, so to get the most precise track you should be working with a square pixel comp and layer… or add par corrections to the expressions.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW

[Michael Lansdell]

You’re amazing! Thank you! I don’t entirely understand the expression, but I think I’ll be able to work backwards from it to get there. I think part of the problem was that I was using a 16:9 comp with Pal anamorphic dimensions, meaning that even when I could things linked they were offset quite a bit. But that aside, I was miles away from doing this. Hopefully I’ll be able to make something fun using this.

Many thanks!

[Kevin Camp]

[Michael Lansdell] “I don’t entirely understand the expression”

the scripting makes the math look harder than it really is…

the first part of each expression isn’t entirely necessary, but it makes it a lot easier to point the expression at a given layer. it just creates a variable name ‘target’ and is designed to allow you to use the expression pickwhip to quickly select the layer that you want to pull values from.

the math comes after that. in the case of x and y positions, the layer that you want to pull values from is in ae’s comp space, which is zeroed in the upper left corner of the screen. particle world is zeroed in the center of the layer, so the expression needs to account for that first.

all (target.position[0]-(thisComp.width/2)) is doing is subtracting half the comp’s width (or height) from the corresponding position value of the target layer will zero it’s position in the center of the comp. note, that isn’t necessary for the z position.

then you just need that zeroed value expressed in a ratio to the layers width by dividing it by the particle world layer’s width attribute.

easy 😉

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW

[Rob Mize]

Kevin…

Terrific solution… I knew the answer had to be in expressions, but I have a lot more to learn in that area before I can solve such a problem.

Thanks very much for posting.

Regards…

Rob Mize