From: "Chris Zwar" <chris@chriszwar.com>
To: "After Effects Mail List" <AE-List@media-motion.tv>
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Message-ID: <W4428913914247361392944393@atl4webmail19>
Date: Fri, 21 Feb 2014 00:59:53 +0000
Subject: Re: [AE] 3D ribbon with Particular
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Forget the obscuration layer, you need to create and use a Z depth map.  =
I do this a fair bit with particular within AE.

There are 2 ways - you can buy a plugin (which is accurate but very slow)=
 or you can use an expression, which is fast and free but a bit of a pain=
 and not always 100% perfect (because the corners of a layer are a differ=
ent distance to camera than the centre).

To do it in AE, you need to duplicate your main composition with all your=
 3D layers and make a Z-depth version.  Strip out everything that isn't a=
 3D layer and isn't going to interact with the ribbon.  Add the fill effe=
ct to each layer, apply an expression to the colour to fill it with a sha=
de of grey based on the distance to the camera:


camp=3DthisComp.layer("Camera 1").toWorld([0,0,0]); // camera position //=

lp=3DthisLayer.toWorld(thisLayer.anchorPoint); // layer position //
d=3Dlength(camp,lp); // distance from camera to layer //

min=3D0; // this this number for white in particular //
max=3D20000; // use this number for black in particular //

v=3Dlinear(d,min,max,1,0); // convert distance to value 0 - 1 //

[v,v,v,1]


To keep things speedy I would pre-render the z depth map, import it and u=
se it with particular -use the same camera distance value in particular a=
s the min and max values in the expression.


-Chris
-----Original Message-----
From: Teddy Gage [mailto:teddygage@gmail.com]
Sent: Friday, February 21, 2014 10:58 AM
To: 'After Effects Mail List'
Subject: [AE] 3D ribbon with Particular

     So I am working for a fashion brand asking for a 3D ribbon effect th=
at
twists through fields of photos and video, going in front of and behind t=
he
images. My first thought was 3D stroke, but it didn't work, as I need it =
to
have some shading from the comp lights. There's also the issue of painful=
ly
retiming the stroke moves using percentages of completion, and not actual=
ly
having full "3D" control. (I can't draw a path that goes in all dimension=
s,
just postcard transforms on the 2D mask paths, AFAIK.) I may however use =
it
for some simple bending and repeating elements.

     My next idea is to use a particular 2.0 layer with 0 emit velocity,
and having the emitter tied to a null that I can then fully animate throu=
gh
3D space. So far this is working pretty well. Comp lights work, it is eas=
y
to control.  However I am having some of the classic issues with Particul=
ar
where it crosses other 3D objects in the scene and doesn't respect the
stacking order. The ribbon is either completely in front of or completely=

behind the images.

- now I could add 1 or 2 "obscuration layers" but it is not reasonable to=

do this for over a hundred layers individually

- Would I need to precomp the entire layout, collapse transformations, an=
d
THEN use the precomp as an obscuring layer? Is this even possible? It wou=
ld
be a difficult way to work, I'd need to have every element layed out in 3=
D
first. Doable, but I'd prefer to create both at once.

- is there another solution I'm not thinking of? A good script for
Particular maybe?

Thanks,
-TG


-- 
_____________________________
VFX & Motion Graphic Artist
teddygage dot com