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# After Effects Expressions

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## Interpolating between Shape/Mask Paths

### Feb 22, 2012 7:03 PM

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Hi,

At 1:48 in this video, http://vimeo.com/36068222, this animator has the character's face moving horizontally by animating a mask. Looks pretty easy to do.

What I'm wondering, is whether it's possible to have a character animated in this style move their head both horizontally and vertically at the same time. So, that would be two expressions sliders (vertical position and horizontal position) and 6-9 base shapes (up and center, center and center, down and center, up and turned, center and turned, down and turned, and maybe a few pictures in between). But to do that, After Effects would need to be able to interpolate between multiple mask/shape paths at once.

I doubt that AE has this feature built into it (though if it did, that'd be awesome), so I'm wondering if that can be done with expressions. For example, I know it's possible to write an expression that will interpolate a layer's position with the following code:

val1 = transform.position.key(1);

val2 = transform.position.key(2);

val3 = transform.position.key(3);

mX = val1[0] + (val2[0] - val1[0])*effect("Left-Right")("Slider") + (val3[0] - val1[0])*effect("Down-Up")("Slider");

mY = val1[1] + (val2[1] - val1[1])*effect("Left-Right")("Slider") + (val3[1] - val1[1])*effect("Down-Up")("Slider");

[mX, mY];

But can a similar approach be taken to mix together paths? Thanks,

--Saib

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