AE ENHANCERS

Posted by Dan Ebberts on AE List June 18 2003

A falling leaf can be a pretty complicated simulation - sometimes they just
fall gently, sometimes they do barrel-rolls, sometimes glide back and forth, or
any combination. These expression roughly simulate the glide back and forth
variation. I tried this on a 3D solid positioned above the camera view,
oriented with Z pointing down and Y pointing in the positive Z direction
(orientation [90,0,0]).

Then I added these three expressions:

POSITION:

yVelocity = 200; //pixels per second
oscFreq = 1.5; //oscillations per second
oscDepth = 35; //oscillation depth (pixels)
drift = 25; // drift (wind?) (pixels per second: - = left, + = right)

value + [oscDepth*Math.sin(oscFreq*Math.PI*2*time) + drift *time,
yVelocity*time,0]

Z ROTATION:

seed_random(index,true);
random(360);

Y ROTATION:

oscFreq = 1.5;
maxTilt = 15; //degrees

maxTilt*Math.cos(oscFreq*Math.PI*2*time)


If you edit the parameters, you need to make sure that the oscillating
frequency is the same in both the position and y-rotation expressions (or map
it to a slider control). If you wanted to apply this to a bunch of leaves,
you'd want to introduce some randomness into the various parameters along with
a random starting phase.