• Adobe After Effects Expressions

  Converting one layer’s rotation to another’s Y value

  Posted by Navarro Parker on October 5, 2012 at 5:47 pm

  I’m trying to use a range mapper to convert Layer A’s Z Rotation (0-45°) to Layer B’s Y Position (+/- 100 pixels). Both are 3D layers.

  I think I have the basic concept correct? But I’m getting a class number error in last line of this:

  input = thisComp.layer("Layer A").transform.zRotation;
inputLow = 0;
inputHigh = 45;
outputLow = -100;
outputHigh = 100;
m = linear(input,inputLow,inputHigh,outputLow,outputHigh);
[value[0], value + m[1], value[2]]

  Dan Ebberts replied 13 years, 11 months ago 2 Members · 5 Replies
• 5 Replies

• 

  Dan Ebberts

  October 5, 2012 at 6:07 pm

  I haven’t tried it, but I think you just need to change the last line to this:

  [value[0], value + m, value[2]]

  or this,

  value + [0,m,0]

  Dan
• 

  Navarro Parker

  October 5, 2012 at 6:10 pm

  Your solution works great (of course)!

  Generally speaking, when should I be use (and not use) [0], [1], [2]? I thought 3D position was an array.

  Also, should I be using degreesToRadians?

  In the meantime, I came up with this. But it feels clunky:

  x = thisComp.layer("green").transform.position[0];
y = thisComp.layer("green").transform.position[1];
z = thisComp.layer("green").transform.position[2];

  input = thisComp.layer("solid").transform.rotation;
inputLow = -45;
inputHigh = 45;
outputLow = -100;
outputHigh = 100;
m = linear(input,inputLow,inputHigh,outputLow,outputHigh);
[x, y+m, z]
• 

  Dan Ebberts

  October 5, 2012 at 6:28 pm

  I may have added to your confusion. I got the first option wrong. It should have been:

  [value[0], value[1] + m, value[2]]

  > I thought 3D position was an array.

  It is. But your variable m isn’t, so it doesn’t need array indexing. I like the second option (value + [0,m,0]) where you just let AE do the vector (array) math for you.

  >Also, should I be using degreesToRadians?

  Generally not unless you use one of the JavaScript trig functions.

  Dan
• 

  Navarro Parker

  October 5, 2012 at 6:49 pm

  [value[0], value[1] + m, value[2]]

  value + [0,m,0]

  They both work fine. Is there a reason I should use one over the other?
• 

  Dan Ebberts

  October 5, 2012 at 7:17 pm

  Functionally they’re the same. I like the second one because it’s more efficient (and tidier code, I think). The expression engine knows how to add arrays, so I say take advantage of it. 🙂

  Dan

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