• Adobe After Effects Expressions

  Position drives rotation

  Posted by Rich Cho on May 24, 2011 at 4:29 pm

  This seems like a simple thing to do but I just can’t figure it out.
  How do I write an expression that allows an object to rotate based on the position (X and Y) of another object.
  Whenever I try this, it looks like this under rotation:

  thisComp.layer(“Solid 1”).transform.position[0]
  it only rotates when I move “Solid 1” in the X direction.
  When I change it to
  thisComp.layer(“Solid 1”).transform.position[1]
  it only rotates when I move in the Y direction

  I want the layer to rotate when you move “Solid 1” in the X OR the Y direction.

  Hayley Anderson replied 9 years, 8 months ago 4 Members · 3 Replies
• 3 Replies

• 

  Kevin Camp

  May 24, 2011 at 4:48 pm

  you need to use position as a vector (use both x and y). the length() function should do it…

  try using this for the rotation:

  length(thisComp.layer(“Solid 1”).transform.position)

  Kevin Camp
  Senior Designer
  KCPQ, KMYQ & KRCW
• 

  Dan Ebberts

  May 24, 2011 at 4:53 pm

  I think you need a reference point to measure against. There are a couple of ways to do it. One is to just define a static point. This example uses the center of the comp:

  center = [thisComp.width,thisComp.height]/2;
  length(center,thisComp.layer(“Solid 1”).transform.position)

  another way would be to compare the current position to where the layer was at time zero:

  p = thisComp.layer(“Solid 1”).transform.position;
  length(p,p.valueAtTime(0))

  I haven’t tested these, so beware of typos.

  Dan
• 

  Hayley Anderson

  December 23, 2016 at 5:32 pm

  Oh my god, Thank you Dan, I have been trying to find this expression for days!

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