• Adobe After Effects

  Make Opacity 0 In Negative Z Space

  Posted by Guiboche on May 15, 2006 at 12:39 am

  Hello,

  I was just wonder, how might you use an expression to control a layer’s opacity when it moves beyound 0 in the 3D world.

  I understand that 0,0,0 = X,Y,Z

  When a layer moves into negative values into Z based on it’s world position, not by actually moving it, I want the opacity to = 0.

  Example, I have a layer attached to a null, and the null is rotating on the Y. When the layer connected to the null moves into negative world space on the Z, I want it’s opacity to = 0.

  Below is what I want to do:
  

  In the above example, opacity is dipping down when the layer moves into negative Z space. How might I do this with expressions?

  Thanks a lot 🙂

  Guiboche

  Guiboche replied 20 years, 4 months ago 8,539 Members · 1 Reply
• 1 Reply

• 

  Guiboche

  May 15, 2006 at 3:31 am

  Well, no one replied yet, but I figured it out 🙂

  The expression is

  a = toWorldVec([0,0,1]);
  b = position – toWorld(anchorPoint);
  c = dot(a,b)/length(b);
  if (c > 0) 0 else value

  You change the 0,0,1 to 0,0,-1 for in front or behind.

  Later

  Guiboche

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