• Adobe After Effects Expressions

  confused about parenting (!) toWorld doesn’t fix things

  Posted by Rob Mcgowan on February 21, 2017 at 9:38 pm

  hi, I have 3 nulls named P1,P2 and P3 evenly distributed on my composition.

  P3 is parented to P2. P2 is parented to P1. P1 has no parent. All the nulls have scale 100%. All have anchorPoint [0,0].

  So I made a fn to calculate distances between them and although the nulls are evenly spaced on screen the two calculated distances are different by a factor of about 7. Using toWorld makes no difference. Changing from position to anchorPoint makes no difference.

  If I move P3 over P2 it’s position in the timeline goes to zero but it’s distance calculated by the fn goes up to about right. If I unparent P2 from P1 this too causes the distance to go up and again looks like it becomes right.

  Can anyone explain how to correctly get the world position of a chain of parented nulls in CS4?

  Thanks

  //this gives wildly wrong results (400 and 73)
D12= getLength(p1.transform.position,toWorld(p2.transform.position));
D23= getLength(toWorld(p2.transform.position),toWorld(p3.transform.position));

  //shouldn't have to do this since P1 is an orphan? and it isn't any better
  D12= getLength(toWorld(p1.transform.position),toWorld(p2.transform.position));

  //this gives zero for the distance
  D23= getLength(toWorld(p2.transform.anchorPoint),toWorld(p3.transform.anchorPoint));

  I've tested this...
function getLength(p1,p2) {
dx=p1[0] - p2[0];
dy=p1[1] - p2[1];
l=Math.sqrt(dx*dx+dy*dy);
return l;
}

  Dan Ebberts replied 9 years, 2 months ago 2 Members · 2 Replies
• 2 Replies

• 

  Rob Mcgowan

  February 21, 2017 at 9:56 pm

  OK, so I read Dan Ebberts cool steam engine page and I think I figured this out.

  I need the distance from P2 to p3 but P2 is parented to P2 so it’s in P2 coordinate space. SOOO the correct distance is just length([0,0] , P3.transform.position). Looks good so far…
• 

  Dan Ebberts

  February 21, 2017 at 10:39 pm

  This should work without regard to parenting:

  p1 = thisComp.layer(“P1”);
  p2 = thisComp.layer(“P2”);
  p3 = thisComp.layer(“P3”);
  d12 = length(p1.toWorld(p1.anchorPoint),p2.toWorld(p2.anchorPoint));
  d23 = length(p2.toWorld(p2.anchorPoint),p3.toWorld(p3.anchorPoint));

  Dan

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