• Adobe After Effects Expressions

  Ensuring two ‘random’ expressions do not produce same value

  Posted by Marcus Round on January 14, 2015 at 11:01 am

  I have a Beam that I want to go from one randomly selected Blob to another.

  So I select a random Blob for the “Start Point” of the Beam:

  blobs = thisComp.layer("2").content("Blobs");
numBlobs = blobs.numProperties;
myBlob = Math.ceil(random(numBlobs));

  anchorPoint+blobs.content(myBlob).transform.position;

  So far, so good. Plug the same expression into the “End Point” of the beam, and there’s a chance that the Beam will pick the same Blob as both its start and end point, which we don’t want.

  I thought I’d be clever and put this into the “End Point”:

  blobs = thisComp.layer("2").content("Blobs");
numBlobs = blobs.numProperties;
myBlob = Math.ceil(random(numBlobs));

  start = thisLayer("Effects")("Beam")("Starting Point");
do{
end = anchorPoint+blobs.content(myBlob).transform.position;
}while(start == end);
end

  But this doesn’t seem to have any effect. Any ideas?

  Dan Ebberts

  

  replied 11 years, 3 months ago 2 Members · 3 Replies
• 3 Replies

• 

  Dan Ebberts

  January 14, 2015 at 5:57 pm

  I think I would add a point control to the layer with the Beam effect so that you can do the calculation for both points all in one place, with something like this (not tested(:

  blobs = thisComp.layer(“2”).content(“Blobs”);
  numBlobs = blobs.numProperties;
  blob1 = Math.floor(random(numBlobs));
  blob2 = (blob1 + Math.floor(random(numBlobs-1)))%numBlobs;
  [blob1+1,blob2+1]

  Then your starting point and ending point expressions would look like this:

  Math.round(effect(“Point Control”)(“Point”)[0])

  and

  Math.round(effect(“Point Control”)(“Point”)[1])

  Dan
• 

  Marcus Round

  January 15, 2015 at 3:30 pm

  Thanks Dan,

  But I’m not sure I was clear. If I’m reading your code correctly, each expression will output a single number (either the x or y co-ordinate of a point), but I am looking to pick two different points.

  After tinkering around, from what I can find the problem with my original code is perhaps to do with the use of arrays in conditional statements.
  I tried paring it down to its simplest essence: I made a text layer, and added a point control to the text layer. In the source text, I put this code:

  if(effect("Point Control")("Point")==[600,600]){"true"}else{"false"}

  Which seems fairly straight-forward, but the point control is set to 600,600 and it still evaluates to “false”. Am I doing something wrong?

  In my original code, I am checking if “start” and “end” are equal, and both are arrays.
• 

  Dan Ebberts

  January 15, 2015 at 4:59 pm

  I’m sorry, I botched the expressions for the starting and ending point expressions. What you get from the expression in the point control is two blob numbers, one for start one for end. So your starting and ending point expressions should pick those up, but then use them as you used myBlob in your original expression.

  Dan

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