Random Grid Movement

Here's an expression from the random motion family that will move objects randomly along a grid to a new position on the grid.

To demonstrate this, I applied this expression to the position property of a square solid and then duplicated the solid a bunch of times.

columns = 10; //number of columns in grid
tHold= .2; //hold time (must be less than tmin)
tMin = .5; //minimum cycle time (can't be zero)
tMax = 1; //maximum cycle time

gap = this_comp.width/columns;
origin = [gap,gap];
xGrid = columns - 1;
yGrid = Math.floor(this_comp.height/gap) - 1;

start = 0;
end = 0;
j = 1;

while (time >= end){
  j += 1;
  seedRandom(j,true);
  start = end;
  end += random(tMin,tMax);
}
targetX = Math.floor(random(0,xGrid)); 
targetY = Math.floor(random(0,yGrid)); 
seedRandom(j-1,true);
x = random(); //this is a throw-away value
oldX = Math.floor(random(0,xGrid)); 
oldY = Math.floor(random(0,yGrid)); 

if(targetX == oldX && targetY == oldY){
  origin + [oldX,oldY]*gap;
}else if (time - start < tHold){
  origin + [oldX,oldY]*gap;
}else{
  deltaX = Math.abs(targetX - oldX);
  deltaY = Math.abs(targetY - oldY);
  xTime = (end - start - tHold)*(deltaX/(deltaX + deltaY));
  yTime = (end - start - tHold)*(deltaY/(deltaX + deltaY));
  if (time < start + tHold + xTime){
    startPos = origin + [oldX,oldY]*gap;
    targetPos = origin + [targetX,oldY]*gap;
    easeOut((time - start - tHold)/xTime, startPos, targetPos);
  }else{
    startPos = origin + [targetX,oldY]*gap;
    targetPos = origin + [targetX,targetY]*gap
    easeIn((time - start - tHold - xTime)/yTime, startPos, targetPos);
  }
}

Note that the number of rows is calculated from the number of columns and that the objects come to rest at the intersection of rows and columns.

Adjust the number of columns, hold time, minimum and maximum cycle time to suit your needs.

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