var r = 16; //1 also

​

function setup() {

  createCanvas(400, 400);

  tree[0] = createVector(width /2, height /2);

}

​

function draw() {

  background(0);

 while(!struck){

  var walker = createVector(random(width), random(height));

  var struck =false;

    for (var i = 0; i < tree.length; i++){

   var d =p5.Vector.dist(walker,tree[i])

  if(d<r*2){

    struck =true;

    break;

  }

      var vel=p5.Vector.random2D();

      walker.add(vel);

    walker.x=constrain(walker.x,0,width);

    walker.y=constrain(walker.y,0,height);

    }

   tree.push(walker);    

  for (var i = 0; i < tree.length; i++) {

    strokeWeight(r);

    stroke(255,100);

    point(tree[i].x, tree[i].y);

  }

 }

}