code: function getRandomPointOnSphere(r) {
    var u = THREE.Math.randFloat(0, 1);
    var v = THREE.Math.randFloat(0, 1);
    var theta = 2 * Math.PI * u;
    var phi = Math.acos(2 * v - 1);
    var x = r * Math.sin(theta) * Math.sin(phi);
    var y = r * Math.cos(theta) * Math.sin(phi);
    var z = r * Math.cos(phi);
    return {
      x,
      y,
      z,
    };
  }
docs: Get a random point on a sphere
  
  @param {Float} r Shpere radius
  @returns {Object} return the point's position