_sphere = function(){
      var u,v,p;
      for (var i = 0; i <= this.detailY; i++){
        v = i / this.detailY;
        for (var j = 0; j <= this.detailX; j++){
          u = j / this.detailX;
          var theta = 2 * Math.PI * u;
          var phi = Math.PI * v - Math.PI / 2;
          p = new p5.Vector(radius * Math.cos(phi) * Math.sin(theta),
            radius * Math.sin(phi),
            radius * Math.cos(phi) * Math.cos(theta));
          this.vertices.push(p);
          this.uvs.push([u,v]);
        }
      }
    }
@private
helper function for creating both cones and cyllinders