code: function(shape){
          if(shape.parent){
              throw new Error("It is not possible that you add to the multi-rigid body the shape of one");
          }
          if(this.shapes!=null)(this.shapes.prev=shape).next=this.shapes;
          this.shapes=shape;
          shape.parent=this;
          if(this.parent)this.parent.addShape(shape);
          this.numShapes++;
      }
docs: I'll add a shape to rigid body.
  If you add a shape, please call the setupMass method to step up to the start of the next.
  @param   shape shape to Add