code: function(p) {
          currentBB = sim.getBoundingBox();
  
          var size = currentBB.topright.subtract(currentBB.bottomleft);
          var sx = p.subtract(currentBB.bottomleft).divide(size.x).x * bb.w + bb.x1;
          var sy = p.subtract(currentBB.bottomleft).divide(size.y).y * bb.h + bb.x1;
  
          return new Springy.Vector(sx, sy);
        }
docs: var targetBB = {bottomleft: new Springy.Vector(-2, -2), topright: new Springy.Vector(2, 2)}; convert to/from screen coordinates