code: function overzoomGeometry(rings, nativeTile, newExtent, newTile) {
    var diffZ = newTile.level - nativeTile.level;
    if (diffZ === 0) {
      return rings;
    } else {
      var newRings = [];
      // (offsetX, offsetY) is the (0,0) of the new tile
      var offsetX = newExtent * (newTile.x - (nativeTile.x << diffZ));
      var offsetY = newExtent * (newTile.y - (nativeTile.y << diffZ));
      for (var i = 0; i < rings.length; i++) {
        var ring = [];
        for (var i2 = 0; i2 < rings[i].length; i2++) {
          ring.push(rings[i][i2].sub(new Point(offsetX, offsetY)));
        }
        newRings.push(ring);
      }
      return newRings;
    }
  }
docs: Use x,y,level vector tile to produce imagery for newX,newY,newLevel