function packID(id){
    var r = id >> 16;
    var g = (id - (r << 8)) >> 8;
    var b = id - (r << 16) - (g<<8);
    return [r, g, b];
}
Pick the object
@param  {number} x Mouse position x
@param  {number} y Mouse position y
@return {clay.Node}