1. A method performed under control of a gesture-based game system, comprising: determining whether an obstacle exists within a playing space associated with a game being currently played on the gesture-based game system; generating in a display area associated with the game a barrier image associated with the obstacle; determining a location of a player and a location of the obstacle in the playing space; determining a distance between the player and the obstacle based at least in part on the determined location of the player and the determined location of the obstacle; generating in the display area an avatar image associated with the player; determining a virtual distance between the avatar image and the barrier image based at least in part on the determined distance between the player and the obstacle; and comparing the determined virtual distance with a predetermined distance limit, wherein the generating the barrier image includes locating the barrier image separated by the determined virtual distance from the avatar image and is performed when the determined virtual distance is shorter than the predetermined distance limit.