1. A method of interfacing with a machine, comprising: generating position data describing a respective current position of each of one or more game objects in relation to a playing surface defining a boundary of a field of play of a game involving use of the one or more game objects in the field of play; displaying on the playing surface a graphical interface image, wherein the graphical interface image demarcates a visible interface zone on the playing surface; determining whether the position data in relation to the displayed graphical interface image satisfies an input instruction predicate for an input instruction, wherein the determining comprises determining whether at least one of the game objects is present in the interface zone and the input instruction predicate comprises a requirement that the one or more game objects be present in the interface zone for at least a prescribed period of time; and in response to a determination that the position data satisfies the input instruction predicate, executing the input instruction on the machine.