1. A computing system, comprising: a peripheral input configured to receive depth images from a depth camera; a display output configured to output a user interface to a display device, the user interface including a button; a logic subsystem operatively connectable to the depth camera via the peripheral input and to the display device via the display output; and a data holding subsystem holding instructions executable by the logic subsystem to: receive from the depth camera one or more depth images of a world space scene including a human target; translate a world space position of a hand of the human target to a screen space cursor position of the user interface such that movement of the hand in world space causes corresponding movement of a cursor in screen space; and when the cursor overlaps the button in the user interface, actuate the button responsive to a movement of the hand in world space that changes the cursor position by a depth threshold along a z-axis regardless of an initial z-axis position of the cursor.