The exemplary illustrative non-limiting technology herein enables 3D viewing on conventional 2D displays such as home television sets by tracking a person's viewpoint. Detecting a player's viewpoint movement to change the viewing of the displayed object gives the illusion that the object is physically present in three-dimensional space. Viewpoint movement detection can provide collision-related game logic benefits such as allowing a player to dodge projectiles, giving a game character an ability to “see” the player when not behind line-of-sight obstacles, and other advantages.