1. A method for rendering dynamic three-dimensional appearing imagery on a two-dimensional user interface screen of a portable computing device in dependence on a user's view-point of the screen, said method comprising: processing, on a portable computing device, data defining a plurality of user view-points of a user interface screen of the portable computing device; rendering a first image of a constructed scene on the user interface screen based on a first determined user's view-point of the user interface screen of the portable computing device; and rendering a different image of the constructed scene on the user interface screen based on a subsequently determined user's view-point of the user interface screen and thereby presenting the illusion of a three-dimensional image of the constructed scene on the user interface screen.