Colour Picking
For every ARToolkit pattern (picture 1) a plane of size x*y is registered but not rendered in the application (picture2). This arPattern object allows determining the exact position of a 2D mouse cursor independent of the plane's position and orientation. This is realized by colouring the plane's vertices with red and green and interpolating between colours (picture 3). If a plane object is picked with the mouse, it is selected and the pixel colour under the cursor is retrieved. The colour code is used to specify exact position of the cursor on the plane. This position is used together with key / mouse events to realize interactive interface elements. Picture 4 illustrates this idea using a custom video player.