1. A virtual environment system comprising: apparatus for producing a virtual environment on a projection plane; a planar mirror, the planar mirror being of substantial size relative to the projection plane and being positioned relative to the projection plane such that the plane of the mirror intersects the projection plane and the angle of the mirror relative to the projection plane is such that a user of the system who looks at the mirror sees the projection plane reflected therein; and a tracker that tracks the position and orientation of the eyes of a user of the virtual environment system, the apparatus for producing the virtual environment receiving a current position of the mirror and producing a first virtual environment on the projection plane when the tracker indicates that the user is looking at the mirror and a second virtual environment on the projection plane when the tracker indicates that the user is looking at the projection plane.