Cross-platform Qt-based implementation of low level GUI layer of ROOT

This paper describes an implementation of the low-level layer of the ROOT package based on the multi-platform graphics library. This approach allows ROOT developers and ROOT users to work with a code that has no X11/WIN32 graphics subsystem dependencies and at the same time opens an unrestricted access to a rich set of ready-to-use commercial and free GUI Qt-based widgets, which are available for download from http://root.bnl.gov Web site.