Introduction

This section describes a whiteboard tool built on top of TGIF: TGWB (Tangram Whiteboard). TGIF (Tangram2 Graphic Interface Facility) is a Xlib based interactive 2-D drawing facility under X11. The tgif tool is a powerful vector based drawing tool. The user draws objects, i.e., rectangles, lines, circles and splines, over a drawing area. Objects may be transformed - for instance, rotated, translated and flipped. New objects may be constructed by grouping other objects. The tgwb allows simultaneous modifications in drawings by users in a group. It is a versatile multicast distributed tool. TGWB interface is shown in Figure , where two users are editing a Tangram-II model.

Figure: TGWB: Tangram Whiteboard interface.

Distributed whiteboards must ensure that every member in a session has the same view of the drawings. A Reliable Multicast Library and a total ordering mechanism was developed to allow reliable multicast transmission and member view consistency. Further information about those issues can be found at [#!rmcast_site!#].