Undo/Redo Operations in Bitmap-Based Collaborative Graphic Editing Systems

Real-time collaborative graphic editors allow a group of users to view and edit the same graphic document at the same time from geographically dispersed sites connected by communication networks. Bitmap-based graphic editing systems are special collaborative editing systems, and Undo/Redo operations are intricate problems in this field. Existing solutions add extra space, thus showing low efficiency of the algorithms. In this paper, based on Multi-version strategy, we propose a new solution to solve the Undo/Redo consistency problem, and consider three possible cases: all-causal, all-independent and causal-independent-mixed operations. In addition, compared with previous collaborative algorithms, the algorithm proposed in this paper supports selective Undo, without requiring additional space and the implementation of Undo/Redo is more flexible.