Appearance-preserving manipulation of hand-drawn graphs

Abstract

We describe a sketching system that allows users to create and manipulate directed graphs, such as those depicting state diagrams, using pen-input alone. The system exactly preserves the user's strokes, which may be entered in any order, and depicts them with a chalk texture to evoke a blackboard metaphor. The system automatically interprets the geometry of the sketch, distinguishing vertices, edges, and arrow heads, then tacitly imparts the intended graph semantics based on the two-dimensional placement of these elements. Once drawn, the user can manipulate the directed graph gesturally using the pen. The system responds to vertices or edges being picked and dragged by adjusting all adjacent edges appropriately. The original appearance of the hand-drawn vertices and edges is maintained even while their shapes are continually morphed in response to rearrangement of these elements. All edges exhibit shape memory, which is the proclivity to return to their original hand-drawn shape despite repeated stretching and compression.