A computer graphic method is described for simulation of calligraphic pens and brushes. Unlike a paint system which uses a mouse, here the artist uses a force-transducing pen to create realistic pen or brush strokes in real time. The system has been used for the production of western-style calligraphy and for writing with brush-based alphabets such as kanji. Successive values of x, y, and pen-tablet force are measured, and others are derived–such as velocity, accumulated stroke length, and stationary dwell time. These are all used to define the momentary geometric footprint of pen or brush; the incremental geometry of the stroke depends in turn on rules for connecting successive such footprints. Additional rules may apply at the beginning or end of the stroke. Crucial to the real-time aspects of the method are a very fast means for computing the momentary footprint, and for defining and filling the area connecting the current footprint with the previous one. This high-speed processing permits regular, uninterrupted acquisition of input data (thus avoiding improper polygonal faceting of curved strokes) and it produces a screen display without noticeable delay. Later, hard copy output may be produced at higher resolution by recomputing from the same data.
- Ken Knowlton & Karen Donoghue, Freestyle/Advanced Technologies Group, Wang Laboratories, Inc., USA