The detailed semantics of graphics input devices

The concept of virtual input devices, enunciated by Wallace, has been the accepted basis for producing device-independent interactive graphics systems. It was used by GSPC for the Core System, and it underlies the draft international standard GKS. During the recently concluded technical review of GKS, the input facilities became a bone of contention. The discussions revealed many inadequacies in the virtual input device concept, and were finally resolved using a refined and extended model of input, which is presented here by some of the participants in the discussions. Examples are included, showing how the GKS facilities derive from the model, and the Core's “STROKE” device is used to show how the model controls future extensions to GKS. The model is also used to describe the other differences between the input facilities of the Core System and GKS.