The four point arrays representing the circuit are shown in Table 3.9 . By storing these coordinates, the implementation relieves itself from having to recalculate the center of the point based upon the canvas coordinates of the polygon. In Tcl, this can be accomplished with a call to the llength list procedure.
G has degree three.
This array is consulted when the user moves a point which is connected to a component port. In this situation, the array maps the point identifier to the corresponding port identifier to which it is connected. From this, the implementation can determine the unique tag name of the component which is to be moved in unison with the point. The array is also used to map identifiers in the reverse direction when the user moves a component attached to one or more wire points. Given the identifier of the point, the text label canvas item associated with that point can be obtained, thereby allowing the label to be subsequently modified or deleted by the implementation.