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When a rule is executed, the figures in the rule's head are replaced with
figures from the rule's body. The previous section of this tutorial explained
how the figures in the rule's head are matched to figures connected to a mouse
event. This section explains how figures in the rule's body are interpreted by
the Vispatch system. Before the Vispatch system can place copies of figures from the body in the Vispatch document, it must first compute the location for each figure. Rules can contain three special figure types that specify how the Vispatch system should compute the locations. The simplest of these is the equiv line figure which tells the Vispatch system to reuse the location of an already used point. The other two are point generator figures, which tell the Vispatch system to compute a new location based on a geometric relationship. This section also explains the meaning of event figures when they appear in rule bodies. |