The first part consists of determining which viewers in the tree should handle an event. This is called picking . The second part consists of sending the viewer the event so that it can dispatch it to the correct method. Scenario 2 is a scenario for Object Diagram 1 used to describe geometry management. Take a quick tour of the diagram and then read on about picking and dispatching.
Picking begins by a call to pick on the root glyph.
The root then determines if the event occurred within its allocation. This occurrence is called a hit . If the root is a geometry managing object the pick call forwards the call to its body its children for picking. If some glyph within the viewer calls hit on the picker, pick preserves the chain, otherwise pick removes the picker before returning. When pick returns in root, the picker object will be the first link in a chain of pickers leading to the viewer that will dispatch the event.