8.1 System Events ¶

Modern integrated System On a Chip (SOC) hardware has many circuits which are active at the same time. So one kind of event is sensing something happening in the world. Class EventSensor handles keyboard key press and mouse hardware interrupts, translating between hardware signals and software event objects.

Basically, a morph raises its hand and says what events, if any, it is interested in receiving. Then it implements methods to get the event objects holding the information of the captured events. In Cuis-Smalltalk, the class MorphicEvent and its subclasses represent the diversity of events in the system.

MorphicEvent
   DropEvent
   DropFilesEvent
   UserInputEvent
      KeyboardEvent
      MouseEvent
         MouseButtonEvent
         MouseMoveEvent
         MouseScrollEvent
      WindowEvent

As MouseMoveEvents are generated, the HandMorph adjusts its screen position. When mouse and keystroke events arrive, the HandMorph coordinates the “dispatch” of events to the proper morph under the hand as well as displaying tool tips and carrying morphs in transit during drag operations.

As we saw in the previous chapter with ColorClickEllipse, any morph may override default Morph methods to assert that it handles various user events and the methods which take the associated event objects when events arrive.

Basically, user input events are generated, a HandMorph reflects any cursor movement, morphs react to events, each long running task gets a time slice and makes some progress, any display changes are updated on the screen, and the next step happens. Time marches forward a step.

This happens over and over and over, keeping the juggler’s illusion that all balls in the air are moving at once. Underneath, the balls are each moving just a bit, in sequence.