Eventhandling

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Event handling

The Sc21 event handling system works in the following way:

Events received by the SCView are passed on to the SCController. SCController in turn passes them on to its SCEventHandler, who finally handles them.

The event handler has an outlet nextEventHandler, which can be set to another SCEventHandler, thus forming a chain of event handlers: If an event is not handled by the first event handler, it will be passed on to the next one, and so on - until the event has either been handled or there are no more event handlers in the chain. If an event was not handled by the event handler chain, it is sent back to NSView, and thus passed on to Cocoa's responder chain.

This is one of the few ways where Sc21 behaves differently from Cocoa. In Cocoa, you have to subclass NSView and override a method for each event type you are interested in (mouseUp:, rightMouseDown: etc). There are two reasons why we are doing things differently:

• Sc21 needs a more flexible way to deal with events in order to handle cases where no view is present, i.e. fullscreen mode.
• We wanted to allow the application programmer to add their own event handling capabilities by simply writing her own event handler.

Built-In Event handlers

All Sc21 event handlers must be derived from the SCEventHandler class. Sc21 comes with two built-in event handlers: SCCoinHandler and SCExaminerHandler.

SCEventHandler

SCEventHandler is the superclass for event handlers that takes care of managing the event handler chain. When writing your own event handler, it should be derived from this class. [API doc]

SCEventHandler has two important methods:

- (BOOL)controller:(SCController *)controller handleEvent:(NSEvent *)event;
- (void)update:(SCController *)controller;
controller:handleEvent: is the actual event handling method.

update: is a post-render callback that allows you to do continuous animation (such as needed when simulating a fly mode).

SCCoinHandler

SCCoinHandler takes incoming NSEvents, converts them to SoEvents, and sends them to the Coin scenegraph. [API doc]

SCExaminerHandler

SCExaminerHandler allows you to inspect the scene by rotating, panning, and zooming in and out. An IB inspector makes it possible to set the mouse/modifier key combinations to use. [API doc]

Tutorial

There is a tutorial outlining the basics of how to use the Sc21 event handling system: the Sc21 Tutorial, Part 2 Event Handling.

The CustomEventHandling example distributed as part of the Sc21 distributions demonstrates a slightly more advanced use case, including how to create your own custom event handler.