| |
|
InteractorsInteractors abstract event-handling on the canvas into higher-level objects. Each figure can have a single interactor attached to it, and that interactor handles all events that occur on that figure. Interactors can be shared by many figures, allowing one interactor to be set up to produce a consistent behaviour by all figures attached to it. (For example, in a graph editor, all nodes would have the "node interactor" attached to them, while all edges would have the "edge interactor" attached to them.)
The top-level Interactor interface extends both LayerListener and LayerMotionListener, so in general interactors can respond to any type of layer event. In addition, it has methods to enable and disable the interactor, and to query it for whether is can handle motion events. When a mouse-pressed or mouse-entered event occurs on a figure, the event dispatching code finds the clicked-on figure and tries to forward the event to its interactor, if it has one. Before doing so, however, it calls the accept() method to see if the interactor is prepared to deal with that event and the subsequent events (drag and release events, or motion and leave events) on that figure. Each interactor has an associated MouseFilter that should be used to check whether an event should be accepted. The AbstractIteractor class implements most of the Interactor methods. Shown here are two concrete subclasses: CompositeInteractor, which can have other interactors attached to them, and DragInteractor, which drags a figure or figures about on the screen. CompositeInteractor adds the notion of listening interactors, with the methods addInteractor() and removeInteractor(). CompositeInteractor forwards events to attached interactors -- this allows, for example, multiple kinds of interaction to be attached to a single figure (dragging if one mouse button is pressed, drawing if another is pressed, for example). A subclass of CompositeInteractor, SelectionInteractor, is generally attached to figures that can be added to a selection. It adds the notion of a selection model and a selection renderer (which is used to highlight the items in a selection). When an item is clicked-on, it adds or removes that item from a selection model, and then forwards events to attached interactors (which could, for example, move the objects in the selection). The DragInteractor class deal specifically with the press-drag-drag-drag-release sequence of events encountered in direct manipulation and dragging. At adds the notion of PointConstraint, which is used to constraint the mouse cursor position, for doing such things as gridding, keeping a figure within a region of the screen, and snapping to target objects. A series of PointConstraints can be added to DragInteractor, and they are processed in order. DragInteractor also accepts an additional LayerListener. This listener is notified when the interactor receives a mouse event, and is intended to allow clients to perform initialization of the interactor prior to the default processing performed in response to that event. For example, an interactor could set up PointConstraints depending on the current context in the mousePressed() method of this listener.
|
