Package edu.umd.cs.piccolo.event

Class PDragSequenceEventHandler

java.lang.Object
edu.umd.cs.piccolo.event.PBasicInputEventHandler
edu.umd.cs.piccolo.event.PDragSequenceEventHandler
All Implemented Interfaces:
PInputEventListener, EventListener
Direct Known Subclasses:
PDragEventHandler, PPanEventHandler, PZoomEventHandler
public abstract class PDragSequenceEventHandler extends PBasicInputEventHandler
PDragSequenceEventHandler is designed to support mouse pressed, dragged, and released interaction sequences. Support is also provided for running a continuous activity during the drag sequence.

PDragSequenceEventHandler should be subclassed by a concrete event handler that implements a particular interaction. See PPanEventHandler, PZoomEventHandler, and PDragEventHandler for examples.

Version:
1.0
Author:
Jesse Grosjean

  • Constructor Details

    • PDragSequenceEventHandler

      public PDragSequenceEventHandler()
      Constructs a drag sequence event handler instance.

  • Method Details

    • isDragging

      public boolean isDragging()
      Returns true if this event handler is in the process of handling a drag.
      Returns:
      true if handling a drag

    • setIsDragging

      public void setIsDragging(boolean isDragging)
      Used to inform this handler that it is in the process of handling a drag.
      Parameters:
      isDragging - true if handler is processing a drag

    • getMinDragStartDistance

      public double getMinDragStartDistance()
      Returns the minimum distance (in screen coordinates) before a pressed mouse movement is registered as a drag event. The smaller this value the more clicks will be incorrectly recognized as drag events.
      Returns:
      minimum distance a pressed mouse must move before it is registered as a drag

    • setMinDragStartDistance

      public void setMinDragStartDistance(double minDistance)
      Set the minimum distance that the mouse should be dragged (in screen coordinates) before a new drag sequence is initiate.
      Parameters:
      minDistance - in screen coordinates

    • getMousePressedCanvasPoint

      public Point2D getMousePressedCanvasPoint()
      Return the point in canvas coordinates where the mouse was last pressed.
      Returns:
      point in canvas coordinates of last mouse press

    • startDrag

      protected void startDrag(PInputEvent event)
      Subclasses should override this method to get notified of the start of a new drag sequence. Note that that overriding methods must still call super.startDrag() for correct behavior.
      Parameters:
      event - event that started the drag sequence

    • drag

      protected void drag(PInputEvent event)
      Subclasses should override this method to get notified of the drag events in a drag sequence. Note that that overriding methods must still call super.startDrag() for correct behavior.
      Parameters:
      event - event that caused the drag

    • endDrag

      protected void endDrag(PInputEvent event)
      Subclasses should override this method to get notified of the end event in a drag sequence. Note that that overriding methods must still call super.startDrag() for correct behavior.
      Parameters:
      event - event that ended the drag sequence

    • shouldStartDragInteraction

      protected boolean shouldStartDragInteraction(PInputEvent event)
      Returns true if the provided event represents a valid start for a drag sequence. Subclasses should override this method to add criteria for the start of a drag sequence. Subclasses are still responsible for calling super.shouldStartDragInteraction()
      Parameters:
      event - event being tested
      Returns:
      true if provided event is a good start to a drag sequence

    • getDragActivity

      protected PActivity getDragActivity()
      Returns the scheduled activity that's updating the scene as a result to the current drag activity (if any).
      Returns:
      scheduled activity that's updating the scene as a result to the drag activity

    • startDragActivity

      protected void startDragActivity(PInputEvent event)
      Schedules the "infinite" drag activity so that auto-panning and zooming will continue to update the scene even if there are no further drag events fired. For example, if the mouse is dragged to the right while pressing the right mouse button and then paused for a while, the scene should continue to zoom in.
      Parameters:
      event - the event that's responsible for the start of the activity

    • stopDragActivity

      protected void stopDragActivity(PInputEvent event)
      Stops the activity responsible for updating the scene.
      Parameters:
      event - The event responsible for stopping the drag activity

    • dragActivityFirstStep

      protected void dragActivityFirstStep(PInputEvent event)
      Subclasses override this method to get notified when the drag activity starts stepping.
      Parameters:
      event - the event responsible for the first step in the drag activity

    • dragActivityStep

      protected void dragActivityStep(PInputEvent event)
      During a drag sequence an activity is scheduled that runs continuously while the drag sequence is active. This can be used to support some additional behavior that is not driven directly by mouse events. For example PZoomEventHandler uses it for zooming and PPanEventHandler uses it for auto panning.
      Parameters:
      event - the event encapsulating the callback context for the activity step

    • dragActivityFinalStep

      protected void dragActivityFinalStep(PInputEvent aEvent)
      Subclasses should override this method to get notified when the drag activity stops stepping.
      Parameters:
      aEvent - the event responsible for ending the activity

    • mousePressed

      public void mousePressed(PInputEvent event)
      Subclasses should not override this method, instead they should override the appropriate drag callbacks.
      Overrides:
      mousePressed in class PBasicInputEventHandler
      Parameters:
      event - The event to be queried about the details of the mouse press

    • mouseDragged

      public void mouseDragged(PInputEvent event)
      Subclasses should not override this method, instead they should override the appropriate drag method.
      Overrides:
      mouseDragged in class PBasicInputEventHandler
      Parameters:
      event - The event to be queried about the details of the mouse press

    • mouseReleased

      public void mouseReleased(PInputEvent event)
      Subclasses should not override this method, instead they should override the appropriate drag method.
      Overrides:
      mouseReleased in class PBasicInputEventHandler
      Parameters:
      event - The event to be queried about the details of the mouse release