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Eclipse GMF Guide
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Tutorial: Creating Connections

Version: 0.1

Date: August 11, 2005

Contents

- Overview

- References

- Introduction

- Create a new connection type

- Drawing connections between shapes

- Connecting wires at fixed anchors

- Summary

Overview

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This tutorial provides the reader with the steps to create a new connection within a diagram client.

References

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This tutorial references the following tutoral:

Create a shape

Introduction

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In this tutorial, we will use the Logic Diagram Example to illustrate how to add a connection edge to a diagram. We will use the wire connection as the example. To gain familiarity with the Logic Diagram Example, refer to the Logic ExampleGuide.

Create a new connection type
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Most diagrams have a need to display semantic relationships that exist between elements.  In the Logic example, this is also the case.  There is an element called ?Wire? which allows logic elements to be connected to each other.  It is literally the wire that carries electricity between terminals on circuits and LED elements in the circuit board.  The mechanism for adding a connection shape on a diagram is very similar to how a shape is added except for some subtle difference in API.  This is summarized below.

Example: LED connected by wires

Adding a Wire palette entry to the contribution for the palette provider

See section #Add entries tothe contribution for the palette provider.

Adding a new Wire creation tool instrumented from a palette factory class

A new condition needs to be added in the LogicPaletteFactory class in the createTool method.  For a connection a ConnectionCreationTool instance is created passing in an IElementType hint (wire) that will be sent in a request to return a command for creating the connection.

Add new View provider entry

In order to respond to the tool request we need to create a provider for creating the notation (View) for the new shape.  First it is necessary to add plug-in.xml extension for the org.eclipse.gmf.runtime.diagram.core.viewProviders extension point.  We indicate the viewClass context (org.eclipse.gmf.runtime.notation.Edge) and provide a hint for our provider to be invoked upon (wire).  Similar to #Add new Vie w provider entry a mapping of the hint to the view class that will construct the connection notation is necessary in the getConnectionViewClass method.  The WireView.java class will serve this purpose.  The WireView class subclasses from AbstractConnectionView.  Please refer to the WireView class for details of what initialization is needed.

Add new Editpart provider entry

Refer to #Add new Editpartprovider entry on how to add a plugin.xml entry for a org.eclipse.gmf.runtime.diagram.ui.editpartProviders extension. In the LogicEditPartProvider class there is simply a mapping from the View class to the EditPart class that needs to be created in the getConnectionEditPartClass method.  The WireEditPart class contains code for managing creating the IFigure (PolylineConnectionEx ) class and responding to property change events.

Drawing connections between shapes

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The notation meta-model stores all layout constraint units (positions, bendpoints and anchors) in HiMetric units (0.1 millimeter).  This allows for a high level of precision when dealing with zoomed in diagrams.  This adds some complexity to the figure display since GEF assumes pixel units when drawing figures onto the canvas. 

In the case where we wish to connect 2 LED shapes via a wire connection, we'll need to do some conversion of the pixel values to HiMetric before the connection can accurately connect to the LEDFigure.  The function MapMode.DPtoLP(int deviceUnit) is used to convert a Device Unit (pixels) into a Logical Unit.  This method needs to be instrumented in the LEDFigure when drawing the connection nubs around the shape.  Additionally by abstracting the pixels through this MapMode, it will allow the platform to support a different coordinate systems in the future without affecting clients. 

A somewhat unique aspect of the Logic example is that the wires don't connect directly to the top level shapes.  They always connect via terminal elements that exist on the borders of the shapes.  If we consider the LED shape, it has 8 terminals surrounding it where 4 are incoming terminals and 4 are outgoing terminals.  To accomplish this, it is necessary to have a separate view represent the terminal on the border of the LED view.  The terminal views on the LED are essential to the functionality of the LED so they need to be represented all the time.  This is referred to as a canonical representation.  The means that the children of a particular view are always fully synchronized with the corresponding semantic element children. 

There is a facility in the diagram layer that can manage this synchronization called the CanonicalEditPolicy.  This EditPolicy is installed on an EditPart and is responsible for managing the creation of child views that need to be created if a semantic child exists.  The LEDEditPart has a subclass of this EditPolicy called LogicCanonicalEditPolicy that discovers the terminal children of the LED semantic element and creates corresponding terminal views for each terminal element.

Connecting the wires at fixed anchors

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The default behavior when connecting to a shape allows the end of the connection to be anywhere around the source or target shape.  In the case of the wire connection, we want it to connect at a very specific location on the terminal and don't need to have the flexibility of moving it around the shape.  The anchoring behavior is handled in the IFigure hierarchy through the ConnectionAnchor interface.

To change the default behavior, we need to override some methods in the IFigure implementation to return a different anchor.  In the LEDFigure class the getSourceConnectionAnchorAt and getTargetConnectionAnchorAt functions need to be overridden in LEDFigure and return a anchor that will return a fixed point with the figure bounds.

In LEDFigure:

       /*

        * @see org.eclipse.gmf.runtime.gef.ui.figures.NodeFigure#getSourceConnectionAnchorAt(org.eclipse.draw2d.geometry.Point)

        */

       public ConnectionAnchor getSourceConnectionAnchorAt(Point p) {

              if (p == null) {

                     return getConnectionAnchor(szAnchor);

              }

              return fixedAnchor;

       }

public Vector getSourceConnectionAnchors() {

       return outputConnectionAnchors;

}

           

Support for reconnection between two shapes at fixed anchors

When creating or reconnecting a wire between terminals on the logical example, this is not only

changing the notation by moving the end points, it is also changing the underlying semantic model that the diagram is representing.  This behavior is centralized with-in the EditHelper for wire metaModelType.  The WireEditHelper overrides the AbstractEditHelper#getReorientRelationshipCommand to return the command that handles reorient of the logic wire element.  For instance, when a palette tool is invoked, it is sending a request that is handled by the SemanticEditPolicy which in terms handles the creation.  Similarly when the user reorients the end of a wire in the logic example, a request is sent automatically by the infrastructure to the SemanticEditPolicy which determines if there is a metaModelType registered that can handle the request.  In this case the wire metaModelType would be found and would return the WireEditHelper which can provide a command for this request that subsequently gets executed making the changes against the logic semantic model.

In WireEditHelper.java:

       /**

        * Gets a command to change the source or target of a wire.

        */

       protected IEditElementCommand getReorientRelationshipCommand(

                     ReorientRelationshipRequest req) {

              return new ReorientWireCommand(req);

       }

Summary

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In this tutorial, we did the following:

  1. Created a new connection wire for display on the diagram editor..
  2. Learned how to connect 2 shapes using the new connection type..
  3. Created fixed anchors for the connection to attach it's ends to.


Copyright (c) 2000,2005 IBM Corporation and others. All Rights Reserved.




 
 
  Published under the terms of the Eclipse Public License Version 1.0 ("EPL") Design by Interspire