EMF Compare/GMF Notation model Comparison

The GMF diagram comparison task can be splitted into four parts. First, we must be able to compare GMF Notation models, then we have to know how we handle the link with the comparison of the semantic model (i.e. the elements represented by the diagram). Third, we have to know how to integrate existing GMF editor within the EMF Compare editor. Finally, we have to know how to create generic markers on the diagram to give a feedback of the computed differences to the user.

Notation model comparison

Notation model comparison need its own MatchEngine and DiffEngine. The whole notation metamodel will not be taken into account. The difference computation will only occur on a subpart as depicted below:

The nodes and edges will be matched by their XMI IDs. Containment between nodes will be handled in a generic way (i.e. by the super class GenericMatchEngine).

Only following differences will be computed:

Addition / Removal of a node
Addition / Removal of an edge
Change of a Label on an edge or on a node
Move of a node within the diagram (with a configurable translation threshold for the move its location x/y).
Move of an edge within the diagram (total number of bendpoints, change of bendpoints - sourceX, sourceY, targetX, targetY - and positions of the anchors).

Link with the semantic comparison

For many cases, we need the semantic comparison to be done before the graphical one. The work on logical model integration should give us this facility by computing the differences of a whole resource set instead of just the current resource containing the notation model.

The link with the semantic comparison had to be provided for the labels. For each element , we have to get the text of the label and compare them. They are not stored directly into the notation model.

Move operations of Edge and Node never correspond to semantic change.

For addition and removal of nodes and edges, graphical differences may or may not corresponds to a semantic change. For instance, a graphical element may be removed because it has been hidden or deleted from the diagram. It does not correspond to a change in the semantic model. This graphical change does not have to be linked to a semantic change. In the other case, the addition or the removal of a node or an edge must match an addition or a deletion in the semantic model.

Merge

As a we don't know from the notation model how labels are build and from which feature(s) of the semantic model, the merge operation of labels modification must be applied on the notation model to trigger the appropriate underlying commands on the semantic model. This merger operation can be triggered only if the label is editable (=> ask to the editpart of the view isEditModeEnabled())

The merge of a move a node or an edge never triggers a merge on the semantic model, only on the graphical notation. The merge is a simple copy of values of bendpoints/layout constraints.

Addition/Removal of node or edge trigger the merge of the semantic difference if it is associated to one, and the merge operation of the graphical difference otherwise. This merge operation consist of re-create the element if it has been deleted from the diagram, or to restor the hidden status of this view (View.isVisible())

GMF editor integration within Comparison editor

The integration of GMF editor within the comparison editor has to be done through specific contentMergeViewer (org.eclipse.compare.contentMergeViewers extension point) and maybe a specific structureMergerViewer (org.eclipse.compare.structureMergeViewers extension point) to provide the separation between graphical differences and semantic differences.

The content merge viewer has to instantiate DiagramGraphicalViewer inside its createControls() method:

viewer = new DiagramGraphicalViewer();
viewer.createControl(composite);
viewer.getControl().setBackground(ColorConstants.listBackground);

The resize of the left/right/ancestor panes has to be handled gracefully like this:

viewer_left.getControl().setBounds(x, y, leftWidth, height);
viewer_right.getControl().setBounds(x + leftWidth + centerWidth, y, rightWidth, height);

Initialization

The left/right/ancestor viewers has to be initialized with a proper editing domain. This creation takes the resourceSet as input:

DiagramEditingDomainFactory.getInstance().createEditingDomain(resourceset);

Then, the viewers has to be configured like this:

viewer.setEditDomain(new DefaultEditDomain(null)); // GEF editDomain
viewer.setEditPartFactory(EditPartService.getInstance());
viewer.setRootEditPart(new DiagramRootEditPart(diag.getMeasurementUnit()));
viewer.setContents(diag); // the diagram from the notation model

It is also possible to make the viewer uneditable by browsing all children of the rootEditPart of each viewer, but then, we will not be able to ask for the editability of views. It should be better to add a top layer that forbid the editing.

Markers for GMF diagrams

Difference marker on notation model are provided by using the org.eclipse.gmf.runtime.diagram.ui.decoratorProviders extension point.

The provided IDecoratorProvider will create a decorator based on the proposed IDecoratorTarget. This IDecoratorTarget can be adapted to a Notation View like this :

View view = (View) decoratorTarget.getAdapter(View.class);

The decorator should be created if, and only if, there is a graphical difference associated with the given View. The graphical difference model will be retrieved from the owning EditPart.

Provided decorators has to implement IDecorator interface.

The issue with specific decorator is to define the locator. Each Figure has its own bounds and we will start from the assumption that:

Marker of decorated figure will be rectangle following their bounds (smallest rectangle completely enclosing the IFigure)
Marker of decorated edges will be handled for polylines only and bounds of the decoration will be the bounds of the decorated
Marker of move will be an icon (picture not yet defined) located:
- in the middle of the edge if the edge has moved
- in the top right of the bounds of the figure if it is a node.

See samples of first annotation prototypes (on Ecore diagram):

Class added: