The View function allows you to concentrate on different aspects of diagrams by hiding or showing selected object or relationship types. The menu selection View | Selected... opens a selection dialog, as in Figure 4-19, allowing you to choose the object and relationship types to be shown.

To select object or relationship types to be viewed mark them with a tick ‘ü’. For example, according to the selection dialog below all components of the WatchApplication diagram are shown.

Relationships involving hidden objects are only shown if they also involve at least one object that is not hidden. Figure 4-20 shows the result of hiding State objects in a Watch Application Diagram. Note that this example is intended to highlight how the hide functionality works: more sensible choices of objects to hide here would be the black Action and Variable objects.

Similarly, View | All shows every object and relationship of a diagram. Hence, this command automatically selects every object and relationship type in the selection dialog (Figure 4-19).

The use of large diagrams necessitates that they can be displayed at different scales. In Diagram Editor there are several ways to set and alter the scale factor. To set the zoom to a fixed percentage:

Alternatively, you can select a predefined zoom factor, fit or default zoom from the zoom pull-down list located at the lower-right corner of the Diagram Editor window. You can also enter a new zoom value if needed. Pressing the + and – buttons on the either side of the pull-down list will increase or decrease the zoom factor by one unit. Default and fit zoom can be also set by pressing the respective toolbar buttons.

It is also possible to zoom freely on the defined area. In order to do this:

You can also zoom in and out directly in the drawing area by holding down Alt and using the mouse scroll wheel. The current zoom level is shown in the status bar at the bottom of the Diagram Editor.

To help make your diagrams look neater, MetaEdit+ can show a grid over the diagram, to help you align objects with it. The size of the grid is controlled through the View | Choose Grid... dialog. The command View | Show Grid or toggling the Show checkbox on the status bar at the bottom of the window allows you to show or hide the grid in the diagram. Merely showing the grid does not affect object placement, however; the command View | Align to Grid aligns the selected object and relationship centers and role break points according to the selected grid. If there is no selection, all elements are affected. Align to Grid is also available as a button in the toolbar.

You can force the use of the grid when elements are created or moved by selecting View | Snap to Grid or checking the Snap checkbox at the bottom of the window. The centre of individual elements and role break points will be aligned to the grid in all operations. If multiple elements are selected and moved, they will maintain their relative positions to each other, and the whole area will maintain its relative offset to the grid. Thus elements that were previously aligned with the grid will still be aligned after the move.

As with zooming you can also access the grid setting through a pop-up menu by pressing the right mouse button when nothing is selected in the diagram.

With its tidy drawing operations, forced refreshing of the Diagram Editor window is not needed very often. However, refreshing the display is needed when changes made to the conceptual graph by some other editor need to be propagated to the currently open diagram. Similarly, changes made to the underlying metamodel also require forced refreshing. The display can be refreshed by choosing View | Refresh or pressing F5.

You can scale an object or relationship symbol by selecting it and dragging any of the selection handles at its corners or the midpoints of its sides. Holding Shift down will maintain the aspect ratio of the symbol. Holding control down will scale the symbol keeping the point opposite the dragged selection handle in the same place. Without control the centre of the object is maintained in the same place, as this best maintains the layout of the diagram – keeping the object on its grid point and keeping role lines at the same angle.

To set a particular scale, or scale several elements with the same scale factor, choose Scale symbol... from the element’s pop-up menu or from Format menu. The Scale Dialog that opens will initially show the current scale of the (first) selected object. Pressing Default will remove any scaling, returning the elements to their default size.

The diagram elements appear on Diagram Editor in the following order: roles are displayed over relationships, which are displayed over objects. Whilst ordering amongst roles and relationships is automatic, the order of the objects is user definable. To re-order objects:

Note that Bring to Front will only make this the uppermost object: it will still be below all relationships and roles.