Part IV. The Editor Widget

# The Editor Widget

For every xml node in the document, there is a CongEditorNode for each editor_widget3. There is a class hierarchy of `CongEditorNode` subclasses, so, for instance, there's a CongEditorNodeElementStructural which is used for structural tags, and a CongEditorNodeComment for comments. This way, we only have to figure out what type a node is once, rather than every time we visit it, plus we can store useful state in the `CongEditorNode` objects. For example, in a CongEditorNodeText, we store a `PangoLayout`.

There is also a collection of CongEditorArea objects. These form a hierarchical tree of rectangular areas which divide up the space allocated to the widget. They know how to draw themselves, can be clicked on, handle size negotiation etc. They are a little bit like a lightweight version of `GtkWidgets`, although the analogy isn't perfect.

`CongEditorArea` objects are what you see and click on when interacting with the editor_widget3, although not all of them are visible (e.g. CongEditorAreaComposer which exists purely to manage the sizing of its children).

`CongEditorNode` objects work behind the scenes. They are responsible for creating `CongEditorArea` objects to represent themselves.

There are a few other classes involved: CongEditorAreaFlowHolder, and CongEditorChildPolicy. These are responsible for generating paragraph-like areas, which the editor nodes "pour" their `CongEditorAreas` into. This allows us to get the nice underlines, which is achieved by using a `PangoLayout` for every text node, splitting all the `PangoLayoutLines` into separate `CongEditorArea` objects, and then merging them, together with a few extra `CongEditorAreas`.

### Tip

If you want to see the `CongEditorAreas`, then go to `src/cong-editor-area.c` and play around with the #define settings; in particular `DEBUG_RENDER_ALLOCATIONS` can be used to render rectangles to indicate all of the bounding boxes of the CongEditorAreas.

### Tip

When working on layout code, it may help to turn up the font sizes so that everything is much larger on your screen. You can do this by editing `src/cong-app.c` and defining `TEST_BIG_FONTS` to be `1`.