Graphical Editing Framework in Java

Drawer QR in Java Graphical Editing Framework
CHAPTER 9 Graphical Editing Framework
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Figure 9-1
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GEF dependencies
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91 Draw2d
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Figures lie at the heart of the Draw2d toolkit Figures can consist of children figures, which are painted inside the parent s bounds and arranged by a layout manager A LightweightSystem coordinates the Canvas with the set of figures by forwarding nonpaint events from SWT using an EventDispatcher Paint events are forwarded to the UpdateManager, which coordinates painting and layout, as shown in Figure 9-2
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911 Figures
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Because Figures figure so prominently in Draw2d, let s discuss their general responsibilities as defined in their extensive API Following are some highlights; the rest of this section goes into more detail on their use Figures are responsible for the following:
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Adding and removing child figures Adding and removing listeners (for example, coordinate, figure, focus, key, layout, ancestor, mouse, and property change listeners) Calculating whether a point falls within the figure bounds (hit testing) Locating a figure for a given location Returning the figure s border, bounds, location, ToolTip, color, font, transparency, visibility, and so on
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91 Draw2d
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Accessing the figure s update and layout manager Painting and validating Setting and getting focus Handling events for structural changes, movement, resizing, and so on
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Figure Canvas SWT Canvas LWS
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Update Manager
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Root Figure
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Event Dispatcher
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Contents Content Root
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Figure
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Figure
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Figure
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Figure 9-2 Draw2d lightweight system
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Figure 9-3 illustrates a user interaction scenario to describe how these elements work together
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912 Text
In addition to figures, Draw2d has support for text Labels (orgeclipse draw2dLabel) are the primary means, while rich text features are also available in the orgeclipsedraw2dtext package This allows for wrapping content such as a paragraph, mixing nontext with text (Tufte would love this!), supporting bidirectional support, and more
CHAPTER 9 Graphical Editing Framework
1 User Interaction Figure Canvas 6 Validates Invalid Figures, Paints Dirty Region
2 Listener Notifies LWS
3 Delegates to SWT Event Dispatcher
Update Manager
Root Figure 5b Revalidates and Marks Root as Invalid 4 Dispatches Figure Events
5a Requests Repaint of Dirty Region
Content Root
Figure
Figure
Figure
Figure 9-3 Draw2D interaction sequence
913 Painting
The following sequence illustrates the process of figure painting
paint() This method is declared on the interface and kicks off the
painting process First, properties are set on the graphics that children would inherit, including font and background and foreground color Then the graphics state is pushed so that just these inherited settings can be restored when painting children Next, the following methods are called:
paintFigure() The figure paints itself, although figures are not
required to paint at all A simple form of painting is to fill in the bounding box with the figure s background color
paintClientArea() The client area is where children appear This method should apply any changes to the graphics that affect only children, such as coordinate system modifications and translating the graphics
91 Draw2d
to the client area This method also clips the graphics to the region where children are allowed to appear
paintChildren() Now that the client area is set up, children are
painted After each child paints, the graphics state is restored to the incoming state so that children do not overwrite the inherited graphics settings from the parent
paintBorder() Finally, the figure paints decorations that should appear on top of the children If a border has been set on the figure, it paints now
Figures are composed in trees, structurally speaking, so they are painted by traversing the tree in depth-first order As an example, consider the tree in Figure 9-4 and the Z-order depicted in the corresponding image to the right
1 23 6
Figure 9-4
Figure composition
Children within figures cannot paint outside their parent s bounds Clipping occurs while figures are painted and is cumulative for the entire parent hierarchy Figure 9-5 is a simple figure hierarchy and shows the result of clipping on its rendition
Figure 9-5
Figure clipping
CHAPTER 9 Graphical Editing Framework
914 Layout
Draw2d provides layout using two steps: first by marking figures as invalid if they need layout, and second by validating branches of invalid figures Layout occurs all at once because Draw2d employs a deferred update strategy and, therefore, avoids displaying intermediate states when multiple figures become invalid Draw2d uses the term validation to perform layout The validate() method can be extended to perform other functions that require integration with the update manager When the validate() method is called, a figure performs its layout and then validates its children Layout requires information on the size of children figures, so methods are provided for querying minimum, maximum, and preferred sizes If you know an available dimension, you can pass it as a hint to a figure when querying, which instructs the figure to consider the dimension when it returns its size requirements If a figure changes so that layout is required, it calls revalidate() to mark itself as invalid and requesting revalidation on its parent This continues up the hierarchy and ends with an entry in the update manager s list of invalid figures The update manager performs top-down layout by first setting the bounds of the parent and calling validate() on its children